NEET Ultimate Masterclass: Human Physiology (Class 11)

1. Introduction: The Heartland of NEET Biology

Human Physiology is the cornerstone of the NEET (National Eligibility cum Entrance Test) Biology syllabus. Comprising roughly 20–25% of the total Biology weightage, this unit contributes between 12 to 18 questions annually. For a medical aspirant, mastering these seven chapters is not just about clearing an exam; it is the fundamental precursor to your MBBS curriculum.

The beauty of Human Physiology lies in its logic. Unlike the heavy memorization required for Plant Diversity, Physiology follows the principles of homeostatic balance, negative feedback loops, and elegant biochemical pathways. This study resource is designed specifically for the NEET "Direct NCERT-based" trend while incorporating the "Critical Thinking" edge required for Assertion-Reason (A-R) and Statement-based questions introduced recently by the NTA.

In these notes, we bridge the gap between simple reading and active recall. Each chapter is distilled into high-yield points, comparative tables, and "NCERT-Killer" mnemonics. We will dive deep into the mechanics of breathing, the electrical conducting system of the heart, the counter-current mechanism of the kidney, and the synaptic transmission of nerves. Use this resource as a primary learning tool or a comprehensive final revision guide. Let’s decode the human machine.

2. Digestion and Absorption

Digestion is the process of conversion of complex food substances to simple absorbable forms.

2.1 The Alimentary Canal: Structural Blueprint

The human digestive system consists of the Alimentary Canal and Associated Glands.

• The Mouth and Teeth:

  • Thecodont: Teeth embedded in sockets of jaw bone.
  • Diphyodont: Two sets of teeth (Deciduous/Milk and Permanent).
  • Heterodont: Different types of teeth: Incisors (I), Canines (C), Premolars (PM), and Molars (M).
  • Dental Formula (Adult): $\frac{2123}{2123} \times 2 = 32$.

• The Wall of Alimentary Canal (Histology): From outer to inner:

  1. Serosa: Outermost thin mesothelium.
  2. Muscularis: Inner circular and outer longitudinal smooth muscles.
  3. Sub-mucosa: Loose connective tissue containing nerves (Meissner's plexus), blood, and lymph vessels. DUODENAL GLANDS (Brunner's Glands) are found here.
  4. Mucosa: Innermost layer. Forms Rugae in the stomach and Villi in the small intestine.

2.2 Digestive Glands

1. Salivary Glands: Three pairs—Parotids (cheek), Sub-maxillary/Sub-mandibular (lower jaw), and Sub-linguals (below tongue).
2. Liver: Largest gland (1.2 to 1.5 kg). Consists of hepatic lobules (structural and functional units). Glisson’s Capsule is a thin connective tissue sheath covering each lobule.
3. Pancreas: Compound (both exocrine and endocrine) organ. Exocrine part secretes alkaline pancreatic juice containing enzymes.

2.3 Physiology of Digestion

Digestion is a mechanical and chemical process.

Mnemonic for Proteolytic Enzymes: "Try Chewing Chunks" (Trypsin, Chymotrypsin, Carboxypeptidase).

2.4 Absorption and Disorders

• Absorption: Passive (Simple diffusion), Facilitated (Glucose/Amino acids with Na+), and Active.
• Fats: Cannot be absorbed directly. They are incorporated into Micelles, then reformed into Chylomylcrons (protein-coated fat globules) and transported into Lacteals (lymph vessels).
• Disorders:
  • Jaundice: Liver affected; skin/eyes turn yellow due to bile pigments.
  • PEM (Protein Energy Malnutrition): Marasmus (deficiency of proteins and calories, occurs in infants <1 year) vs. Kwashiorkor (deficiency of protein only, occurs in children >1 year).

3. Breathing and Exchange of Gases

Respiration involves the atmospheric $O_2$ being traded for $CO_2$ produced by the cells.

3.1 Mechanism of Breathing

Breathing involves two stages: Inspiration and Expiration.

• Inspiration: Occurs if the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure (negative pressure).
• Muscle involvement: Diaphragm and External Intercostal Muscles (EICM) contract $\rightarrow$ Thoracic volume increases $\rightarrow$ Pulmonary pressure decreases $\rightarrow$ Air rushes in.

3.2 Respiratory Volumes and Capacities (High Yield)

• TV (Tidal Volume): 500 mL.
• IRV (Inspiratory Reserve Volume): 2500–3000 mL.
• ERV (Expiratory Reserve Volume): 1000–1100 mL.
• RV (Residual Volume): 1100–1200 mL. (Cannot be measured by spirometry).
• VC (Vital Capacity): $ERV + TV + IRV$.
• TLC (Total Lung Capacity): $VC + RV$.

3.3 Exchange and Transport of Gases

Gases diffuse based on Partial Pressure ($p$).

• $O_2$ Transport: 97% by RBCs (Oxyhaemoglobin), 3% dissolved in plasma.
  • Oxygen Dissociation Curve: Sigmoid shaped. Shifts to the Right (Dissociation) under: High $pCO_2$, High $H^+$ (Low $pH$), High Temperature.
• $CO_2$ Transport: 70% as Bicarbonate ($HCO_3^-$), 20-25% as Carbamino-haemoglobin, 7% dissolved in plasma.
  • Chloride Shift (Hamburger Phenomenon): Movement of $Cl^-$ into RBCs to maintain ionic balance when $HCO_3^-$ leaves.

3.4 Regulation of Respiration

• Respiratory Rhythm Centre: Located in Medulla.
• Pneumotaxic Centre: Located in Pons; "switch off" point for inspiration.
• Chemosensitive Area: Adjacent to rhythm centre; highly sensitive to $CO_2$ and $H^+$. Role of $O_2$ is insignificant.

4. Body Fluids and Circulation

Blood and Lymph are the vital fluids facilitating transport.

4.1 Formed Elements

1. Erythrocytes (RBCs): 5-5.5 million/$mm^3$. Life span: 120 days.
2. Leucocytes (WBCs): 6000-8000/$mm^3$.
   • Granulocytes: Neutrophils (Phagocytic), Eosinophils (Infections/Allergy), Basophils (Inflammation - Secrete Histamine, Heparin, Serotonin).
   • Agranulocytes: Lymphocytes (Immunity), Monocytes (Phagocytic).
3. Platelets: 1.5 to 3.5 lakh/$mm^3$. Involved in coagulation.

4.2 Blood Grouping and Coagulation

• ABO grouping: Based on antigens A and B on RBC surface. Group O is Universal Donor; Group AB is Universal Recipient.

• Rh Incompatibility: Erythroblastosis Foetalis occurs when an Rh-ve mother carries an Rh+ve fetus (2nd pregnancy). Prevention: Administer anti-Rh antibodies to mother immediately after 1st delivery.

• Coagulation (Clotting): Prothrombin $\xrightarrow{Thrombokinase}$ Thrombin.
  Fibrinogen $\xrightarrow{Thrombin}$ Fibrin. Calcium ($Ca^{2+}$) is essential for clotting.

4.3 Human Circulatory System

• Heart Structure: 4-chambered. Myogenic.
• Cardiac Cycle: 0.8 seconds.
  1. Joint Diastole (0.4s)
  2. Atrial Systole (0.1s)
  3. Ventricular Systole (0.3s)
• Cardiac Output: $Stroke Volume \times Heart Rate = 70 mL \times 72 bpm \approx 5 Litres/min$.

4.4 The ECG (Electrocardiogram)

• P-wave: Atrial Depolarisation (contraction).
• QRS Complex: Ventricular Depolarisation.
• T-wave: Ventricular Repolarisation (return to normal).

5. Excretory Products and Their Elimination

This chapter focuses on removing nitrogenous wastes ($NH_3$, Urea, Uric Acid) and maintaining osmoregulation.

5.1 The Human Excretory System

• Nephron: Structural and functional unit.
  1. Cortical Nephrons: Short Loop of Henle, most common (85%).
  2. Juxtamedullary Nephrons: Long Loop of Henle, runs deep into medulla (15%).

5.2 Urine Formation

Three steps:

1. Glomerular Filtration: Non-selective. GFR = 125 mL/min.
2. Reabsorption: Nearly 99% of filtrate is reabsorbed.
3. Secretion: $H^+$, $K^+$, and $NH_3$ are secreted into the tubule to maintain $pH$.

5.3 Mechanism of Concentration of Filtrate

The Counter-Current Mechanism:

• Operated by Henle's Loop and Vasa Recta.
• The proximity and counter-current flow create an increasing osmolarity towards the inner medullary interstitium ($300 \rightarrow 1200 mOsmol/L$).
• This gradient is mainly caused by $NaCl$ and Urea.

5.4 Regulation: The RAAS Pathway

When GFR falls:

1. JG Cells release Renin.
2. Renin converts Angiotensinogen in blood to Angiotensin I and then Angiotensin II.
3. Angiotensin II (Vasoconstrictor) increases BP and triggers Aldosterone release (increases $Na^+$ and water reabsorption).
4. ANF (Atrial Natriuretic Factor): Opposes RAAS; causes vasodilation to decrease BP.

6. Locomotion and Movement

Movement is a significant characteristic of living beings; Locomotion is the voluntary movement for change in place.

6.1 Muscle Anatomy and Contraction

• Myofibril: Contains Actin (Thin) and Myosin (Thick) filaments.
• Sarcomere: Functional unit between two Z-lines.
• Sliding Filament Theory:
  1. Neural signal reaches NMJ $\rightarrow$ Release of Acetylcholine.
  2. $Ca^{2+}$ released from Sarcoplasmic Reticulum.
  3. $Ca^{2+}$ binds to Troponin $\rightarrow$ Unmasks active sites on Actin.
  4. Myosin head binds to Actin using ATP $\rightarrow$ Cross-bridge formation.
  5. Actin slides over Myosin $\rightarrow$ Sarcomere shortens (I-band reduces, H-zone disappears, A-band remains same).

6.2 The Skeletal System (206 Bones)

• Axial Skeleton (80): Skull (22), Hyoid (1), Ossicles (6), Vertebral Column (26), Sternum (1), Ribs (24).
• Appendicular Skeleton (126): Pectoral girdle, Limbs, Pelvic girdle.

Vertebral Formula: $C_7 T_{12} L_5 S_{(5)} Co_{(4)}$.

6.3 Joints

• Fibrous: Immovable (Skull sutures).
• Cartilaginous: Limited movement (Vertebrae).
• Synovial: Freely movable.
  • Ball and Socket: Shoulder/Hip.
  • Hinge: Knee/Elbow.
  • Pivot: Atlas/Axis.
  • Gliding: Carpals.
  • Saddle: Carpals/Metacarpal of thumb.

7. Neural Control and Coordination

The neural system provides an organized network of point-to-point connections for quick coordination.

7.1 Nerve Impulse Generation

• Resting Potential: High $K^+$ inside, High $Na^+$ outside. Membrane is polarized ($-70 mV$).
• Action Potential: Triggered by stimulus. $Na^+$ channels open $\rightarrow$ $Na^+$ influx $\rightarrow$ Depolarisation ($+30 mV$).
• Repolarisation: $Na^+$ channels close, $K^+$ channels open $\rightarrow$ $K^+$ efflux $\rightarrow$ Resting potential restored.

7.2 Central Nervous System (CNS)

• Forebrain: Cerebrum (Intelligence), Thalamus (Relay), Hypothalamus (Homeostasis, Urge for eating/drinking).
• Midbrain: Corpora Quadrigemina (Reflexes).
• Hindbrain: Cerebellum (Balance), Pons (Pneumotaxic center), Medulla (Respiratory/Cardiac centers).

7.3 Sensory Organs (Briefly for NEET)

• Eye: Retina contains Rods (Scotopic/Night) and Cones (Photopic/Day/Color). Fovea is the point of greatest visual acuity.
• Ear: Organ of Corti is the actual hearing organ. Semicircular canals and Otolith organ maintain body balance (Static and Dynamic).

8. Chemical Coordination and Integration

Endocrine glands are ductless glands that secrete hormones directly into the blood.

8.1 The Master Glands

• Hypothalamus: Secretes Releasing/Inhibiting hormones.
• Pituitary (Hypophysis):
  • Adenohypophysis: GH, PRL, TSH, ACTH, LH, FSH.
  • Neurohypophysis: Stores and releases Oxytocin and Vasopressin (ADH) produced by hypothalamus.

8.2 Major Hormones and Functions

1. Thyroid: Thyroxine ($T_4$, $T_3$) regulates BMR. Requires Iodine.
2. Parathyroid: PTH increases blood $Ca^{2+}$ (Hypercalcemic).
3. Adrenal Cortex: Cortisol (Glucocorticoid) and Aldosterone (Mineralocorticoid).
4. Adrenal Medulla: Adrenaline/Noradrenaline (Emergency hormones).
5. Pancreas: Insulin (Beta cells - decreases glucose); Glucagon (Alpha cells - increases glucose).
6. Gonads: Androgens (Testes); Estrogen/Progesterone (Ovary).

8.3 Mechanism of Hormone Action

• Water-soluble hormones (Protein, Amino-acid derivatives): Bind to membrane receptors, generate Second Messengers (cAMP, $IP_3$, $Ca^{2+}$).
• Lipid-soluble hormones (Steroids, Iodothyronines): Cross membrane, bind to Intracellular receptors, directly affect Gene Expression.

9. Comprehensive Comparison Tables

Table 9.1: Types of Nitrogenous Wastes

Table 9.2: Hormone Solubility and Mechanisms

10. Worked Example Problems

Example 1: Cardiac Output Calculation Question: A person has a heart rate of 80 beats per minute and a stroke volume of 80 mL. Calculate the Cardiac Output. Working: $CO = HR \times SV$ $CO = 80 \times 80 = 6400 mL/min$ Answer: 6.4 Litres/min.

Example 2: GFR and Urine Formation Question: If GFR is 125 mL/min, and the daily urine output is 1.5 Litres, what percentage of filtrate is reabsorbed? Working: Total filtrate per day = $125 \times 60 \times 24 = 180,000 mL = 180 Litres$. Urine excreted = 1.5 Litres. Reabsorbed = $180 - 1.5 = 178.5 Litres$. % Reabsorbed = $(178.5 / 180) \times 100 \approx 99.16%$.

11. Mnemonics for Recall

1. Essential Amino Acids: "PVT TIM HALL" (Phenylalanine, Valine, Threonine, Tryptophan, Isoleucine, Methionine, Histidine, Arginine, Leucine, Lysine).
2. Layers of Adrenal Cortex: "GFR" (Outer to Inner: Glomerulosa, Fasciculata, Reticularis) - Secretes Salt, Sugar, Sex hormones respectively.
3. WBC Count Priority: "Never Let Monkeys Eat Bananas" (Neutrophils > Lymphocytes > Monocytes > Eosinophils > Basophils).
4. Carpal Bones: "She Looks Too Pretty Try To Catch Her" (Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate).

12. NEET Cheat Sheet: Key Stats & Facts

• P50 value: The $pO_2$ at which $Hb$ is 50% saturated (~26-27 mmHg).
• Bohr Effect: Low $pH$ leads to $Hb$ releasing $O_2$.
• Haldane Effect: $O_2$ binding to $Hb$ leads to $CO_2$ release.
• Vital Capacity: Best indicator of respiratory health.
• Double Circulation: Found in Crocodiles, Birds, and Mammals.
• Juxtaglomerular Apparatus (JGA): Formed by distal convoluted tubule and the afferent arteriole.
• Red Muscle vs. White Muscle: Red has high myoglobin and mitochondria (aerobic); White has less myoglobin and more sarcoplasmic reticulum (anaerobic).
• Blind Spot: Optic nerve leaves eye; no photoreceptors.

13. Solved NEET MCQs (Practice Set)

Q1. Which of the following is the correct dental formula for a human child (milk teeth)? A) 2123/2123 B) 2102/2102 C) 2120/2120 D) 0023/0023 Answer: B (Premolars are absent in the primary dentition of humans).

Q2. The partial pressure of $O_2$ in the alveoli of the lungs is: A) Equal to that in blood B) Less than that in blood C) More than that in blood D) Less than that of $CO_2$ Answer: C (Allows $O_2$ to diffuse from alveoli into blood).

Q3. Serum differs from blood in: A) Lacking globulins B) Lacking albumins C) Lacking clotting factors D) Lacking antibodies Answer: C (Serum = Plasma - Clotting factors).

Q4. The peptide hormone that stimulates the secretion of pancreatic enzymes and bile juice is: A) Gastrin B) Secretin C) CCK D) GIP Answer: C (Cholecystokinin stimulates gallbladder and pancreas).

Q5. The pivot joint between Atlas and Axis is a type of: A) Cartilaginous joint B) Synovial joint C) Saddle joint D) Fibrous joint Answer: B (Specifically a pivot synovial joint).

Q6. Identify the correct statement regarding hormone action: A) Steroid hormones enter target cells and bind to intracellular receptors. B) Protein hormones cross the cell membrane easily. C) cAMP is the second messenger for Estrogen. D) All hormones require a cell surface receptor. Answer: A.

(...Remaining 34 questions would follow similar patterns covering all chapters...)

14. Exam Strategy & Common Traps

1. Graph Analysis: Always check the axes for the Oxygen Dissociation Curve. A shift to the right means lower affinity.
2. The "Insignificant" Oxygen: Remember, in the chemical regulation of respiration, $O_2$ plays a very minor role compared to $CO_2$.
3. Muscle Contraction: Many students confuse which bands change length. Remember: "A is for Always Same." Only I-band and H-zone shorten.
4. Hormonal Origins: Don't confuse the storage site with the synthesis site for Oxytocin and Vasopressin. They are made in the Hypothalamus, not the Posterior Pituitary.
5. Excretion: Reabsorption of water in the PCT is obligatory, while in the DCT, it is facultative (controlled by ADH).

15. Final Revision Checklist

Digestion

• Dental formula of adult vs child.
• Layers of the gut wall.
• Role of $HCl$ in activating Pepsinogen.
• Functions of Succus Entericus.
• Difference between Marasmus and Kwashiorkor.

Breathing

• Muscles involved in quiet vs. forced breathing.
• Lung volume values (TV, IRV, ERV, RV).
• $pO_2$ and $pCO_2$ table.
• Factors shifting the $O_2$ curve to the right.
• Role of the Pneumotaxic centre.

Circulation

• Components of plasma and formed elements.
• The blood clotting cascade and $Ca^{2+}$.
• Cardiac cycle timings (0.1s, 0.3s, 0.4s).
• ECG wave interpretation.
• Portal system (Hepatic and Hypophyseal).

Excretion

• Parts of the nephron and their functions.
• Difference between Cortical and Juxtamedullary nephrons.
• Counter-current mechanism (simplified version).
• RAAS mechanism steps.
• Disorders (Uremia, Calculus, Glomerulonephritis).

Locomotion

• Structure of Actin and Myosin.
• Sliding Filament Theory steps.
• Major bones (Skull, Ribs totals).
• Types of Synovial joints and examples.
• Myasthenia gravis vs. Muscular dystrophy.

Neural Control

• Ions involved in Resting/Action potential.
• Functions of Thalamus and Hypothalamus.
• Reflex arc components.
• Middle ear bones (Malleus, Incus, Stapes).
• Organ of Corti location (Basilar membrane).

Chemical Coordination

• Pituitary hormones and target organs.
• Thyroid disorders (Goitre, Exophthalmic goitre).
• Adrenal cortex vs. Medulla hormones.
• Insulin vs. Glucagon functions.
• Mechanism of action: Steroid vs. Protein hormones.

End of Notes. Aim for 360/360 in Biology by mastering these physiological concepts!

Digestion & Absorption — Full Chapter

Digestion is the process of conversion of complex, non-diffusible food substances into simple, absorbable forms. In humans, this is achieved by a combination of mechanical processes (mastication, churning) and biochemical processes (enzymatic hydrolysis).

1. Anatomy of the Alimentary Canal

The human alimentary canal is a continuous muscular tube extending from the mouth to the anus, measuring approximately 6–9 meters in a living adult.

A. The Oral Cavity and Dentition

The mouth leads to the buccal cavity, which contains the tongue and teeth.

• Thecodont: Teeth are embedded in sockets of the jaw bone.
• Diphyodont: Two sets of teeth during the lifetime (deciduous/milk teeth and permanent teeth).
• Heterodont: Different types of teeth—Incisors ($I$), Canines ($C$), Premolars ($PM$), and Molars ($M$).

The Dental Formula: The arrangement of teeth in each half of the upper and lower jaw is represented by: $$\text{Dental Formula} = \frac{I, C, PM, M}{I, C, PM, M}$$

• Child (Milk teeth): $\frac{2, 1, 0, 2}{2, 1, 0, 2} \times 2 = 20$ (Premolars are absent).
• Adult: $\frac{2, 1, 2, 3}{2, 1, 2, 3} \times 2 = 32$.

B. Histology of the Gut Wall

From the esophagus to the rectum, the gut wall consists of four distinct layers:

1. Serosa: The outermost layer made of thin mesothelium and connective tissue. (Adventitia in the esophagus).
2. Muscularis: Smooth muscles arranged into an inner circular and outer longitudinal layer. An oblique muscle layer is uniquely present in the stomach.
3. Submucosa: Loose connective tissue containing nerves (Meissner’s plexus), blood, and lymph vessels. In the duodenum, Brunner’s glands are located here.
4. Mucosa: The innermost lining. In the stomach, it forms irregular folds called rugae. In the small intestine, it forms villi.

2. The Digestive Glands

A. Salivary Glands

Three pairs contribute to saliva production:

• Parotids: Near the cheek (largest).
• Sub-maxillary/Sub-mandibular: At the lower jaw.
• Sub-linguals: Below the tongue. Saliva contains Salivary Amylase (Ptyalin) ($pH \approx 6.8$), electrolytes ($Na^+, K^+, Cl^-, HCO_3^-$), and Lysozyme (antibacterial).

B. Gastric Glands

Located in the mucosa of the stomach, these glands contain four major cell types:

1. Mucus neck cells: Secrete mucus to protect the lining.
2. Peptic/Chief/Zymogenic cells: Secrete proenzymes pepsinogen and prorennin.
3. Parietal/Oxyntic cells: Secrete HCl (provides $pH$ 1.8) and Intrinsic Factor (essential for $Vitamin B_{12}$ absorption).
4. G-cells: Endocrine cells that secrete Gastrin to stimulate gastric juice secretion.

C. The Pancreas

A heterocrine gland situated between the limbs of the U-shaped duodenum.

• Exocrine part: Secretes alkaline pancreatic juice ($pH \approx 8.4$).
• Endocrine part: Islets of Langerhans secrete Insulin and Glucagon.

D. The Liver and Gallbladder

The liver is the largest gland ($1.2 - 1.5$ kg). Its structural units are hepatic lobules covered by Glisson’s capsule.

• Bile: Secreted by hepatic cells, stored in the gallbladder. It contains bile salts (sodium glycocholate/taurocholate), bile pigments (bilirubin, biliverdin), and cholesterol. Bile contains NO enzymes.

3. The Physiology of Digestion

A. Digestion in the Mouth

Salivary amylase acts on starch: $$\text{Starch} \xrightarrow[\text{pH 6.8}]{\text{Salivary Amylase}} \text{Maltose (Disaccharide)}$$ Note: Only 30% of starch is hydrolyzed here.

B. Digestion in the Stomach

Food is mixed with gastric juice to form Chyme.

1. HCl converts inactive pepsinogen into active pepsin.
2. Proteins $\xrightarrow{\text{Pepsin}}$ Proteoses + Peptones.
3. Rennin (in infants) $\xrightarrow{}$ Digestion of milk protein (Casein).

C. Digestion in the Small Intestine

The chyme meets three secretions: Bile, Pancreatic juice, and Intestinal juice.

I. Action of Pancreatic Juice:

• Trypsinogen is activated by Enterokinase (from intestinal mucosa) into Trypsin.
• Proteins/Peptones $\xrightarrow{\text{Trypsin/Chymotrypsin/Carboxypeptidase}}$ Dipeptides.
• Polysaccharides (Starch) $\xrightarrow{\text{Amylase}}$ Disaccharides.
• Fats $\xrightarrow{\text{Lipases}}$ Diglycerides $\rightarrow$ Monoglycerides.
• Nucleic Acids $\xrightarrow{\text{Nucleases}}$ Nucleotides.

II. Action of Succus Entericus (Intestinal Juice): This final step converts biopolymers into their simplest absorbable units:

• Dipeptides $\xrightarrow{\text{Dipeptidases}}$ Amino Acids
• Maltose $\xrightarrow{\text{Maltase}}$ Glucose + Glucose
• Lactose $\xrightarrow{\text{Lactase}}$ Glucose + Galactose
• Sucrose $\xrightarrow{\text{Sucrase}}$ Glucose + Fructose
• Nucleotides $\xrightarrow{\text{Nucleotidases}}$ Nucleosides $\xrightarrow{\text{Nucleosidases}}$ Sugars + Bases
• Di/Monoglycerides $\xrightarrow{\text{Lipases}}$ Fatty acids + Glycerol

4. Comprehensive Enzyme Cascade Table

5. Absorption of Digested Products

Absorption is the process by which end products pass through the intestinal mucosa into the blood or lymph.

Fat Absorption (Unique Mechanism): Fatty acids and Glycerol are insoluble and cannot enter the blood directly.

1. They are incorporated into small droplets called Micelles.
2. Micelles move into intestinal mucosa cells.
3. They are reformed into very small protein-coated fat globules called Chylomicrons.
4. Chylomicrons are transported into lymph vessels (Lacteals) in the villi.
5. Lacteals eventually release them into the bloodstream.

6. Disorders of the Digestive System

• Jaundice: Liver is affected, skin and eyes turn yellow due to the deposit of bile pigments.
• Vomiting: Ejection of stomach contents through the mouth; controlled by the vomit center in the medulla.
• Diarrhoea: Abnormal frequency of bowel movement and increased liquidity of feces; reduces absorption of food.
• Constipation: Feces are retained within the colon as bowel movements occur irregularly.
• Indigestion: Food is not properly digested, leading to a feeling of fullness. Causes: anxiety, food poisoning, overeating, spicy food.

Protein-Energy Malnutrition (PEM):

1. Marasmus: Deficiency of both Proteins and Calories. Affects infants under 1 year. Symptoms: extreme emaciation, thinning of limbs, dry/wrinkled skin.
2. Kwashiorkor: Deficiency of Protein ONLY (calorie intake may be adequate). Affects children over 1 year. Symptoms: Wasting of muscles, thinning of limbs, but unlike Marasmus, some fat is left under the skin and extensive oedema (swelling) is observed.

Solved NEET MCQs (High-Yield)

Q1. A person who is eating boiled potato, what will be the constituent of the food? A) Cellulose and Starch B) Starch only C) Lactose and Protein D) DNA and RNA Answer: B. Explanation: Potatoes are primarily composed of starch. Cellulose is present in the cell wall, but humans cannot digest it. Starch digestion begins in the mouth by salivary amylase.

Q2. Which of the following cells in the gastric glands secrete Intrinsic Factor? A) Peptic cells B) Zymogenic cells C) Parietal cells D) Mucus neck cells Answer: C. Explanation: Parietal or Oxyntic cells secrete $HCl$ and Castle's Intrinsic Factor, which is essential for the absorption of $Vitamin B_{12}$ in the ileum.

Q3. The enzyme Enterokinase helps in the conversion of: A) Caseinogen into Casein B) Trypsinogen into Trypsin C) Pepsinogen into Pepsin D) Proteins into Polypeptides Answer: B. Explanation: Enterokinase is secreted by the intestinal mucosa. It is a non-digestive enzyme that acts as a trigger to activate the pancreatic enzyme Trypsinogen into Trypsin.

Q4. Carrier proteins facilitate the absorption of: A) Fructose and some amino acids B) Fatty acids and Glycerol C) Glucose and Fatty acids D) Fructose and $Cl^-$ ions Answer: A. Explanation: Facilitated diffusion requires a carrier protein. Fructose is the classic example in NEET for this process.

Q5. Choose the correct dental formula for a human child of 3 years. A) 2123 / 2123 B) 2102 / 2102 C) 2120 / 2120 D) 0023 / 0023 Answer: B. Explanation: Children lack the two pairs of premolars and the third molar (wisdom tooth). Thus, the formula is 2102/2102.

Q6. What happens to the pH of chyme when it enters the duodenum? A) Becomes more acidic B) Stays at pH 1.8 C) Becomes alkaline D) Drops to pH 5.0 Answer: C. Explanation: Chyme from the stomach is highly acidic (pH 1.8). In the duodenum, bicarbonate ions from the pancreas and bile neutralize it, bringing the pH to about 7.8–8.4, which is optimal for pancreatic enzymes.

Q7. Which of the following is NOT a component of bile? A) Bilirubin B) Phospholipids C) Lipase D) Cholesterol Answer: C. Explanation: Bile contains no enzymes. Lipase is a pancreatic and intestinal enzyme. Bile only aids lipase by emulsifying fats.

Q8. A patient presents with thinning of limbs, dry skin, and extreme emaciation. He is 6 months old. He is likely suffering from: A) Kwashiorkor B) Marasmus C) Jaundice D) Pellagra Answer: B. Explanation: The age (under 1 year) and the deficiency of both calories and proteins indicate Marasmus. Kwashiorkor occurs in older children and presents with edema.

Mnemonic for Histology Layers (Outside to Inside): Some Men Sleep Much

• Serosa
• Muscularis
• Submucosa
• Mucosa

Breathing & Exchange of Gases

Respiration is the metabolic process by which the living cells of an organism produce energy (ATP) by the oxidation of complex organic substances. In humans, this involves two distinct but integrated processes: Breathing (Physical exchange of gases) and Cellular Respiration (Chemical breakdown of nutrients).

I. Respiratory Organs: A Comparative Glance

Evolution of respiratory organs depends primarily on the habitats and levels of organization of the animals.

The Human Respiratory System Path: External Nostrils $\rightarrow$ Nasal passage $\rightarrow$ Nasal Chamber $\rightarrow$ Pharynx (Common passage) $\rightarrow$ Larynx (Sound box) $\rightarrow$ Trachea (Wind pipe) $\rightarrow$ Primary, Secondary, Tertiary Bronchi $\rightarrow$ Bronchioles $\rightarrow$ Terminal Bronchioles $\rightarrow$ Alveoli (Functional unit).

• Conducting Part: Up to terminal bronchioles. Function: Transports atmospheric air, clears it from foreign particles, humidifies, and brings air to body temperature.
• Respiratory (Exchange) Part: Alveoli and their ducts. Function: Actual diffusion of $O_2$ and $CO_2$ between blood and atmospheric air.

II. Mechanism of Breathing: The Physics of Respiration

Breathing involves two stages: Inspiration (atmospheric air is drawn in) and Expiration (alveolar air is released out). This movement of air is governed by Boyle’s Law: $P \propto \frac{1}{V}$ (at constant temperature).

1. Inspiration (Active Process)

Inspiration occurs if the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure (negative pressure).

• Diaphragm contracts: Moves downward (increases thoracic volume in the antero-posterior axis).
• External Intercostal Muscles (EICM) contract: Lifts ribs and sternum (increases thoracic volume in the dorso-ventral axis).
• Result: Overall thoracic volume $\uparrow$ $\rightarrow$ Intra-pulmonary volume $\uparrow$ $\rightarrow$ Intra-pulmonary pressure $\downarrow$ (below atmospheric). Air rushes into the lungs.

2. Expiration (Passive Process)

Expiration occurs when intra-pulmonary pressure is higher than atmospheric pressure.

• Diaphragm relaxes: Returns to dome shape (decreases thoracic volume).
• EICM relaxes: Ribs move downward and inward.
• Result: Thoracic volume $\downarrow$ $\rightarrow$ Intra-pulmonary volume $\downarrow$ $\rightarrow$ Intra-pulmonary pressure $\uparrow$. Air is expelled out.

Note: We can increase the strength of expiration with the help of Abdominal muscles and Internal Intercostal Muscles (IICM). The average breathing rate is 12–16 times/minute.

III. Respiratory Volumes and Capacities

Understanding these values is crucial for clinical diagnosis using a Spirometer (Note: Residual Volume cannot be measured by a spirometer).

A. Respiratory Volumes (Standard values for a healthy adult male)

1. Tidal Volume (TV): Volume of air inspired or expired during a normal respiration.
   • Value: $\approx 500$ mL (or $6000–8000$ mL per minute).
2. Inspiratory Reserve Volume (IRV): Additional volume of air a person can inspire by a forcible inspiration.
   • Value: $2500$ mL to $3000$ mL.
3. Expiratory Reserve Volume (ERV): Additional volume of air a person can expire by a forcible expiration.
   • Value: $1000$ mL to $1100$ mL.
4. Residual Volume (RV): Volume of air remaining in the lungs even after a forcible expiration.
   • Value: $1100$ mL to $1200$ mL.

B. Respiratory Capacities (Derived values)

1. Inspiratory Capacity (IC): Total volume of air a person can inspire after a normal expiration.
   • Formula: $IC = TV + IRV$
   • Value: $\approx 3500$ mL.
2. Expiratory Capacity (EC): Total volume of air a person can expire after a normal inspiration.
   • Formula: $EC = TV + ERV$
   • Value: $\approx 1600$ mL.
3. Functional Residual Capacity (FRC): Volume of air that will remain in the lungs after a normal expiration.
   • Formula: $FRC = ERV + RV$
   • Value: $\approx 2300$ mL.
4. Vital Capacity (VC): The maximum volume of air a person can breathe in after a forced expiration or the maximum air a person can breathe out after a forced inspiration.
   • Formula: $VC = ERV + TV + IRV$
   • Value: $\approx 4600$ mL.
5. Total Lung Capacity (TLC): Total volume of air accommodated in the lungs at the end of a forced inspiration.
   • Formula: $TLC = RV + ERV + TV + IRV$ OR $TLC = VC + RV$
   • Value: $\approx 5800$ mL.

IV. Exchange of Gases

Gases diffuse across the Respiratory Membrane based on Partial Pressure ($p$) gradients. Diffusion depends on:

1. Pressure/Concentration gradient.
2. Solubility of gases ($CO_2$ is 20-25 times more soluble than $O_2$).
3. Thickness of the diffusion membrane.

The Diffusion Membrane Composition:

1. Thin squamous epithelium of alveoli.
2. Endothelium of alveolar capillaries.
3. Basement substance between them. Total thickness is less than 1 mm.

V. Transport of $O_2$

About 97% of $O_2$ is transported by RBCs in the blood as Oxyhaemoglobin, and the remaining 3% is carried in a dissolved state through the plasma.

The Oxygen-Haemoglobin Dissociation Curve

This is a Sigmoid (S-shaped) curve obtained when percentage saturation of haemoglobin with $O_2$ is plotted against the $pO_2$.

Factors affecting the curve:

• Shift to the Right (Decreased affinity, $O_2$ dissociation/unloading at tissues):
  • $\uparrow pCO_2$
  • $\downarrow pH$ (High $H^+$ concentration) — This is known as the Bohr Effect.
  • $\uparrow$ Temperature.
  • $\uparrow$ 2,3-BPG (Bisphosphoglycerate).
• Shift to the Left (Increased affinity, $O_2$ binding/loading at Alveoli):
  • $\uparrow pO_2$
  • $\downarrow pCO_2$
  • $\uparrow pH$ (Low $H^+$)
  • $\downarrow$ Temperature.

Numerical Significance: Every $100$ mL of oxygenated blood can deliver around $5$ mL of $O_2$ to the tissues under normal physiological conditions.

VI. Transport of $CO_2$

$CO_2$ is transported in three forms:

1. As Bicarbonate ($\approx 70%$): The major form.
2. As Carbamino-haemoglobin ($\approx 20-25%$): Bound to the amino groups of haemoglobin.
3. Dissolved in Plasma ($\approx 7%$): Due to higher solubility.

The Bicarbonate Mechanism & Chloride Shift

In RBCs, an enzyme called Carbonic Anhydrase facilitates the following reaction: $$CO_2 + H_2O \xrightleftharpoons{Carbonic\ Anhydrase} H_2CO_3 \xrightleftharpoons{Carbonic\ Anhydrase} HCO_3^- + H^+$$

1. At Tissues: $pCO_2$ is high. $CO_2$ diffuses into RBCs, forms $HCO_3^-$. The $HCO_3^-$ diffuses out of the RBC into the plasma. To maintain ionic balance, Chloride ions ($Cl^-$) move from plasma into the RBC. This is called the Chloride Shift or Hamburger Phenomenon.
2. At Alveoli: $pCO_2$ is low. The reaction reverses. $HCO_3^-$ enters RBC, $Cl^-$ moves out (Reverse Chloride Shift). $CO_2$ is regenerated and released.

Numerical Significance: Every $100$ mL of deoxygenated blood delivers approximately $4$ mL of $CO_2$ to the alveoli.

VII. Regulation of Respiration

Humans possess a significant ability to maintain and moderate the respiratory rhythm to suit the demands of the body tissues via the neural system.

1. Respiratory Rhythm Centre: Located in the Medulla oblongata. Primary center responsible for regulation.
2. Pneumotaxic Centre: Located in the Pons varolii. It acts as a "switch-off" point for inspiration. It can reduce the duration of inspiration and thereby alter the respiratory rate.
3. Chemosensitive Area: Situated adjacent to the rhythm center. Highly sensitive to $CO_2$ and $H^+$ ions. High levels activate this center, which signals the rhythm center to eliminate these substances.
4. Receptors in Aortic Arch & Carotid Artery: Recognize changes in $CO_2$ and $H^+$ concentration and send signals to the rhythm center.
   • Crucial Point: The role of Oxygen in the regulation of respiratory rhythm is quite insignificant.

VIII. Disorders of the Respiratory System

1. Asthma: Difficulty in breathing causing wheezing due to inflammation of bronchi and bronchioles.
2. Emphysema: A chronic disorder where alveolar walls are damaged, resulting in decreased respiratory surface area. One of the major causes is cigarette smoking.
3. Occupational Respiratory Disorders (ORD): In certain industries involving grinding or stone-breaking (silica, asbestos), long-term exposure leads to proliferation of fibrous tissues (fibrosis), causing serious lung damage. Examples: Silicosis, Asbestosis.

IX. Mnemonics for Recall

1. Shifting the Curve to the Right (CADET, face Right!):

   • C - $CO_2$ (High)
   • A - Acid/low pH ($H^+$ High)
   • D - 2,3-DPG (High)
   • E - Exercise
   • T - Temperature (High)
   • Mnemonic meaning: All these factors increase, causing the curve to shift Right (unloading $O_2$).

2. Respiratory Capacities Hierarchy:

   • TLC > VC > IC > FRC > EC
   • Remember: "Tall Vishal Is Feeding Elephants"

X. Solved MCQs (NEET Pattern)

Q1. The maximum volume of air a person can breathe in after a forced expiration is: A. $TV + IRV$ B. $TV + ERV$ C. $TV + IRV + ERV$ D. $TV + IRV + RV$ Answer: C. Explanation: This defines Vital Capacity (VC).

Q2. Which of the following factors is NOT favorable for the formation of oxyhaemoglobin at the alveolar level? A. High $pO_2$ B. Low $pCO_2$ C. High $H^+$ concentration D. Low temperature Answer: C. Explanation: High $H^+$ (low pH) favors dissociation (Oxygen release), not formation.

Q3. Approximately what percentage of $CO_2$ is transported as bicarbonates? A. 7% B. 20-25% C. 70% D. 97% Answer: C. Explanation: 7% is dissolved, 20-25% as carbamino-haemoglobin, and 70% as bicarbonate.

Q4. What is the value of $pCO_2$ in deoxygenated blood? A. 40 mmHg B. 45 mmHg C. 95 mmHg D. 104 mmHg Answer: B. Explanation: $pCO_2$ is 45 mmHg in deoxygenated blood and tissues.

Q5. The Pneumotaxic centre is located in: A. Medulla oblongata B. Cerebrum C. Pons D. Cerebellum Answer: C.

Q6. Emphysema is a condition characterized by: A. Inflammation of bronchioles B. Fibrosis of lungs C. Damage to alveolar walls D. Spasm in tracheal muscles Answer: C.

Q7. If a person's TV = 500ml, IRV = 2500ml, and ERV = 1000ml, what is their Vital Capacity? A. 3000 ml B. 4000 ml C. 4200 ml D. 1500 ml Answer: B. Explanation: $VC = TV + IRV + ERV = 500 + 2500 + 1000 = 4000$ mL.

Q8. The Chloride Shift occurs in response to the movement of: A. $K^+$ into the plasma B. $HCO_3^-$ out of the RBC C. $H^+$ into the RBC D. $Na^+$ into the plasma Answer: B. Explanation: As bicarbonate leaves the RBC, chloride enters to maintain electrochemical neutrality.

Q9. Carbonic anhydrase enzyme is found in high concentration in: A. Plasma B. Lymphocytes C. RBCs D. Platelets Answer: C.

Q10. What happens to the breathing rate when the $CO_2$ concentration in blood increases? A. It decreases B. It stops C. It increases D. No effect Answer: C. Explanation: Higher $CO_2$ lowers pH, signaling the Medullary rhythm center to increase the rate of breathing to expel $CO_2$.

Body Fluids & Circulation

In complex organisms, simple diffusion is insufficient for the transport of nutrients, gases, and waste. Evolution has favored the development of specialized fluids—Blood and Lymph—and a muscular pump, the Heart, to ensure efficient bulk flow.

1. Composition of Blood

Blood is a fluid connective tissue consisting of a fluid matrix, plasma, and formed elements.

A. Plasma (55% of Blood)

Plasma is a straw-colored, viscous fluid. It is composed of:

• Water (90-92%): The primary solvent.
• Proteins (6-8%):
  • Albumin: Produced by the liver; maintains Blood Colloid Osmotic Pressure (BCOP). Prevents edema.
  • Globulins: Primarily $\gamma$-globulins (antibodies/immunoglobulins) involved in defense mechanisms.
  • Fibrinogen: Large protein synthesized by the liver; essential for blood clotting.
• Nutrients & Waste: Glucose, amino acids, lipids, urea, and creatinine.
• Electrolytes: $Na^+$, $Ca^{2+}$, $Mg^{2+}$, $HCO_3^-$, $Cl^-$.

NEET Concept: Serum Serum = Plasma - Clotting Factors. Serum does not clot.

B. Formed Elements (45% of Blood)

Formed elements include Erythrocytes, Leucocytes, and Platelets.

RBC Characteristics:

• Biconcave, enucleated (in mammals, except Camel/Llama) to increase surface area for $O_2$ diffusion and accommodate more Hemoglobin ($\approx 12-16g/100ml$).
• Formed in Red Bone Marrow (Erythropoiesis). Destroyed in the Spleen (Graveyard of RBCs).

WBC Classification:

1. Granulocytes:
   • Neutrophils (60-65%): Phagocytic; first responders.
   • Eosinophils (2-3%): Resist infections; associated with allergic reactions.
   • Basophils (0.5-1%): Secrete Histamine (vasodilator), Serotonin (vasoconstrictor), and Heparin (anticoagulant).
2. Agranulocytes:
   • Lymphocytes (20-25%): B and T cells; responsible for specific immunity.
   • Monocytes (6-8%): Largest WBCs; phagocytic; become macrophages in tissues.

2. Blood Groups and Coagulation

A. ABO System

Based on the presence or absence of two surface antigens (A and B) on the RBCs.

B. Rh Grouping & Erythroblastosis Fetalis

The Rh antigen (discovered in Rhesus monkeys) is present in 80% of humans ($Rh^+$).

Erythroblastosis Fetalis (Hemolytic Disease of the Newborn):

• Condition: $Rh^-$ mother carrying an $Rh^+$ fetus.
• Mechanism: During first delivery, fetal $Rh^+$ blood may mix with maternal blood. Mother develops anti-Rh antibodies.
• Consequence: In subsequent pregnancies, maternal anti-Rh antibodies ($IgG$) cross the placenta and destroy fetal RBCs.
• Result: Severe anemia and jaundice in the baby.
• Prevention: Administering Anti-D antibodies (RhoGAM) to the mother immediately after the first delivery.

C. Blood Coagulation (The Cascade)

Hemostasis occurs via a "Cascade Theory" involving 13 clotting factors.

1. Injury: Tissue damage or platelet rupture.
2. Prothrombinase Formation:
   • Extrinsic Pathway: Fast; triggered by Tissue Thromboplastin (Factor III).
   • Intrinsic Pathway: Slower; triggered by contact with collagen (Factor XII).
3. Prothrombin Conversion: $$\text{Prothrombin} \xrightarrow{\text{Thrombokinase} + Ca^{2+}} \text{Thrombin}$$
4. Fibrin Formation: $$\text{Fibrinogen (Soluble)} \xrightarrow{\text{Thrombin}} \text{Fibrin (Insoluble threads)}$$ Fibrin traps formed elements to form the Clot (Coagulum).

3. Lymphatic System

Lymph is the "middleman" of the body. As blood passes through capillaries, some water and small solutes are filtered into intercellular spaces (interstitial fluid).

• Composition: Similar to plasma but with lower protein content and no RBCs. Rich in Lymphocytes.
• Functions:
  • Returns interstitial fluid to the blood.
  • Absorbs fats via Lacteals (lymph vessels in intestinal villi) as chylomicrons.
  • Immune filtering in lymph nodes.

4. Anatomy of the Human Heart

The heart is a mesodermally derived organ, situated in the thoracic cavity in the mediastinum.

• Pericardium: Double-walled membranous bag protecting the heart.
• Chambers:
  • Two upper thin-walled Atria.
  • Two lower thick-walled Ventricles (Left ventricle is the thickest).
• Valves (Unidirectional Flow):
  • Tricuspid: Between Right Atrium and Right Ventricle.
  • Bicuspid (Mitral): Between Left Atrium and Left Ventricle.
  • Semilunar Valves: Guard the openings of the Pulmonary Artery and Aorta.
• Conducting System:
  • SA Node (Pacemaker): In the upper-right corner of the right atrium. Generates impulses at $70-75/min$.
  • AV Node: Lower-left corner of the right atrium.
  • Bundle of His & Purkinje Fibers: Distribute the impulse to the ventricular musculature.

5. Cardiac Cycle

The cardiac cycle refers to the sequence of events from the beginning of one heartbeat to the beginning of the next. Duration = 0.8 seconds (at 75 bpm).

1. Joint Diastole (0.4s): All four chambers are relaxed. Tricuspid and bicuspid valves are open. Blood from pulmonary veins and vena cava flows into left and right ventricles respectively.
2. Atrial Systole (0.1s): SA node generates action potential. Atria contract. Flow of blood into ventricles increases by $\approx 30%$.
3. Ventricular Systole (0.3s): Ventricles contract. Ventricular pressure rises.
   • AV valves close immediately (Causes $S_1$ - "LUB" sound).
   • Pressure exceeds arterial pressure $\rightarrow$ Semilunar valves open.
   • Blood is ejected into the Aorta and Pulmonary Artery.
4. Ventricular Diastole: Ventricles relax. Ventricular pressure falls.
   • Semilunar valves close (Causes $S_2$ - "DUP" sound).
   • As pressure continues to fall, AV valves re-open.

Cardiac Calculations:

• Stroke Volume (SV): Amount of blood pumped by each ventricle per beat $\approx 70 ml$.
• Cardiac Output (CO): $$CO = \text{Heart Rate} \times \text{Stroke Volume}$$ $$CO = 72 \text{ bpm} \times 70 \text{ ml} = 5040 \text{ ml/min} \approx 5 \text{ Liters/min}$$

6. Electrocardiogram (ECG)

A graphical representation of the electrical activity of the heart during a cardiac cycle. To obtain a standard ECG, a patient is connected with three electrical leads (one on each wrist and one on the left ankle).

• P-Wave: Depolarisation of the atria (leads to atrial contraction).
• QRS Complex: Depolarisation of the ventricles (leads to ventricular contraction). Systole starts shortly after Q.
• T-Wave: Repolarisation of the ventricles (return from excited to normal state). The end of the T-wave marks the end of systole.

Clinical Significance: Deviation in the shape or duration of these waves indicates heart ailments (e.g., Enlarged QRS indicates myocardial infarction).

7. Double Circulation

Humans exhibit complete double circulation, meaning blood passes through the heart twice for every circuit of the body.

1. Pulmonary Circulation: $$\text{Right Ventricle} \rightarrow \text{Pulmonary Artery} \rightarrow \text{Lungs} \rightarrow \text{Pulmonary Veins} \rightarrow \text{Left Atrium}$$
2. Systemic Circulation: $$\text{Left Ventricle} \rightarrow \text{Aorta} \rightarrow \text{Tissues} \rightarrow \text{Vena Cava} \rightarrow \text{Right Atrium}$$
3. Hepatic Portal System: A unique vascular connection between the digestive tract and the liver. Blood from the intestine reaches the liver via the Hepatic Portal Vein before systemic circulation.
4. Coronary Circulation: A special system of blood vessels for the circulation of blood to and from the cardiac musculature.

8. Disorders of the Circulatory System

• Hypertension (High BP): Normal BP is 120/80 mmHg. Hypertension is defined as consistent BP of 140/90 or higher. Leads to heart disease and affects vital organs like brain and kidney.
• Coronary Artery Disease (CAD) / Atherosclerosis: Deposition of Calcium, Fat, Cholesterol, and fibrous tissue in the arteries supplying heart muscle, making the lumen narrower.
• Angina (Angina Pectoris): Acute chest pain when no enough oxygen reaches the heart muscle. Common in middle-aged and elderly.
• Heart Failure: State where the heart is not pumping blood effectively enough to meet the needs of the body. It is often called Congestive Heart Failure because congestion of lungs is a main symptom.
  • Note: Heart failure is NOT heart attack (muscle damage) or cardiac arrest (heart stops beating).

Solved NEET MCQs

Q1. Serum differs from blood in: A. Lacking globulins B. Lacking clotting factors C. Lacking antibodies D. Lacking albumin Answer: B. Serum is plasma minus clotting factors.

Q2. What would be the cardiac output of a person having 72 heartbeats per minute and a stroke volume of 50 ml? A. 360 ml B. 3600 ml C. 7200 ml D. 5000 ml Workings: $CO = HR \times SV = 72 \times 50 = 3600 ml$. Answer: B.

Q3. The 'LUB' sound is produced during: A. Closing of semilunar valves B. Opening of AV valves C. Closing of Tricuspid and Bicuspid valves D. Atrial systole Answer: C. $S_1$ is due to AV valve closure at the start of ventricular systole.

Q4. A person with blood group AB can receive blood from: A. Only AB B. Only O C. Both A and B D. Any group Answer: D. AB is the universal recipient.

Q5. Which of the following is known as the graveyard of RBCs? A. Liver B. Spleen C. Kidney D. Bone marrow Answer: B.

Q6. During erythroblastosis fetalis, which antibody crosses the placenta? A. IgA B. IgM C. IgG D. IgE Answer: C. IgG is the only antibody capable of crossing the placenta.

Q7. The state of heart when it is not pumping blood effectively to meet the body's needs is: A. Heart attack B. Cardiac arrest C. Heart failure D. Angina Answer: C.

Q8. Which wave in ECG represents the end of ventricular systole? A. P-wave B. QRS complex C. T-wave D. End of T-wave Answer: D.

Q9. Identify the correct sequence of the conducting system of the heart: A. AV Node $\rightarrow$ SA Node $\rightarrow$ Bundle of His B. SA Node $\rightarrow$ AV Node $\rightarrow$ Bundle of His $\rightarrow$ Purkinje fibers C. Purkinje fibers $\rightarrow$ AV Node $\rightarrow$ SA Node D. SA Node $\rightarrow$ Purkinje fibers $\rightarrow$ AV Node Answer: B.

Q10. Vitamin essential for blood coagulation is: A. Vitamin A B. Vitamin B C. Vitamin C D. Vitamin K Answer: D. Vitamin K is required for the synthesis of factors II, VII, IX, and X.

Excretory Products & Their Elimination

Nitrogenous waste management is a fundamental homeostatic process. Animals accumulate ammonia, urea, uric acid, carbon dioxide, water, and ions like $Na^+$, $K^+$, $Cl^-$, phosphate, and sulfate through metabolic activities or excessive ingestion. These substances must be removed totally or partially to maintain the internal environment.

1. Modes of Excretion: A Comparative Analysis

Animals are categorized based on their primary nitrogenous waste. This classification is heavily influenced by the availability of water in their habitat.

Key Concept: The Evolutionary Trade-off Ammonia is the first metabolic byproduct of protein metabolism. It is highly soluble and diffuses across body surfaces or gill surfaces as ammonium ions ($NH_4^+$). Because it is toxic, animals that live in water (where water conservation isn't an issue) use it. Terrestrial animals must conserve water, so they convert ammonia into less toxic urea (in the liver via the Ornithine Cycle) or uric acid to reduce water loss.

2. Human Excretory System: Macro and Micro Anatomy

2.1 The Kidney

The human excretory system consists of a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra.

• Location: Retroperitoneal, between the levels of the last thoracic ($T_{12}$) and third lumbar ($L_3$) vertebra.
• Measurements: 10–12 cm length, 5–7 cm width, 2–3 cm thickness. Average weight is 120–170g.
• Internal Structure: The outer layer is a tough capsule. Inside, two zones exist: an outer Cortex and an inner Medulla.
  • The medulla is divided into conical masses called Medullary Pyramids.
  • The cortex extends between pyramids as Columns of Bertin.
  • The Hilum is a notch where the ureter, blood vessels, and nerves enter.

2.2 The Nephron: The Functional Unit

Each kidney contains roughly 1 million nephrons. A nephron consists of two parts: the Glomerulus (a tuft of capillaries) and the Renal Tubule.

Classification of Nephrons:

1. Cortical Nephrons (85%): The Loop of Henle is very short and extends only very little into the medulla.
2. Juxtamedullary Nephrons (15%): The Loop of Henle is very long and runs deep into the medulla. These are crucial for concentrating urine during water scarcity.

3. Mechanism of Urine Formation

Urine formation involves three main processes: Glomerular Filtration, Reabsorption, and Secretion.

3.1 Glomerular Filtration

This is a non-selective process powered by blood pressure.

• Filtration Membrane: Consists of three layers: (1) Endothelium of glomerular blood vessels, (2) Epithelium of Bowman’s capsule (cells called podocytes with filtration slits), and (3) Basement membrane between them.
• GFR (Glomerular Filtration Rate): The amount of filtrate formed by the kidneys per minute.
  • Standard value: $125 \text{ ml/min}$ or $180 \text{ Liters per day}$.
• Net Filtration Pressure (NFP): $$NFP = GHP - (BCOP + CHP)$$ Where $GHP$ is Glomerular Hydrostatic Pressure ($\approx 60$ mmHg), $BCOP$ is Blood Colloid Osmotic Pressure ($\approx 32$ mmHg), and $CHP$ is Capsular Hydrostatic Pressure ($\approx 18$ mmHg). $$NFP = 60 - (32 + 18) = 10 \text{ mmHg}$$

3.2 Tubular Reabsorption

Out of 180L of filtrate, only 1.5L is excreted as urine. Nearly 99% is reabsorbed.

• PCT: Reabsorbs 70-80% of electrolytes and water. 100% of Glucose and Amino acids are reabsorbed here via active transport.
• Henle’s Loop: Minimum reabsorption occurs here. It maintains high osmolarity of medullary interstitial fluid.

3.3 Tubular Secretion

Secreted substances include $H^+$, $K^+$, and $NH_3$ into the filtrate. This is essential for maintaining the ionic and acid-base balance of body fluids.

4. The Counter-Current Mechanism

Humans have the ability to produce urine that is nearly 4 times more concentrated than the initial filtrate (1200 mOsm/L vs 300 mOsm/L). This is achieved by the Henle's Loop and Vasa Recta.

1. Counter-current Flow: The flow of filtrate in the two limbs of Henle’s loop is in opposite directions. Similarly, the flow of blood through the vasa recta is also in a counter-current pattern.
2. Maintaining Gradient:
   • The ascending limb of Henle transports $NaCl$ to the medullary interstitium.
   • $NaCl$ enters the descending limb of the vasa recta and is returned to the interstitium by the ascending limb of the vasa recta.
   • Small amounts of Urea enter the thin segment of the ascending limb and are recycled back to the medullary interstitium by the collecting duct.
3. Result: This "Counter-current Multiplier" creates an increasing osmolarity gradient from the cortex (300 mOsm/L) to the inner medulla (1200 mOsm/L). This gradient allows water to be easily drawn out from the collecting duct by osmosis, concentrating the urine.

5. Regulation of Kidney Function

Kidney function is regulated by the Hypothalamus, JGA, and the Heart.

5.1 ADH (Antidiuretic Hormone / Vasopressin)

• Trigger: Increase in body fluid osmolarity (water loss).
• Action: Osmoreceptors stimulate the Neurohypophysis to release ADH. ADH makes the DCT and Collecting Duct more permeable to water, facilitating reabsorption.
• Feedback: Increase in body fluid volume switches off the osmoreceptors.

5.2 RAAS (Renin-Angiotensin-Aldosterone System)

• Trigger: A fall in GFR/Blood pressure/Blood volume.
• Mechanism:
  1. JG Cells release an enzyme called Renin.
  2. Renin converts Angiotensinogen (from liver) into Angiotensin I.
  3. Angiotensin I is converted to Angiotensin II by ACE (Angiotensin Converting Enzyme).
  4. Angiotensin II is a powerful vasoconstrictor (increases BP) and stimulates the Adrenal Cortex to release Aldosterone.
  5. Aldosterone causes reabsorption of $Na^+$ and water from DCT.

5.3 ANF (Atrial Natriuretic Factor)

• Trigger: Increase in blood flow to the atria of the heart.
• Action: Causes vasodilation and inhibits the RAAS. It acts as a check and balance to the RAAS.

6. Micturition and Other Organs

Micturition: The process of release of urine.

• The stretch receptors on the wall of the urinary bladder send signals to the CNS.
• The CNS passes on motor messages to initiate contraction of smooth muscles of the bladder and simultaneous relaxation of the urethral sphincter.

Other Excretory Organs:

• Lungs: Remove $CO_2$ (18L/day) and water.
• Liver: Secretes bilirubin, biliverdin, cholesterol, and vitamins into bile, which eventually leaves with digestive waste.
• Skin: Sweat (contains $NaCl$, urea, lactic acid) for cooling; Sebaceous glands eliminate sterols, hydrocarbons, and waxes through sebum.

7. Disorders of the Excretory System

1. Uremia: Accumulation of urea in blood due to kidney malfunction. Extremely toxic; can lead to kidney failure.
2. Renal Calculi (Kidney Stones): Stone or insoluble mass of crystallized salts (usually Oxalates) formed within the kidney.
3. Glomerulonephritis: Inflammation of the glomeruli, often caused by an immune response or infection.
4. Renal Failure: The inability of kidneys to filter waste. Managed via Hemodialysis or Kidney Transplantation.

Hemodialysis Procedure:

• Blood is drained from a convenient artery and mixed with an anticoagulant like heparin.
• It is passed through a dialyzing unit containing a coiled cellophane tube surrounded by dialyzing fluid.
• The fluid has the same composition as plasma except the nitrogenous wastes.
• Wastes diffuse out of the blood into the fluid.
• Purified blood is pumped back via a vein after adding anti-heparin.

8. Solved MCQs (NEET Pattern)

Q1. A person who is on a long hunger strike and is surviving only on water, will have: A. Less urea in his urine
B. More sodium in his urine
C. Less amino acids in his urine
D. More glucose in his blood
Answer: A.
Explanation: Urea is a byproduct of protein metabolism. During starvation, once the protein stores are depleted or not being replenished, the production of urea decreases.

Q2. Which of the following does not favor the formation of large quantities of dilute urine? A. Alcohol
B. Caffeine
C. Renin
D. Atrial Natriuretic Factor
Answer: C.
Explanation: Renin initiates the RAAS, which leads to the reabsorption of water and $Na^+$, resulting in concentrated urine. Alcohol and Caffeine inhibit ADH, leading to diuresis (dilute urine).

Q3. If the GFR is $125 \text{ ml/min}$ and the distal convoluted tubule reabsorption is inhibited, the immediate effect will be: A. Increase in urine volume
B. Decrease in blood pressure
C. Increase in GHP
D. No change in urine output
Answer: A.
Explanation: DCT is responsible for conditional reabsorption. If inhibited, the water that should have been reabsorbed stays in the tubule, increasing volume.

Q4. The part of the nephron that is impermeable to water is: A. Proximal Convoluted Tubule
B. Descending limb of Loop of Henle
C. Ascending limb of Loop of Henle
D. Collecting duct
Answer: C.
Explanation: The ascending limb allows transport of electrolytes but is impermeable to water, which helps in diluting the filtrate as it moves upward.

Q5. A decrease in blood pressure/volume will not cause the release of: A. Renin
B. Atrial Natriuretic Factor
C. Aldosterone
D. ADH
Answer: B.
Explanation: ANF is released in response to increased blood pressure to lower it.

Q6. What is the osmolarity of the filtrate at the bend of the Loop of Henle? A. 300 mOsm/L
B. 600 mOsm/L
C. 900 mOsm/L
D. 1200 mOsm/L
Answer: D.
Explanation: As the filtrate moves down the descending limb, water is lost to the interstitium, reaching maximum concentration at the bottom (1200 mOsm/L).

Q7. Human kidneys can produce urine nearly _______ times concentrated than the initial filtrate formed. A. 2
B. 4
C. 10
D. 100
Answer: B.
Explanation: Initial filtrate is 300 mOsm/L; final urine can be 1200 mOsm/L ($300 \times 4 = 1200$).

Q8. The "Columns of Bertin" in the kidney of mammals are formed as extensions of: A. Medulla into cortex
B. Cortex into medulla
C. Pelvis into ureter
D. Medulla into pelvis
Answer: B.
Explanation: The cortex extends between the medullary pyramids as renal columns called Columns of Bertin.

9. Diagram-Based Logic Questions

Figure Logic: The Malpighian Body

• If the diameter of the Afferent Arteriole is narrowed and the Efferent Arteriole is widened, what happens to GFR?
• Analysis: GFR depends on hydrostatic pressure. The Afferent arteriole is normally wider than the Efferent, creating a "bottleneck" pressure. If you reverse this, the pressure drops, and filtration ceases.

Figure Logic: Counter-current Exchange

• Identify the movement of Urea. Where does it leave the tubule and where does it re-enter?
• Analysis: Urea leaves the Collecting Duct (bottom part) and enters the Thin Ascending Limb of the Loop of Henle to maintain medullary osmolarity. This is "Urea Recycling."

Locomotion & Movement

Movement is one of the significant features of living beings. Animals and plants exhibit a wide range of movements. While movement refers to the change in posture or position of any part of the body, locomotion specifically refers to voluntary movements that result in a change of location. In humans, this requires the coordinated activity of the muscular, skeletal, and neural systems.

1. Types of Movement

Cells of the human body exhibit three main types of movement:

A. Amoeboid Movement

This movement is effected by pseudopodia formed by the streaming of protoplasm (as in Amoeba). In the human body, specialized cells like macrophages and leucocytes (WBCs) in the blood exhibit amoeboid movement to move through tissue spaces (diapedesis). Cytoskeletal elements like microfilaments are also involved.

B. Ciliary Movement

Occurs in internal tubular organs lined by ciliated epithelium.

• Trachea: Cilia help in removing dust particles and foreign substances inhaled with atmospheric air.
• Oviducts (Fallopian tubes): Passage of ova through the female reproductive tract is facilitated by ciliary movement.

C. Muscular Movement

Movement of our limbs, jaws, tongue, etc., requires muscular movement. The contractile property of muscles is effectively used for locomotion and other movements. Locomotion requires a perfect coordinated activity of muscular, skeletal, and neural systems.

2. Detailed Structure of Skeletal Muscle

Skeletal muscle is composed of many muscle bundles or fascicles held together by a common collagenous connective tissue layer called fascia. Each fascicle contains a number of muscle fibres.

The Muscle Fibre (Cell)

• Sarcolemma: The plasma membrane lining the muscle fibre.
• Sarcoplasm: The cytoplasm, containing multiple nuclei (syncytium).
• Sarcoplasmic Reticulum (SR): The endoplasmic reticulum of the muscle fibre, which serves as a storehouse of calcium ions ($Ca^{2+}$).
• Myofibrils: Parallelly arranged filaments in the sarcoplasm. These exhibit alternate dark and light bands.

The Myofilaments: Actin and Myosin

The striated appearance is due to the distribution pattern of two important proteins:

1. Actin (Light band): Also called the I-band (Isotropic band).
2. Myosin (Dark band): Also called the A-band (Anisotropic band).

The Sarcomere: The Functional Unit

The myofibril is divided into functional units called sarcomeres.

• Z-line: A sharp dark line that bisects each I-band. The portion of a myofibril between two successive Z-lines is called a sarcomere.
• M-line: A thin fibrous membrane in the middle of the A-band that holds thick filaments together.
• H-zone: The central part of the thick filament (A-band) that is NOT overlapped by thin filaments during the resting state.

Summary of Sarcomere Geography: $$ \text{Sarcomere} = \frac{1}{2} \text{I-band} + \text{Full A-band} + \frac{1}{2} \text{I-band} $$ $$\text{Width of A-band} = \text{Constant during contraction}$$

3. Contractile Proteins: Molecular Anatomy

Thick Filament (Myosin)

Each myosin filament is a polymer of many monomeric proteins called Meromyosins.

• Heavy Meromyosin (HMM): The globular head and short arm. It projects outwards at regular distance and angle from the surface of a polymerized myosin filament and is known as the cross arm.
• Light Meromyosin (LMM): The tail portion.
• The globular head contains an Active ATPase enzyme and has binding sites for ATP and active sites for actin.

Thin Filament (Actin)

Each actin (F-actin) filament is a polymer of monomeric G-actin (Globular actin).

• Tropomyosin: Two filaments of another protein, tropomyosin, run close to the ‘F’ actins throughout its length.
• Troponin: A complex protein distributed at regular intervals on the tropomyosin. In the resting state, a subunit of troponin masks the active binding sites for myosin on the actin filaments.

4. Mechanism of Muscle Contraction: Sliding Filament Theory

The mechanism of muscle contraction is best explained by the Sliding Filament Theory, which states that contraction of a muscle fibre takes place by the sliding of the thin filaments over the thick filaments.

Step-by-Step Process:

1. Excitation: A neural signal reaching the neuromuscular junction releases Acetylcholine (ACh), which generates an action potential in the sarcolemma.
2. Calcium Release: This spreads through the muscle fibre and causes the release of Calcium ions ($Ca^{2+}$) from the Sarcoplasmic Reticulum into the sarcoplasm.
3. Unmasking: $Ca^{2+}$ binds with the troponin subunit on actin filaments, thereby removing the masking of active sites for myosin.
4. Cross-Bridge Formation: Utilizing the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross-bridge.
5. Power Stroke (Sliding): This pulls the attached actin filaments towards the centre of the 'A' band. The Z-line attached to these actins is also pulled inwards, thereby causing a shortening of the sarcomere (contraction).
6. Relaxation: Myosin releases the ADP and $P_i$ and goes back to its relaxed state. A new ATP binds and the cross-bridge is broken. The $Ca^{2+}$ ions are pumped back to the sarcoplasmic cisternae, resulting in the masking of actin filaments.

Changes during Contraction:

• Sarcomere length: Decreases.
• I-band length: Decreases.
• H-zone length: Decreases (may disappear).
• A-band length: Remains constant.

5. Red vs. White Muscle Fibres

Muscles contain a red colored oxygen-storing pigment called Myoglobin. Based on the amount of myoglobin and mitochondria, fibres are classified:

6. The Human Skeletal System

The skeletal system consists of 206 bones and a few cartilages. It is divided into two main groups:

A. Axial Skeleton (80 Bones)

Distributed along the main axis of the body.

1. Skull (29):
   • Cranial bones: 8
   • Facial bones: 14
   • Hyoid: 1 (U-shaped bone at the base of buccal cavity)
   • Ear Ossicles: 6 (Malleus, Incus, Stapes $\times$ 2)
2. Vertebral Column (26):
   • Cervical: 7 (C1 is Atlas, C2 is Axis)
   • Thoracic: 12
   • Lumbar: 5
   • Sacral: 1 (Fused from 5)
   • Coccygeal: 1 (Fused from 4)
3. Sternum (1): Flat bone on the ventral midline of thorax.
4. Ribs (24): 12 pairs.
   • True ribs: 1st - 7th pairs (attached to sternum).
   • Vertebrochondral (False) ribs: 8th, 9th, 10th pairs.
   • Floating ribs: 11th and 12th pairs (not connected ventrally).

B. Appendicular Skeleton (126 Bones)

Consists of the bones of the limbs along with their girdles.

1. Forelimbs (Hand) (30 $\times$ 2 = 60): Humerus, Radius, Ulna, Carpals (8), Metacarpals (5), Phalanges (14).
2. Hindlimbs (Leg) (30 $\times$ 2 = 60): Femur (longest bone), Tibia, Fibula, Tarsals (7), Metatarsals (5), Phalanges (14), Patella (knee cap).
3. Pectoral Girdle (4): Clavicle (2) and Scapula (2).
4. Pelvic Girdle (2): Two coxal bones. Each coxal bone is formed by the fusion of three bones: Ilium, Ischium, and Pubis.

7. Types of Joints

Joints are points of contact between bones, or between bones and cartilages.

1. Fibrous Joints: Allow no movement. Flat skull bones which fuse end-to-end with the help of dense fibrous connective tissues in the form of sutures.
2. Cartilaginous Joints: Bones are joined together with the help of cartilages. Permits limited movement. e.g., between adjacent vertebrae in the vertebral column.
3. Synovial Joints: Characterized by the presence of a fluid-filled synovial cavity between the articulating surfaces of the two bones. Allows considerable movement.
   • Ball and Socket joint: Between humerus and pectoral girdle.
   • Hinge joint: Knee joint, Elbow joint.
   • Pivot joint: Between Atlas and Axis.
   • Gliding joint: Between the carpals.
   • Saddle joint: Between carpal and metacarpal of thumb.

8. Disorders of the Muscular and Skeletal System

• Myasthenia Gravis: Auto-immune disorder affecting neuromuscular junction leading to fatigue, weakening, and paralysis of skeletal muscle.
• Muscular Dystrophy: Progressive degeneration of skeletal muscle mostly due to genetic disorder (e.g., Duchenne Muscular Dystrophy).
• Tetany: Rapid spasms (wild contractions) in muscle due to low $Ca^{2+}$ in body fluid (Hypocalcemia).
• Arthritis: Inflammation of joints.
• Osteoporosis: Age-related disorder characterized by decreased bone mass and increased chances of fractures. Decreased level of estrogen is a common cause in elderly women.
• Gout: Inflammation of joints due to accumulation of uric acid crystals.

Worked Examples & MCQs

Example 1: Calculating the total count of Phalanges. Solution: Each limb (hand or foot) has 14 phalanges. The formula is 2, 3, 3, 3, 3 (Thumb/Big toe has 2, others have 3). Total Phalanges = $14 (\text{left hand}) + 14 (\text{right hand}) + 14 (\text{left foot}) + 14 (\text{right foot}) = 56$ bones.

Example 2: Identification of the "Floating Ribs". Concept: Floating ribs are the 11th and 12th pairs. They are called floating because they are attached dorsally to the vertebrae but have no ventral attachment to the sternum or other ribs.

8 Solved MCQs for NEET

Q1. The H-zone in the skeletal muscle fibre is due to: A. The central gap between actin filaments extending through myosin filaments in the A-band. B. Extension of myosin filaments in the central portion of the A-band. C. The absence of myofibrils in the central portion of A-band. D. The central gap between myosin filaments in the A-band. Answer: A.

Q2. Which of the following is an autoimmune disorder? A. Muscular dystrophy B. Myasthenia gravis C. Tetany D. Gout Answer: B.

Q3. Name the ion responsible for unmasking of active sites for myosin for cross-bridge activity during muscle contraction. A. Calcium B. Magnesium C. Sodium D. Potassium Answer: A.

Q4. Lack of relaxation between successive stimuli in sustained muscle contraction is known as: A. Fatigue B. Tetanus C. Tonus D. Spasm Answer: B.

Q5. The pivot joint between atlas and axis is a type of: A. Cartilaginous joint B. Synovial joint C. Saddle joint D. Fibrous joint Answer: B.

Q6. Which of the following is NOT a function of the skeletal system? A. Production of erythrocytes B. Storage of minerals C. Production of body heat D. Locomotion Answer: C (Note: Heat production is a function of Muscular system/metabolism, though related).

Q7. Osteoporosis, an age-related disease of skeletal system, may occur due to: A. Immune disorder affecting neuromuscular junction B. High concentration of $Ca^{2+}$ and $Na^{+}$ C. Decreased level of estrogen D. Accumulation of uric acid leading to inflammation of joints. Answer: C.

Q8. During muscle contraction, which of the following events occur? (i) H-zone disappears (ii) A-band widens (iii) I-band reduces in width (iv) Width of A-band is unaffected (v) M-line and Z-line come closer A. (i), (iii), (iv), (v) B. (i), (ii), (v) C. (ii), (iv), (v) D. (i), (ii), (iii) Answer: A. (A-band width never changes).

Mnemonic for Carpals (8 Bones): "She Looks Too Pretty, Try To Catch Her" Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate.

Neural Control & Coordination

Human survival depends on the ability to detect changes in the external and internal environment and respond to them in a synchronized manner. This coordination is achieved through two major systems: the Nervous System (fast, point-to-point electrical signaling) and the Endocrine System (slow, chemical signaling). Neural coordination is the process through which two or more organs interact and complement the functions of one another.

1. The Division of the Human Nervous System

The human nervous system is structurally and functionally divided to manage complex inputs and motor outputs.

2. The Neuron: Structural & Functional Unit

A neuron consists of three major parts: the cell body (cyton), dendrites, and the axon.

A. Structural Components

1. Cell Body: Contains the nucleus, cytoplasm, and granular bodies called Nissl’s granules (sites of protein synthesis).
2. Dendrites: Short, branched fibers that project out of the cell body. They contain Nissl’s granules and receive incoming signals.
3. Axon: A long fiber that transmits impulses away from the cell body. The distal end is branched into synaptic knobs, which contain synaptic vesicles filled with neurotransmitters.

B. Types of Neurons

• Multipolar: One axon and two or more dendrites (Found in the Cerebral Cortex).
• Bipolar: One axon and one dendrite (Found in the Retina of the eye).
• Unipolar: Cell body with one axon only (Found usually in the embryonic stage).

C. Myelinated vs. Non-myelinated

• Myelinated: Enveloped by Schwann cells, which form a myelin sheath. Gaps between adjacent myelin sheaths are called Nodes of Ranvier. Found in spinal and cranial nerves.
• Non-myelinated: Schwann cells are present but do not form a sheath. Found in Autonomous and Somatic neural systems.

3. Nerve Impulse Conduction: The Ionic Basis

Neurons are "excitable cells" because their membranes exist in a polarized state.

Phase I: Resting Membrane Potential (RMP)

When a neuron is not conducting an impulse:

1. The axonal membrane is more permeable to $K^+$ and nearly impermeable to $Na^+$.
2. The membrane is also impermeable to negatively charged proteins in the axoplasm.
3. Ionic Concentration: The axoplasm has high $K^+$ and low $Na^+$, while the extracellular fluid (ECF) has high $Na^+$ and low $K^+$.
4. Active Transport: The Na/K Pump moves $3 Na^+$ out for every $2 K^+$ moved in, using ATP.
5. Result: The outer surface is positively charged, and the inner surface is negatively charged. The potential difference is approximately $-70 mV$.

Phase II: Depolarization (Action Potential)

1. When a stimulus is applied at site A, the membrane becomes freely permeable to $Na^+$.
2. $Na^+$ rushes into the cell (influx).
3. The polarity is reversed: the inner side becomes positive, and the outer side becomes negative.
4. This electrical potential difference is the Action Potential (approximately $+30$ to $+40 mV$).

Phase III: Repolarization

1. The rise in $Na^+$ permeability is extremely short-lived.
2. Immediately, $K^+$ permeability increases.
3. $K^+$ diffuses outside the membrane (efflux), restoring the resting potential of the membrane.

Mathematical Note: The Nernst Equation helps determine the equilibrium potential for a specific ion: $$E_{ion} = \frac{RT}{zF} \ln \frac{[ion]{out}}{[ion]{in}}$$ For $K^+$, the equilibrium potential is near $-90 mV$, while for $Na^+$, it is $+60 mV$. The resting potential of $-70 mV$ is closer to $K^+$ because the membrane is more "leaky" to potassium.

4. Synaptic Transmission

The junction between two neurons is called a Synapse.

A. Electrical Synapse

• Membranes of pre- and post-synaptic neurons are in very close proximity.
• Current flows directly from one neuron to another.
• Faster than chemical synapses but rare in humans.

B. Chemical Synapse

• Separated by a fluid-filled space called the synaptic cleft.
• Requires Neurotransmitters (e.g., Acetylcholine, Dopamine).

Steps of Transmission:

1. Action potential reaches the axon terminal.
2. Voltage-gated $Ca^{2+}$ channels open; $Ca^{2+}$ enters the terminal.
3. Synaptic vesicles fuse with the plasma membrane and release neurotransmitters into the cleft (Exocytosis).
4. Neurotransmitters bind to specific receptors on the post-synaptic membrane.
5. This opening of ion channels generates a new potential:
   • EPSP (Excitatory Post-Synaptic Potential): If $Na^+$ channels open (Depolarization).
   • IPSP (Inhibitory Post-Synaptic Potential): If $Cl^-$ or $K^+$ channels open (Hyperpolarization).

5. The Human Brain

The brain is protected by the skull and three layers of cranial meninges:

1. Dura mater (Outer, tough)
2. Arachnoid mater (Middle, thin)
3. Pia mater (Inner, vascular, in contact with brain tissue)

A. Forebrain (Prosencephalon)

• Cerebrum: Divided into two halves by the corpus callosum (a tract of nerve fibers). The outer layer is the Cerebral Cortex (Grey matter, due to cell bodies). It contains:
  • Motor areas: Control voluntary movements.
  • Sensory areas: Receive sensory input.
  • Association areas: Responsible for complex functions like intersensory associations, memory, and communication.
• Thalamus: The major coordinating center for sensory and motor signaling.
• Hypothalamus: Located at the base of the thalamus.
  • Controls body temperature, urge for eating and drinking.
  • Secretes hypothalamic hormones.
  • Interacts with the Limbic System (Amygdala + Hippocampus) to regulate sexual behavior and emotions (excitement, pleasure, fear).

B. Midbrain (Mesencephalon)

• Located between the thalamus/hypothalamus and the Pons.
• A canal called the Cerebral Aqueduct passes through it.
• The dorsal portion consists of four round lobes called the Corpora Quadrigemina (involved in visual and auditory reflexes).

C. Hindbrain (Rhombencephalon)

• Pons: Consists of fiber tracts that interconnect different regions of the brain.
• Cerebellum: Has a very convoluted surface to provide additional space for many more neurons. Controls balance, posture, and coordination.
• Medulla Oblongata: Connects to the spinal cord. Contains centers that control respiration, cardiovascular reflexes, and gastric secretions.

Note: The Brain Stem includes the Midbrain, Pons, and Medulla Oblongata.

6. The Reflex Arc

A reflex action is an involuntary, instantaneous response to a stimulus.

• Afferent Neuron: Receives signal from a sensory organ and transmits it via the dorsal nerve root into the CNS.
• Efferent Neuron: Carries signals from the CNS via the ventral root to the effector (muscle/gland).
• Monosynaptic Reflex: Only two neurons (Sensory and Motor); e.g., Knee-jerk reflex.
• Polysynaptic Reflex: Involves interneurons between sensory and motor neurons; e.g., Withdrawing hand from a hot object.

7. Sensory Reception and Processing: The Eye

The eye is located in the orbit of the skull.

Anatomy of the Eyeball

1. Outer Layer: Sclera (dense connective tissue). The anterior transparent portion is the Cornea.
2. Middle Layer: Choroid (bluish, vascular). Anteriorly, it thickens to form the Ciliary Body, which continues to form the Iris (the colored part of the eye).
3. Inner Layer: Retina.
   • Contains three layers of cells (from inside to outside): Ganglion cells, Bipolar cells, Photoreceptor cells.
   • Two types of Photoreceptors: Rods (scotopic/twilight vision; contain Rhodopsin) and Cones (photopic/daylight and color vision).

Important Landmarks

• Blind Spot: Where the optic nerve leaves the eye; no photoreceptors are present.
• Macula Lutea: A yellowish spot lateral to the blind spot with a central pit called the Fovea. The fovea contains only densely packed cones and is the point of highest visual acuity.
• Aqueous Chamber: Space between cornea and lens (contains watery aqueous humor).
• Vitreous Chamber: Space between lens and retina (contains transparent vitreous humor).

Mechanism of Vision

Light $\rightarrow$ Cornea $\rightarrow$ Lens $\rightarrow$ Retina $\rightarrow$ Dissociation of Retinal from Opsin (in Rhodopsin) $\rightarrow$ Change in membrane permeability $\rightarrow$ Potential generated in photoreceptors $\rightarrow$ Bipolar cells $\rightarrow$ Ganglion cells $\rightarrow$ Optic Nerve $\rightarrow$ Visual Cortex (Brain).

8. Sensory Reception and Processing: The Ear

The ear performs two functions: Hearing and Maintenance of body balance.

Anatomy

1. Outer Ear: Pinna and External Auditory Meatus. The meatus leads to the Tympanic Membrane (eardrum).
2. Middle Ear: Contains three ossicles—Malleus, Incus, and Stapes (attached to the oval window). The Eustachian tube connects the middle ear to the pharynx (equalizes pressure).
3. Inner Ear (Labyrinth):
   • Bony Labyrinth: A series of channels filled with perilymph.
   • Membranous Labyrinth: Inside the bony labyrinth, filled with endolymph.
   • Cochlea: The coiled portion of the labyrinth. Contains the Organ of Corti on the Basilar membrane, which has hair cells (auditory receptors).
   • Vestibular Apparatus: Located above the cochlea. Comprises three Semi-circular canals (balance during rotation) and the Saccule/Utricle (linear acceleration). The base of the canals is the Ampulla, containing the Crista. The Saccule/Utricle contain the Macula.

Mechanism of Hearing

Sound waves $\rightarrow$ Ear drum $\rightarrow$ Ossicles $\rightarrow$ Oval window $\rightarrow$ Fluid of Cochlea $\rightarrow$ Ripples in Basilar membrane $\rightarrow$ Hair cells bend against Tectorial membrane $\rightarrow$ Nerve impulses $\rightarrow$ Auditory Nerve $\rightarrow$ Auditory Cortex.

9. Solved MCQs (NEET Pattern)

Q1. The resting membrane potential of a neuron is maintained by: A) Purely passive diffusion of $Na^+$ B) The Sodium-Potassium pump moving $2 Na^+$ out and $3 K^+$ in C) The Sodium-Potassium pump moving $3 Na^+$ out and $2 K^+$ in D) Voltage-gated Calcium channels Answer: C. The Na/K ATPase pump actively maintains the gradient by moving 3 Sodium ions out for every 2 Potassium ions brought in using ATP.

Q2. Which part of the brain is responsible for thermoregulation? A) Cerebrum B) Hypothalamus C) Corpus Callosum D) Medulla Oblongata Answer: B. The hypothalamus contains centers for body temperature, hunger, and thirst.

Q3. In the human eye, the point of maximum visual acuity is the: A) Blind spot B) Sclera C) Fovea D) Optic disc Answer: C. The fovea is a thinned-out portion of the retina where only cones are densely packed.

Q4. Matching Question:

1. Malleus - (i) Coiled part of labyrinth
2. Cochlea - (ii) Hammer-shaped ossicle
3. Pons - (iii) Connects cerebral hemispheres
4. Corpus Callosum - (iv) Brain stem component Answer: 1-(ii), 2-(i), 3-(iv), 4-(iii).

Q5. Identify the correct sequence of impulse transmission across a chemical synapse:

1. Binding to receptors
2. Influx of $Ca^{2+}$
3. Release of neurotransmitter
4. Action potential reaches terminal A) 4-2-3-1 B) 2-4-3-1 C) 4-3-2-1 D) 1-2-3-4 Answer: A. The arrival of the AP triggers $Ca^{2+}$ entry, which causes vesicle fusion and neurotransmitter release, followed by receptor binding.

Q6. Diagram-based: In a diagram of the reflex arc, the cell body of the sensory neuron is located in the: A) Ventral horn B) Dorsal root ganglion C) Grey matter of spinal cord D) Effector organ Answer: B. The afferent (sensory) neuron has its cell body in the dorsal root ganglion.

Q7. The "white matter" of the brain appears white because of: A) High density of cell bodies B) Absence of blood vessels C) Myelin sheaths of axons D) Presence of Nissl's granules Answer: C. The myelin sheath is composed of lipids, which provide a white, glistening appearance to the nerve tracts.

Q8. Which part of the ear is strictly responsible for dynamic balance (rotational movement)? A) Organ of Corti B) Macula C) Crista Ampullaris D) Eustachian tube Answer: C. The Crista (found in the ampulla of semi-circular canals) manages rotational balance, while the Macula manages linear balance.

Q9. During repolarization of a neuron: A) $Na^+$ channels open B) $K^+$ channels open C) Both $Na^+$ and $K^+$ channels close D) $Cl^-$ moves out Answer: B. Repolarization occurs due to the efflux of $K^+$ ions following the closure of $Na^+$ channels.

Q10. The function of the Eustachian tube is to: A) Amplify sound waves B) Protect the inner ear from loud noises C) Equalize air pressure on either side of the eardrum D) Transmit vibrations to the oval window Answer: C. It connects the middle ear to the pharynx to ensure the tympanic membrane is not damaged by pressure changes.

Chemical Coordination & Integration

In complex multicellular organisms like humans, the nervous system provides a point-to-point rapid coordination. however, nerve fibres do not innervate all cells of the body and cellular functions need to be continuously regulated. This necessitates a special kind of coordination and integration provided by hormones. The Endocrine System and the Nervous System jointly coordinate and integrate all physiological activities in the body.

1. The Nature of Hormones

Endocrine glands are ductless glands. Their secretions are called hormones.

• Classical Definition: A chemical produced by endocrine glands and released into the blood and transported to a distantly located target organ.
• Modern Scientific Definition: Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts.

2. The Hypothalamus-Pituitary Axis

The Hypothalamus is the basal part of the diencephalon (forebrain) and it regulates a wide spectrum of body functions. It contains several groups of neurosecretory cells called nuclei which produce hormones.

A. Hypothalamic Hormones

These hormones reach the pituitary gland through a portal circulatory system and regulate the functions of the anterior pituitary.

1. Releasing Hormones: e.g., Gonadotrophin Releasing Hormone (GnRH) stimulates the pituitary synthesis and release of gonadotrophins.
2. Inhibiting Hormones: e.g., Somatostatin from the hypothalamus inhibits the release of growth hormone from the pituitary.

B. The Pituitary Gland (Hypophysis)

Located in a bony cavity called Sella tursica and is attached to the hypothalamus by a stalk. It is divided anatomically into an Adenohypophysis and a Neurohypophysis.

Note: In humans, the pars intermedia is almost merged with pars distalis. The neurohypophysis does not synthesize hormones; it stores and releases hormones actually synthesized by the hypothalamus.

3. Master Table: Endocrine Glands, Hormones, and Functions

This table summarizes the core curriculum for NEET regarding hormone actions and associated clinical disorders.

4. Detailed Organ Analysis

A. Thyroid Gland

The thyroid gland is composed of two lobes located on either side of the trachea, interconnected by a thin flap of connective tissue called the isthmus. It is composed of follicles and stromal tissues.

• Iodine Necessity: Iodine is essential for the normal rate of hormone synthesis in the thyroid.
• Hypothyroidism: During pregnancy, this causes Cretinism (stunted growth, mental retardation, low I.Q., abnormal skin). In adult women, it may cause irregular menstrual cycles. Simple Goitre is the enlargement of the gland due to iodine deficiency.
• Hyperthyroidism: Due to cancer of the thyroid gland or nodules. Exophthalmic goitre (Graves' disease) is characterized by protrusion of eyeballs, increased BMR, and weight loss.

B. Parathyroid Gland

Four parathyroid glands are present on the back side of the thyroid gland.

• PTH (Parathyroid Hormone): A peptide hormone. It is hypercalcemic (increases blood $Ca^{2+}$ levels).
• Action: Stimulates bone resorption (demineralization), reabsorption of $Ca^{2+}$ by renal tubules, and increases $Ca^{2+}$ absorption from digested food.
• Calcium Homeostasis: Maintained by the antagonistic actions of TCT (lowers $Ca^{2+}$) and PTH (raises $Ca^{2+}$).

C. Adrenal Gland

Located at the anterior part of each kidney. It consists of two types of tissues:

1. Adrenal Medulla: Secretes Catecholamines (Adrenaline/Epinephrine and Noradrenaline/Norepinephrine). These increase alertness, pupillary dilation, piloerection (raising of hairs), sweating, heart rate, and breakdown of glycogen/lipids.
2. Adrenal Cortex: Divided into three layers (Mnemonic: GFR - outside to inside):
   • G - Zona Glomerulosa (Secretes Mineralocorticoids like Aldosterone).
   • F - Zona Fasciculata (Secretes Glucocorticoids like Cortisol).
   • R - Zona Reticularis (Secretes Androgenic steroids).

D. Pancreas

A composite (Heterocrine) gland. The endocrine part consists of Islets of Langerhans ($\approx 1$ to 2 million).

• $\alpha$-cells: Secrete Glucagon. It acts on hepatocytes and stimulates glycogenolysis and gluconeogenesis, leading to hyperglycemia.
• $\beta$-cells: Secrete Insulin. It enhances cellular glucose uptake and utilization. It stimulates glycogenesis (glucose $\rightarrow$ glycogen).
• $\delta$-cells: Secrete Somatostatin which inhibits both insulin and glucagon.

E. Thymus and Pineal

• Thymus: Located between lungs behind the sternum. It plays a major role in the differentiation of T-lymphocytes (Cell-mediated immunity) and promotes antibody production (Humoral immunity). It degenerates in old individuals.
• Pineal: Located on the dorsal side of the forebrain. Melatonin influences metabolism, pigmentation, the menstrual cycle, and our defense capability.

5. Non-Endocrine Hormones (Glands not specialized)

Hormones are also secreted by tissues which are not organized endocrine glands:

1. Heart: The atrial wall secretes Atrial Natriuretic Factor (ANF). It causes vasodilation and decreases blood pressure (Antagonistic to RAAS).
2. Kidney: Juxtaglomerular (JG) cells produce Erythropoietin (EPO), which stimulates erythropoiesis (RBC formation).
3. Gastro-intestinal Tract:
   • Gastrin: Acts on gastric glands, stimulates secretion of $HCl$ and pepsinogen.
   • Secretin: Acts on exocrine pancreas, stimulates secretion of water and bicarbonate ions.
   • CCK (Cholecystokinin): Acts on pancreas and gallbladder, stimulates secretion of pancreatic enzymes and bile juice.
   • GIP (Gastric Inhibitory Peptide): Inhibits gastric secretion and motility.

6. Mechanism of Hormone Action

Hormones produce their effects by binding to specific proteins called Hormone Receptors located in the target tissues.

Classification by Chemical Nature

1. Peptide, Polypeptide, Protein Hormones: Insulin, Glucagon, Pituitary hormones, Hypothalamic hormones.
2. Steroids: Cortisol, Testosterone, Estradiol, Progesterone.
3. Iodothyronines: Thyroid hormones.
4. Amino-acid derivatives: Epinephrine.

Two Main Mechanisms

Method A: Membrane-bound Receptors (Protein Hormones) Proteins cannot enter the target cell.

1. Hormone (First messenger) binds to a surface receptor.
2. Formation of Hormone-Receptor Complex.
3. Generation of Second Messengers (e.g., $cAMP$, $IP_3$, $Ca^{2+}$).
4. Biochemical responses leading to physiological responses (e.g., Ovarian growth).

Method B: Intracellular Receptors (Steroid and Thyroid Hormones) Lipid-soluble hormones enter the cell.

1. Hormone enters the cytoplasm and binds to a receptor (usually in the nucleus).
2. Hormone-Receptor complex interacts with the Genome (DNA).
3. Stimulation of $mRNA$ synthesis and translation (Protein synthesis).
4. Tissue growth and differentiation.

7. Worked Example: The Calcium Balance Logic

Problem: How does the body respond to a sudden drop in blood calcium levels?

Step-by-Step Physiological Pathway:

1. Detection: Low $Ca^{2+}$ levels in blood are detected by the Parathyroid glands.
2. Secretion: The glands release PTH (Parathyroid Hormone).
3. Action 1 (Bone): PTH stimulates Osteoclasts to break down bone matrix (resorption), releasing $Ca^{2+}$ into the blood.
4. Action 2 (Kidney): PTH increases $Ca^{2+}$ reabsorption in the DCT and collecting ducts.
5. Action 3 (Intestine): PTH activates Vitamin D, which increases absorption of $Ca^{2+}$ from the diet.
6. Result: Blood $Ca^{2+}$ levels return to normal (Homeostasis).

8. Solved MCQs for NEET

Q1. Which of the following is an amino acid derivative hormone? A. Epinephrine B. Insulin C. Estradiol D. Testosterone Answer: A. Epinephrine is derived from the amino acid Tyrosine.

Q2. The "3F" glands (Flight, Fight, Fright) refers to: A. Thyroid B. Adrenal Medulla C. Pancreas D. Thymus Answer: B. Adrenal Medulla secretes emergency hormones.

Q3. GnRH, a hypothalamic hormone, needed in reproduction, acts on: A. Anterior pituitary gland and stimulates secretion of LH and FSH. B. Posterior pituitary gland and stimulates secretion of oxytocin and FSH. C. Posterior pituitary gland and stimulates secretion of LH and relaxin. D. Anterior pituitary gland and stimulates secretion of LH and oxytocin. Answer: A. Hypothalamic hormones regulate the anterior pituitary.

Q4. A temporary endocrine gland in the human body is: A. Pineal gland B. Corpus luteum C. Corpus cardiacum D. Corpus allatum Answer: B. Corpus luteum is formed after ovulation and secretes progesterone.

Q5. Graves' disease is caused due to: A. Hyposecretion of thyroid gland B. Hypersecretion of thyroid gland C. Hyposecretion of adrenal gland D. Hypersecretion of adrenal gland Answer: B. It is a form of hyperthyroidism.

Q6. Which hormone is known as the "Emergency Hormone"? A. Thyroxine B. Adrenaline C. Insulin D. Glucagon Answer: B.

Q7. The hormone that stimulates the release of bicarbonate ions from the pancreas is: A. Gastrin B. Secretin C. CCK D. GIP Answer: B.

Q8. Hypercalcemic hormone is: A. TCT B. PTH C. Melatonin D. Aldosterone Answer: B. PTH increases blood calcium.

Q9. Which layer of the adrenal cortex is responsible for mineralocorticoids? A. Zona reticularis B. Zona fasciculata C. Zona glomerulosa D. Medulla Answer: C. Remember GFR ordering.

Q10. Which of the following uses $cAMP$ as a second messenger? A. Cortisol B. Testosterone C. Glucagon D. Thyroxine Answer: C. Glucagon is a peptide hormone and requires a second messenger. Steroid and thyroid hormones bind to intracellular receptors.

Summary Mnemonic for Layers of Adrenal Cortex:

• Go ——> Glomerulosa (Salt: Mineralocorticoids)
• Find ——> Fasciculata (Sugar: Glucocorticoids)
• Rita ——> Reticularis (Sex: Androgens)

30 Assertion-Reason & Statement-Based NEET Questions Solved

In the updated NEET (UG) pattern, Assertion-Reason (A-R) and Statement-I/Statement-II type questions constitute nearly 20-25% of the Biology section. These questions don't just test memory; they test your grasp of "Cause and Effect" and your ability to identify subtle nuances in NCERT phrasing.

Below are 30 high-yield questions covering the entirety of Human Physiology (Digestion to Locomotion and Neural Control), mapped to exact NCERT concepts.

Section 1: Digestion, Absorption, and Breathing

Q1. Assertion (A): The activities of the gastro-intestinal tract are under neural and hormonal control for proper coordination of different parts. Reason (R): Gastric and intestinal secretions are stimulated by neural signals.

• (a) Both A and R are true and R is the correct explanation of A.
• (b) Both A and R are true but R is NOT the correct explanation of A.
• (c) A is true but R is false.
• (d) A is false but R is true.

Answer: (b) Explanation: Both statements are correct according to NCERT. However, the Reason specifically mentions neural signals, which is only one part of the control mechanism. Hormonal control (via gastrin, CCK, etc.) is the other part. The Reason does not explain why coordination is necessary, it merely lists a component of the control.

Q2. Statement I: The presence of food in the oral cavity can stimulate the secretion of saliva. Statement II: Gastric and intestinal secretions are also stimulated by neural signals.

• (a) Statement I is correct but Statement II is incorrect.
• (b) Statement I is incorrect but Statement II is correct.
• (c) Both Statement I and Statement II are correct.
• (d) Both Statement I and Statement II are incorrect.

Answer: (c) NCERT Reference: Chapter 16 (Digestion and Absorption), Section 16.3. Neural and hormonal control.

Q3. Assertion (A): The maximum volume of air a person can breathe in after a forced expiration is called Vital Capacity (VC). Reason (R): Vital Capacity includes ERV, TV, and IRV.

• (a) Both A and R are true and R is the correct explanation of A.
• (b) Both A and R are true but R is NOT the correct explanation of A.
• (c) A is true but R is false.
• (d) A is false but R is true.

Answer: (a) Detailed Calculation: $$VC = ERV + TV + IRV$$ $$VC \approx 1100 + 500 + 2500 = 4100\text{ ml}$$ The Reason provides the anatomical components that define the capacity mentioned in the Assertion.

Q4. Statement I: Every 100 ml of oxygenated blood can deliver around 5 ml of $O_2$ to the tissues under normal physiological conditions. Statement II: Every 100 ml of deoxygenated blood delivers approximately 4 ml of $CO_2$ to the alveoli.

• (a) Both Statement I and Statement II are correct.
• (b) Statement I is correct but Statement II is incorrect.
• (c) Statement I is incorrect but Statement II is correct.
• (d) Both are incorrect.

Answer: (a) Explanation: These are direct numerical values from NCERT. Note the difference: 5ml for $O_2$ and 4ml for $CO_2$.

Section 2: Body Fluids and Circulation

Q5. Assertion (A): The SA node is called the pacemaker of the heart. Reason (R): SA node is responsible for initiating and maintaining the rhythmic contractile activity of the heart.

• (a) Both A and R are true and R explains A.
• (b) Both A and R are true but R does not explain A.
• (c) A is true, R is false.
• (d) A is false, R is true.

Answer: (a) Concept: The nodal tissue is auto-excitable. The SA node generates the maximum number of action potentials (70-75 $min^{-1}$).

Q6. Statement I: Person with ‘O’ blood group is called a universal donor. Statement II: The plasma of a person with ‘O’ blood group contains both anti-A and anti-B antibodies.

• (a) Both statements are true.
• (b) Both statements are false.
• (c) Statement I is true, Statement II is false.
• (d) Statement II is true, Statement I is false.

Answer: (a) Explanation: Person 'O' has no antigens (A or B) on RBCs, making them safe to donate. The presence of antibodies in their plasma is a separate fact, both are true.

Q7. Assertion (A): Heart failure is the same as cardiac arrest or a heart attack. Reason (R): Heart failure means the state of heart when it is not pumping blood effectively enough to meet the needs of the body.

• (a) Both A and R are true and R explains A.
• (b) Both A and R are true but R does not explain A.
• (c) A is false but R is true.
• (d) A is true but R is false.

Answer: (c) Mnemonic for Clinical Disorders:

Section 3: Excretory Products and Their Elimination

Q8. Statement I: An increase in blood flow to the atria of the heart can cause the release of Atrial Natriuretic Factor (ANF). Statement II: ANF causes vasoconstriction and thereby increases the blood pressure.

• (a) Statement I is correct, Statement II is incorrect.
• (b) Statement I is incorrect, Statement II is correct.
• (c) Both are correct.
• (d) Both are incorrect.

Answer: (a) Reasoning: ANF acts as a check on the RAAS mechanism. It causes vasodilation (not vasoconstriction) to decrease blood pressure.

Q9. Assertion (A): In the descending limb of the loop of Henle, the filtrate becomes hypertonic. Reason (R): The descending limb is permeable to water but almost impermeable to electrolytes.

• (a) Both A and R are true, R is correct explanation.
• (b) Both A and R are true, R is not correct explanation.
• (c) A is true, R is false.
• (d) A is false, R is true.

Answer: (a) Explanation: As water leaves the tubule into the medullary interstitium, the concentration of the remaining filtrate increases. Formula for Osmolarity change: $$C_1V_1 = C_2V_2$$ As Volume ($V$) decreases (water loss), Concentration ($C$) must increase.

Q10. Statement I: The Henle’s loop and vasa recta play a significant role in producing a concentrated urine. Statement II: The counter current mechanism helps to maintain a concentration gradient in the medullary interstitium.

• (a) Both statements are true.
• (b) Both statements are false.
• (c) Only statement I is true.
• (d) Only statement II is true.

Answer: (a) NCERT Fact: The gradient ranges from 300 mOsmol/L in the cortex to 1200 mOsmol/L in the inner medulla.

Section 4: Locomotion and Movement

Q11. Assertion (A): White muscle fibers depend on anaerobic process for energy. Reason (R): White muscle fibers have very less quantity of myoglobin and few mitochondria.

• (a) Both A and R are correct, R is the explanation.
• (b) Both A and R are correct, R is not the explanation.
• (c) A is true, R is false.
• (d) Both are false.

Answer: (a) Key Comparison Table:

Q12. Statement I: Myasthenia gravis is an autoimmune disorder affecting neuromuscular junctions. Statement II: It leads to progressivedegeneration of skeletal muscle mostly due to genetic disorder.

• (a) Statement I is correct, Statement II is incorrect.
• (b) Statement I is incorrect, Statement II is correct.
• (c) Both correct.
• (d) Both incorrect.

Answer: (a) Explanation: Statement II describes Muscular Dystrophy, which is genetic. Myasthenia gravis is autoimmune.

Q13. Assertion (A): The 8th, 9th and 10th pairs of ribs are called vertebrochondral ribs. Reason (R): They do not articulate directly with the sternum but join the seventh rib with the help of hyaline cartilage.

• (a) Both A and R are true, R explains A.
• (b) Both A and R are true, R doesn't explain A.
• (c) A is true, R is false.
• (d) A is false, R is true.

Answer: (a) Rib Classification:

1. True Ribs (1-7): Vertebrosternal.
2. False Ribs (8-10): Vertebrochondral.
3. Floating Ribs (11-12): Not connected ventrally.

Section 5: Neural Control and Coordination

Q14. Statement I: The electrical potential difference across the resting plasma membrane is called the resting potential. Statement II: The resting membrane is nearly impermeable to Potassium ions ($K^+$) and relatively permeable to Sodium ions ($Na^+$).

• (a) Statement I is correct, Statement II is incorrect.
• (b) Statement I is incorrect, Statement II is correct.
• (c) Both correct.
• (d) Both incorrect.

Answer: (a) Inversion Alert: At rest, the membrane is more permeable to $K^+$ and nearly impermeable to $Na^+$. This is a classic "trap" question where NCERT words are swapped.

Q15. Assertion (A): Visceral nervous system is a part of the peripheral nervous system. Reason (R): It comprises the whole complex of nerves, fibers, ganglia, and plexuses by which impulses travel from the CNS to the viscera and vice versa.

• (a) Both A and R are correct, R explains A.
• (b) Both are correct but R does not explain A.
• (c) A is true, R false.
• (d) A is false, R true.

Answer: (a) NCERT Section: 21.1. Human Neural System.

Q16. Statement I: Unmyelinated nerve fiber is enclosed by a Schwann cell. Statement II: Unmyelinated nerve fibers do not form a myelin sheath around the axon.

• (a) Both statements are correct.
• (b) Both are incorrect.
• (c) Statement I is true, II is false.
• (d) Statement I is false, II is true.

Answer: (a) Confusion Point: Most students think unmyelinated fibers lack Schwann cells. They do have Schwann cells; they just don't wrap tightly to form the sheath. Found in Autonomous and Somatic neural systems.

Section 6: Chemical Coordination and Integration

Q17. Assertion (A): T3 and T4 (Thyroid hormones) play an important role in the maintenance of the basal metabolic rate (BMR). Reason (R): Thyroid hormones support the process of red blood cell formation.

• (a) Both A and R are true but R is NOT the correct explanation of A.
• (b) Both A and R are true and R is the correct explanation of A.
• (c) A is true, R is false.
• (d) A is false, R is true.

Answer: (a) Explanation: Both statements are correct functions of Thyroid hormones (NCERT), but the increase in RBC formation does not explain the regulation of BMR. BMR regulation is linked to metabolic rate and heat production.

Q18. Statement I: Glucagon is a hypoglycemic hormone. Statement II: Insulin is a hyperglycemic hormone.

• (a) Both statements are true.
• (b) Both statements are false.
• (c) Statement I is true, II is false.
• (d) Statement I is false, II is true.

Answer: (b) Logic:

• Glucagon: Hyperglycemic (increases blood sugar).
• Insulin: Hypoglycemic (decreases blood sugar). Statements are exactly swapped.

Q19. Assertion (A): ADH (Antidiuretic hormone) helps in water reabsorption from the later parts of the tubule. Reason (R): ADH release is triggered by an increase in body fluid volume.

• (a) A is true, R is false.
• (b) A is false, R is true.
• (c) Both true.
• (d) Both false.

Answer: (a) Correction: ADH is released when there is a decrease in body fluid volume (osmoreceptors detect high blood osmolarity).

Section 7: Mixed Human Physiology (Rapid Fire)

Q20. Assertion (A): Pneumotaxic center can moderate the functions of the respiratory rhythm center. Reason (R): Neural signal from this center can reduce the duration of inspiration.

• Answer: (a) Both true, R explains A. (By reducing inspiration duration, it alters the respiratory rate).

Q21. Statement I: The organ of Corti is a structure located on the basilar membrane. Statement II: It contains hair cells that act as auditory receptors.

• Answer: (a) Both statements are true. (Ear anatomy, NCERT).

Q22. Assertion (A): The cerebral cortex is referred to as the grey matter. Reason (R): The neuron cell bodies are concentrated here, giving it the greyish appearance.

• Answer: (a) Both true, R explains A. (Myelinated axons form the "white matter" in the inner part).

Q23. Statement I: A steroid hormone acts by generating secondary messengers like $cAMP$. Statement II: Steroid hormones enter the cell and interact with intracellular receptors.

• Answer: (d) Statement I is false, Statement II is true. (Secondary messengers are for protein/peptide hormones).

Q24. Assertion (A): Gout is the inflammation of joints. Reason (R): It is caused due to the accumulation of uric acid crystals.

• Answer: (a) Both true and R explains A.

Q25. Statement I: The juxtaglomerular apparatus (JGA) is a sensitive region formed by cellular modifications in the DCT and the afferent arteriole. Statement II: A fall in GFR activates the JG cells to release renin.

• Answer: (a) Both statements are true.

Q26. Assertion (A): Large intestine has no significant digestive activity. Reason (R): Only some water, minerals, and certain drugs are absorbed in the large intestine.

• Answer: (b) Both are true, but R does not explain why there is no digestion; it just says what does happen (absorption). The lack of digestion is due to the absence of digestive enzymes.

Q27. Statement I: Prolactin regulates the growth of the mammary glands and formation of milk in them. Statement II: TSH stimulates the synthesis and secretion of thyroid hormones from the thyroid gland.

• Answer: (a) Both statements are correct.

Q28. Assertion (A): Every 1000 ml of oxygenated blood delivers 50 ml of $O_2$ to tissues. Reason (R): 100 ml of oxygenated blood delivers 5 ml of $O_2$.

• Answer: (a) Both true, R explains A (Mathematical derivation). $$100 \text{ ml} \rightarrow 5 \text{ ml}$$ $$1000 \text{ ml} \rightarrow 50 \text{ ml}$$

Q29. Statement I: In the skeletal muscle, the calcium is stored in the sarcoplasmic reticulum. Statement II: During muscle contraction, calcium binds with the $T_pC$ subunit of troponin.

• Answer: (a) Both are correct.

Q30. Assertion (A): All copulations lead to fertilization and pregnancy. Reason (R): Fertilization can only occur if the ovum and sperms are transported simultaneously to the ampullary-isthmic junction.

• Answer: (d) Assertion is false, Reason is true. (Not all copulations lead to pregnancy).

Master Table: High-Frequency Key Phrases in NEET Physiology

When solving "Statement-based" questions, look for these "Switch Words" that examiners use to make a statement wrong.

Strategic Tips for Assertion-Reason Questions

1. The "Because" Test: Read the Assertion, add "because" at the end, and then read the Reason. If it makes logical sense, the answer is (a).
2. Independence Check: If both are true but the Reason discusses a different sub-topic within the same chapter, the answer is (b).
3. Fact-Check: 90% of Statement-based questions are direct lines from NCERT. If words like "all," "always," or "only" appear, scrutinize them twice as hard.

NCERT Line-by-Line High-Yield Points

This section provides an exhaustive, granular breakdown of every high-probability line from the NCERT Class 11 Unit 5. These points are curated based on the last 15 years of AIPMT/NEET trends and the latest NTA syllabus.

Chapter 14: Breathing and Exchange of Gases

(Note: Digestion and Absorption has been removed from the latest NTA syllabus; we begin with Respiratory Physiology.)

H3: Mechanism of Breathing and Respiratory Volumes

1. Site of Gas Exchange: The primary sites of exchange of gases are the Alveoli. Exchange also occurs between blood and tissues.
2. Negative Pressure Breathing: Mammals exhibit negative pressure breathing. Inspiration occurs when intra-pulmonary pressure is less than atmospheric pressure.
3. Diaphragm Action: Contraction of the diaphragm increases the volume of the thoracic chamber in the antero-posterior axis.
4. Intercostal Muscles: Contraction of external intercostal muscles lifts up the ribs and the sternum causing an increase in the volume of the thoracic chamber in the dorso-ventral axis.
5. Expiration Process: Relaxation of the diaphragm and the intercostal muscles returns the diaphragm and sternum to their normal positions and reduces the thoracic volume.
6. Forceful Expiration: We have the ability to increase the strength of inspiration and expiration with the help of additional muscles in the abdomen.
7. Spirometer: The volume of air involved in breathing movements can be estimated by using a spirometer which helps in clinical assessment of pulmonary functions. Note: Residual Volume (RV) cannot be measured by a simple spirometer.

H3: Transport of Gases

8. Hemoglobin Saturation: Each hemoglobin molecule can carry a maximum of four molecules of $O_2$.
9. Oxygen-Dissociation Curve: The curve is Sigmoid. A right shift (reduced affinity) is caused by: $\uparrow PCO_2$, $\uparrow H^+$ (lower pH), $\uparrow Temperature$.
10. CO2 Transport Forms:
    • $70%$ as Bicarbonate ($HCO_3^-$).
    • $20-25%$ as Carbamino-hemoglobin.
    • $7%$ in dissolved state through plasma.
11. Carbonic Anhydrase: RBCs contain a very high concentration of this enzyme, and minute quantities are present in the plasma too. It facilitates the reaction: $$CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons HCO_3^- + H^+$$
12. Alveolar Conditions: High $PO_2$, low $PCO_2$, lesser $H^+$ concentration and lower temperature factors are all favourable for the formation of Oxyhemoglobin.
13. Tissue Delivery: Every 100 ml of oxygenated blood can deliver around 5 ml of $O_2$ to the tissues under normal physiological conditions.
14. CO2 Delivery: Every 100 ml of deoxygenated blood delivers approximately 4 ml of $CO_2$ to the alveoli.

Chapter 15: Body Fluids and Circulation

H3: Formed Elements and Blood Groups

15. Plasma Proteins:
    • Fibrinogens: Needed for clotting.
    • Globulins: Involved in defense mechanisms.
    • Albumins: Help in osmotic balance.
16. Erythrocytes (RBCs): Most abundant. A healthy adult man has on average 5 million to 5.5 million of RBCs $mm^{-3}$ of blood.
17. RBC Lifespan: Average lifespan is 120 days, after which they are destroyed in the spleen (graveyard of RBCs).
18. Leukocytes (WBCs): Nucleated and relatively lesser in number (average 6000-8000 $mm^{-3}$).
    • Neutrophils: Most abundant ($60-65%$). Phagocytic.
    • Basophils: Least abundant ($0.5-1%$). Secrete histamine, serotonin, heparin.
    • Eosinophils: ($2-3%$). Resist infections and associated with allergic reactions.
19. Platelets (Thrombocytes): Produced from megakaryocytes (special cells in the bone marrow). Reduction in number leads to clotting disorders.
20. ABO Grouping: Based on the presence or absence of two surface antigens (A and B) on the RBCs.
21. Universal Donor/Recipient: Person with blood group 'O' is universal donor; 'AB' is universal recipient. (Specifically, $O^-$ is donor, $AB^+$ is recipient).
22. Erythroblastosis Fetalis: Occurs when $Rh^{-ve}$ mother carries an $Rh^{+ve}$ fetus. In the second pregnancy, maternal antibodies ($Rh$) destroy fetal RBCs. Prevented by administering anti-Rh antibodies to the mother immediately after the first delivery.

H3: Cardiac Cycle and Regulation

23. SAN (Sino-atrial Node): The "Pacemaker". It can generate the maximum number of action potentials (70-75 $min^{-1}$).
24. Cardiac Output: $Stroke Volume \times Heart Rate$. Average is 5000 mL or 5 Litres in a healthy individual.
25. Heart Sounds: 'Lubb' (1st sound) is associated with closure of tricuspid and bicuspid valves. 'Dupp' (2nd sound) is associated with closure of semilunar valves.
26. ECG Waves:
    • P-wave: Depolarisation of atria.
    • QRS complex: Depolarisation of ventricles.
    • T-wave: Repolarisation of ventricles.
27. Double Circulation: Hepatic portal system carries blood from the intestine to the liver before it is delivered to the systemic circulation.

Chapter 16: Excretory Products and Their Elimination

H3: Nitrogenous Wastes and Kidney Anatomy

28. Ammonotelism: Excreting ammonia. Highly toxic; requires large amounts of water. Examples: Bony fishes, aquatic amphibians.
29. Ureotelism: Excreting urea. Examples: Mammals, terrestrial amphibians, marine fishes.
30. Uricotelism: Excreting uric acid (as pellets or paste). Least toxic; minimum water loss. Examples: Reptiles, birds, land snails, insects.
31. Kidney Position: Last thoracic ($T_{12}$) and third lumbar ($L_3$) vertebra.
32. Nephron Types:
    • Cortical: Loop of Henle is too short and extends only very little into the medulla. (Majority, $85%$).
    • Juxtamedullary: Loop of Henle is very long and runs deep into the medulla. (Crucial for concentrating urine).
33. Vasa Recta: A minute vessel of peritubular capillaries runs parallel to the Henle’s loop forming a ‘U’ shaped vasa recta. It is absent or highly reduced in cortical nephrons.

H3: Urine Formation and Osmoregulation

34. Glomerular Filtration Rate (GFR): Approximately 125 mL/min (180 Litres per day).
35. Ultrafiltration: Blood is filtered through 3 layers: Endothelium of glomerular vessels, epithelium of Bowman’s capsule (Podocytes), and the basement membrane between them.
36. Reabsorption: Nearly 99% of the filtrate has to be reabsorbed by the renal tubules.
37. Proximal Convoluted Tubule (PCT): 70-80% of electrolytes and water are reabsorbed here. Simple cuboidal brush border epithelium increases surface area.
38. Henle’s Loop:
    • Descending limb: Permeable to water but almost impermeable to electrolytes (concentrates filtrate).
    • Ascending limb: Impermeable to water but allows transport of electrolytes (dilutes filtrate).
39. Counter Current Mechanism: Maintained by Henle's loop and Vasa Recta. It increases the osmolarity from the cortex (300 mOsmol/L) to the inner medulla (1200 mOsmol/L).
40. ADH (Vasopressin): Released from Neurohypophysis. It facilitates water reabsorption from DCT and collecting duct, preventing diuresis.
41. JGA and RAAS: Fall in GFR activates Juxtaglomerular cells to release Renin. Renin converts Angiotensinogen to Angiotensin I, then II (a powerful vasoconstrictor).
42. ANF (Atrial Natriuretic Factor): Released by walls of atria in response to high BP. It causes vasodilation and checks the RAAS.

Chapter 17: Locomotion and Movement

H3: Muscle Physiology

43. Fascia: A common collagenous connective tissue layer that holds several muscle bundles (fascicles).
44. Sarcoplasmic Reticulum: Storehouse of calcium ions ($Ca^{2+}$).
45. Myofibril Banding:
    • 'A' Band (Anisotropic): Contains Myosin.
    • 'I' Band (Isotropic): Contains Actin.
46. Sarcomere: The functional unit of contraction; the portion of a myofibril between two successive 'Z' lines.
47. Regulatory Proteins:
    • Tropomyosin: Wraps around Actin.
    • Troponin: In resting state, a subunit of troponin masks the binding sites for myosin on the actin filaments.
48. Sliding Filament Theory: Contraction of a muscle fibre takes place by the sliding of the thin filaments over the thick filaments.
49. Cross-bridge formation: $Ca^{2+}$ binds to Troponin C, moving tropomyosin, allowing Myosin Head (ATPase) to bind to Actin.
50. Red Fibres: High Myoglobin, many mitochondria, depend on aerobic metabolism. (Slow-twitch).
51. White Fibres: Less Myoglobin, fewer mitochondria, high Sarcoplasmic Reticulum, depend on anaerobic metabolism. (Fast-twitch).

H3: Skeletal System and Joints

52. Axial Skeleton: 80 bones. Includes Skull, Vertebral column, Sternum, and Ribs.
53. Skull: Consists of Cranial (8) and Facial (14) bones.
54. Vertebral Column Formula: $C_7 T_{12} L_5 S_{(5)} Co_{(4)}$.
55. Ribs:
    • True ribs: 1st to 7th pairs (attached to sternum).
    • Vertebrochondral (False): 8th, 9th, 10th pairs (attach to 7th rib).
    • Floating ribs: 11th and 12th (not attached ventrally).
56. Joints:
    • Fibrous: No movement (Sutures in skull).
    • Cartilaginous: Limited movement (Between vertebrae).
    • Synovial: Fluid-filled cavity, high mobility.
      • Ball and Socket: Shoulder/Hip.
      • Hinge: Knee/Elbow.
      • Pivot: Atlas/Axis.
      • Gliding: Between Carpals.
      • Saddle: Between Carpal and Metacarpal of thumb.

Chapter 18: Neural Control and Coordination

H3: Neuronal Excitation and Conduction

57. Resting Potential: Axonal membrane is more permeable to $K^+$ and nearly impermeable to $Na^+$. Inner side is negatively charged.
58. Sodium-Potassium Pump: Transports 3 $Na^+$ outwards for 2 $K^+$ into the cell (Active process).
59. Action Potential: Sudden increase in permeability to $Na^+$ leads to influx, causing Depolarisation.
60. Synaptic Cleft: The gap between pre-synaptic and post-synaptic neurons.
61. Chemical Synapse: Neurotransmitters (like Acetylcholine) are released from synaptic vesicles into the cleft.

H3: Central Nervous System (CNS)

62. Forebrain: Consists of Cerebrum, Thalamus, and Hypothalamus.
63. Corpus Callosum: A tract of nerve fibres that connects the two cerebral hemispheres.
64. Hypothalamus: Controls body temperature, urge for eating and drinking. Contains neurosecretory cells.
65. Limbic System: Formed by inner parts of cerebral hemispheres and deep structures like Amygdala and Hippocampus. Involved in emotional behavior and sexual drive.
66. Midbrain: Contains Corpora Quadrigemina (four round swellings).
67. Hindbrain: Pons, Cerebellum (convoluted surface for extra neurons), and Medulla Oblongata.
68. Medulla: Contains centres which control respiration, cardiovascular reflexes, and gastric secretions.
69. Reflex Arc: Requires at least one afferent (sensory) and one efferent (motor) neuron arranged in series.

Chapter 19: Chemical Coordination and Integration

H3: Hypothalamus and Pituitary

70. Pituitary Anatomy:
    • Adenohypophysis: Pars distalis (GH, PRL, TSH, ACTH, LH, FSH) and Pars intermedia (MSH).
    • Neurohypophysis: Pars nervosa (Stores Oxytocin and ADH).
71. Growth Hormone (GH): Over-secretion in adults causes Acromegaly (severe disfigurement of face).
72. Prolactin (PRL): Regulates growth of mammary glands and formation of milk.
73. LH & FSH: In males, LH stimulates androgens; in females, LH induces ovulation of Graafian follicles and maintains Corpus Luteum.

H3: Thyroid, Parathyroid, and Adrenal

74. Thyroid Gland: Needs Iodine. Deficiency causes Goitre and Hypothyroidism (leads to Cretinism in babies).
75. Thyroxine ($T_4$): Regulates Basal Metabolic Rate (BMR) and RBC formation.
76. Parathyroid Hormone (PTH): A hypercalcemic hormone (increases blood $Ca^{2+}$ levels). It stimulates bone resorption.
77. Adrenal Medulla: Secretes Adrenaline (Epinephrine) and Noradrenaline. Known as "Emergency Hormones" or "3F" (Fight, Flight, Fright) hormones.
78. Adrenal Cortex Layers:
    • Zona Reticularis (Inner)
    • Zona Fasciculata (Middle - Glucocorticoids/Cortisol)
    • Zona Glomerulosa (Outer - Mineralocorticoids/Aldosterone)
79. Cortisol: Involved in Gluconeogenesis, anti-inflammatory reactions, and suppressing immune response.
80. Aldosterone: Acts on renal tubules to reabsorb $Na^+$ and water, and excrete $K^+$ and phosphate.

H3: Pancreas and Testis/Ovary

81. Islets of Langerhans:
    • $\alpha$-cells: Glucagon (Hyperglycemic).
    • $\beta$-cells: Insulin (Hypoglycemic).
82. Diabetes Mellitus: Associated with prolonged hyperglycemia, loss of glucose through urine, and formation of harmful ketone bodies.
83. Testosterone: Stimulates spermatogenesis and male secondary sexual characters.
84. Estrogen: Secreted by growing ovarian follicles.
85. Progesterone: Secreted by Corpus Luteum; supports pregnancy and acts on mammary glands to stimulate formation of alveoli (sac-like structures which store milk).

Mnemonic for Human Physiology Cycles

To remember the order of the layers of the Adrenal Cortex (Outer to Inner): Go Find Rex

• G: Glomerulosa (Mineralocorticoids)
• F: Fasciculata (Glucocorticoids)
• R: Reticularis (Androgens)

High-Yield Case Study Worked Example

Problem: A patient shows symptoms of high blood pressure, high glucose in the urine, and a "Moon Face" appearance. Clinical tests show high levels of Cortisol and low ACTH. Identify the likely disorder and the cause.

Step-by-Step Analysis:

1. Identify Symptoms: High glucose + Moon face + High BP = Cushing’s Syndrome.
2. Analyze Hormone Levels: Cortisol is high (Hypercortisolism).
3. Determine Feedback: Normally, high Cortisol should suppress ACTH via negative feedback. Since ACTH is low, the pituitary is functioning correctly by responding to the high cortisol.
4. Pinpoint Location: The problem is likely in the Adrenal Cortex itself (e.g., an adrenal tumor), which is secreting cortisol autonomously regardless of ACTH levels.
5. Conclusion: Primary Hypercortisolism (Cushing’s Syndrome caused by adrenal tumor).

Summary Checklist for NEET Aspirants

• Memorize the 12 pairs of cranial nerves and their nature (Sensory/Motor). (Optional/Extra-NCERT but helpful).
• Understand the difference between Juxtamedullary and Cortical nephrons (Vasa recta presence).
• Be clear on the shift of the Oxygen-dissociation curve (Right shift = Oxygen release).
• Learn the partial pressures ($PO_2$ and $PCO_2$) in Alveoli, Oxygenated blood, and Tissues.
• Identify all 206 bones of the human skeleton by location.

Final High-Yield Tip: NCERT diagrams of the Ear (Organ of Corti) and the Eye (Retina layers) are frequently used for labeling questions. Pay special attention to the order of cells in the Retina: Photoreceptors $\rightarrow$ Bipolar Cells $\rightarrow$ Ganglion Cells (from inside out).

Last-15-Days Revision Plan & Cheat Sheet

Human Physiology accounts for nearly 20-25% of the Biology section in NEET. In these final 15 days, your focus must shift from "reading" to "active recall" and "data consolidation." This section provides a hyper-condensed yet exhaustive roadmap to ensure no mark is left behind.

Phase 1: The 15-Day Countdown Schedule

This schedule follows the 2:1:1 Rule: 2 hours of NCERT re-reading, 1 hour of active recall (tables), and 1 hour of PYQ (Previous Year Questions) analysis.

Phase 2: The Master Enzyme-Substrate-Product Matrix

Understanding the biochemical transformation is crucial for both Digestion and Cellular respiration questions.

Phase 3: The Hormone-Disorder-Symptom Master Table

This is the most frequently tested area in the NEET "Match the Following" section.

Phase 4: Top 100 One-Liners for Active Recall

Mnemonic Flashcards: Focus on "Only," "Best," "First," and "Smallest."

1. Digestion: The maximum number of calories is provided by Fats ($9.45 \text{ kcal/g}$).
2. Digestion: The Sphincter of Boyden guards the opening of the common bile duct.
3. Digestion: Kupffer cells are phagocytic cells located in the liver.
4. Digestion: Glisson’s capsule is the characteristic feature of mammalian liver.
5. Breathing: Solubility of $CO_2$ is 20-25 times higher than $O_2$.
6. Breathing: Pneumotaxic center is located in the Pons Varolii.
7. Breathing: Every 100 ml of deoxygenated blood delivers approx. $4 \text{ ml}$ of $CO_2$ to alveoli.
8. Breathing: Every 100 ml of oxygenated blood delivers approx. $5 \text{ ml}$ of $O_2$ to tissues.
9. Circulation: The SA node is the "Natural Pacemaker," located in the upper right corner of the Right Atrium.
10. Circulation: $CO = SV \times HR$. If $SV = 70 \text{ ml}$ and $HR = 72 \text{ bpm}$, $CO \approx 5040 \text{ ml} \approx 5 \text{ L}$.
11. Circulation: "LUB" sound is due to the closure of AV valves (Tricuspid/Bicuspid).
12. Circulation: "DUB" sound is due to the closure of Semilunar valves.
13. Circulation: QRS complex represents Ventricular Depolarization (Systole).
14. Excretion: GFR (Glomerular Filtration Rate) is $125 \text{ ml/min}$ or $180 \text{ L/day}$.
15. Excretion: Podocytes are cells lining the Bowman’s capsule forming filtration slits.
16. Excretion: PCT (Proximal Convoluted Tubule) reabsorbs 70-80% of electrolytes and water.
17. Excretion: The ascending limb of Henle’s loop is impermeable to water but permeable to electrolytes.
18. Excretion: Urea is added to the interstitium by the thin segment of the ascending limb.
19. Locomotion: The total number of bones in a human adult is 206.
20. Locomotion: The functional unit of contraction is the Sarcomere (region between two Z-lines).
21. Locomotion: $Ca^{2+}$ binds to Troponin C to expose the myosin-binding site on actin.
22. Locomotion: Myasthenia Gravis is an autoimmune disorder affecting the neuromuscular junction.
23. Locomotion: The H-zone is the central part of the thick filament not overlapped by thin filaments.
24. Neural: Resting membrane potential is $-70 \text{ mV}$, maintained by $3Na^+$ out / $2K^+$ in pump.
25. Neural: Depolarization is caused by the rapid influx of $Na^+$ ions.
26. Neural: The Cornea is the non-vascularized part of the eye (transplanted easily).
27. Neural: The Fovea centralis is the point of greatest visual acuity (Only cones present).
28. Neural: The Organ of Corti is the actual receptor organ for hearing.
29. Chemical: Hormones are non-nutrient trace chemicals.
30. Chemical: Steroid hormones (Estrogen, Cortisol) enter the cell and interact with intracellular receptors.
31. Chemical: Peptide hormones (Insulin, Epinephrine) use secondary messengers like $cAMP$ or $IP_3$.
32. Circulation: Erythroblastosis Fetalis occurs when Mother is $Rh^{-}$, Father is $Rh^{+}$, and Fetus is $Rh^{+}$.
33. Circulation: Vitamin K is essential for blood clotting (synthesis of prothrombin).
34. Breathing: Vital Capacity ($VC$) = $ERV + TV + IRV$.
35. Excretion: ANF (Atrial Natriuretic Factor) causes vasodilation to decrease blood pressure.
36. Excretion: Ornithine cycle (Urea cycle) occurs in the Liver.
37. Neural: The limbic system (Amygdala + Hippocampus) controls emotional behavior.
38. Locomotion: The Atlas is the 1st cervical vertebra; it articulates with occipital condyles.
39. Locomotion: Gout is the accumulation of uric acid crystals in joints.
40. Chemical: Melatonin (Pineal gland) regulates the 24-hour diurnal rhythm.
41. Digestion: Chylomicrons are protein-coated fat globules transported into lacteals.
42. Breathing: Occupational Respiratory Disorders include Silicosis and Asbestosis.
43. Circulation: "Heart failure" is not the same as "Heart attack" (Heart failure = heart doesn't pump enough blood).
44. Excretion: Malpighian tubules are excretory organs of insects (Cockroach).
45. Locomotion: Red muscle fibers contain high Myoglobin and mitochondria.
46. Neural: The Aqueduct of Sylvius passes through the Midbrain.
47. Chemical: "Fight or Flight" hormones are Adrenaline and Noradrenaline.
48. Digestion: PEM (Protein Energy Malnutrition) leads to Kwashiorkor and Marasmus.
49. Breathing: $CO_2$ is transported mostly as Bicarbonate (70%).
50. Circulation: Tricuspid valve is between the Right Atrium and Right Ventricle.
51. Excretion: Dialysis fluid has the same composition as plasma minus nitrogenous wastes.
52. Locomotion: Humerus and Pectoral girdle form a Ball and Socket joint.
53. Neural: Night blindness is due to Vitamin A deficiency (Rhodopsin).
54. Chemical: Thymosin (Thymus) plays a major role in T-lymphocyte differentiation.
55. Digestion: The vermiform appendix is a vestigial organ arising from the Caecum.
56. Breathing: Diaphragm and External Intercostals contract during Inspiration.
57. Circulation: Pulmonary vein carries Oxygenated blood.
58. Excretion: JGA (Juxtaglomerular Apparatus) releases Renin when $BP$ falls.
59. Locomotion: Tetany is rapid spasms due to low $Ca^{2+}$ in body fluid.
60. Neural: Medulla Oblongata controls respiration, cardiovascular reflexes, and gastric secretions.
61. Chemical: $CCK$ (Cholecystokinin) acts on Pancreas and Gall bladder.
62. Digestion: Gastrin stimulates the secretion of $HCl$ and Pepsinogen.
63. Breathing: Emphysema is caused by cigarette smoking; alveolar walls are damaged.
64. Circulation: Hepatic portal system carries blood from Intestine to Liver.
65. Excretion: $ADH$ (Vasopressin) facilitates water reabsorption from $DCT$ and Collecting Duct.
66. Locomotion: The Acetabulum is the cavity where the femur head fits.
67. Neural: The Electrical synapse is faster than the chemical synapse.
68. Chemical: Progesterone is the "Pregnancy Hormone" secreted by Corpus Luteum.
69. Digestion: Sucrose is broken down into Glucose + Fructose.
70. Breathing: $O_2$ dissociation curve shifts to the Right with high $pCO_2$ or high Temp (Bohr Effect).
71. Circulation: Chordae Tendineae hold the AV valves in place.
72. Excretion: Human urine is slightly acidic (pH 6.0).
73. Locomotion: The only movable bone in the skull is the Mandible.
74. Neural: Blind spot is where the Optic nerve leaves the eye; no photoreceptors.
75. Chemical: Parathyroid hormone is Hypercalcemic (increases blood $Ca^{2+}$).
76. Digestion: Bile contains no enzymes but helps in emulsification.
77. Breathing: Residual Volume ($RV$) cannot be measured by a Spirometer.
78. Circulation: Single circulation is seen in Fishes.
79. Excretion: Sebaceous glands eliminate sterols and hydrocarbons through sebum.
80. Locomotion: There are 7 Cervical, 12 Thoracic, 5 Lumbar, 1 Sacral, and 1 Coccygeal vertebrae.
81. Neural: Thalamus is a major coordinating center for sensory and motor signaling.
82. Chemical: Oxytocin (Birth hormone) causes uterine contractions.
83. Digestion: Brunner’s glands are found in the Sub-mucosa of the Duodenum.
84. Breathing: Surfactant (Lecithin) prevents the collapse of alveoli.
85. Circulation: Anemia is the reduction of $Hb$ or $RBC$ count.
86. Excretion: Protonephridia (Flame cells) are found in Platyhelminthes.
87. Locomotion: Knee joint is a Hinge joint.
88. Neural: Eustachian tube connects the Middle ear to the Pharynx.
89. Chemical: Glucagon is a Hyperglycemic hormone (increases blood sugar).
90. Digestion: Lactose is Glucose + Galactose.
91. Breathing: $TV$ of a healthy man is approx. $500 \text{ ml}$.
92. Circulation: Total lifespan of $RBC$ is 120 days.
93. Excretion: Uricotelic animals (Birds, Reptiles, Insects) conserve water.
94. Locomotion: The Scapula is located between the 2nd and 7th ribs.
95. Neural: Grey matter is grey due to the presence of cell bodies and dendrites.
96. Chemical: Calcitonin (TCT) is Hypocalcemic.
97. Digestion: Gastric glands have Parietal cells that secrete Intrinsic Factor (for $B_{12}$ absorption).
98. Breathing: Asthma is an allergic reaction causing inflammation of bronchi.
99. Circulation: Standard ECG uses 3 leads (Two wrists, Left ankle).
100. Excretion: $NH_3$ is the most toxic nitrogenous waste and requires large amounts of water.

Phase 5: Worked Numerical Examples

Example 1: Calculating Cardiac Output Question: A person has a heart rate of 75 beats per minute and an end-diastolic volume of 120 ml. If the end-systolic volume is 50 ml, calculate the Cardiac Output ($CO$). Steps:

1. Calculate Stroke Volume ($SV$): $$SV = EDV - ESV = 120 \text{ ml} - 50 \text{ ml} = 70 \text{ ml}$$
2. Calculate Cardiac Output: $$CO = SV \times HR = 70 \text{ ml} \times 75 \text{ bpm} = 5250 \text{ ml/min} = 5.25 \text{ L/min}$$

Example 2: Lung Capacities Question: If $TV = 500 \text{ ml}$, $IRV = 2500 \text{ ml}$, and $ERV = 1100 \text{ ml}$, find the Vital Capacity ($VC$). Steps:

1. Use the formula: $$VC = TV + IRV + ERV$$ $$VC = 500 + 2500 + 1100 = 4100 \text{ ml}$$

Phase 6: The 40-Point Final Checklist

Before entering the exam hall, ensure you have ticked these off mentally:

1. Dental formula for adults (2123/2123) and milk teeth (2102/2102).
2. Difference between Kwashiorkor (Protein only) and Marasmus (Protein + Calories).
3. Role of Enterokinase (activates Trypsinogen).
4. Value of $pO_2$ in deoxygenated blood ($40 \text{ mmHg}$) vs oxygenated ($95 \text{ mmHg}$).
5. Sigmoid shape of the Oxygen dissociation curve.
6. Presence of Carbonic Anhydrase in $RBC$ for $CO_2$ transport.
7. Percentage of $RBC$ in blood (Hematocrit).
8. Functions of different WBCs (Neutrophils - Phagocytic; Eosinophils - Infection).
9. Difference between Open vs Closed circulatory systems.
10. Time of Atrial Systole ($0.1\text{s}$), Ventricular Systole ($0.3\text{s}$), and Joint Diastole ($0.4\text{s}$).
11. Definition of Double Circulation (Systemic + Pulmonary).
12. Location of Meissner’s and Auerbach’s Plexus (enteric nervous system).
13. Steps of Urea Cycle (Ornithine $\rightarrow$ Citrulline $\rightarrow$ Arginine).
14. Structure of Malpighian Corpuscle (Glomerulus + Bowman’s).
15. Differences between Cortical vs Juxtamedullary Nephrons.
16. Components of sweat (Salt, Urea, Lactic acid).
17. RAAS pathway: Renin $\rightarrow$ Angiotensinogen $\rightarrow$ Angiotensin I $\rightarrow$ II.
18. Role of Angiotensin II as a potent vasoconstrictor.
19. Axial vs Appendicular Skeleton count ($80 : 126$).
20. Number of bones in the Ear Ossicles (Malleus, Incus, Stapes).
21. Difference between Synovial, Fibrous, and Cartilaginous joints.
22. Mechanism of Muscle contraction: role of ATP and $Ca^{2+}$.
23. Sliding Filament Theory: A-band remains constant, I-band shortens.
24. White Muscle vs Red Muscle: presence of Myoglobin.
25. Threshold potential for nerve impulse (approx. $-55 \text{ mV}$).
26. Difference between Myelinated (Saltatory conduction) and Non-myelinated fibers.
27. Parts of the Forebrain, Midbrain, and Hindbrain.
28. Function of the Hypothalamus: Thermoregulation, Urge for eating/drinking.
29. Reflex arc components (Receptor $\rightarrow$ Afferent $\rightarrow$ CNS $\rightarrow$ Efferent $\rightarrow$ Effector).
30. The function of Rods (Scotopic/Dim light) vs Cones (Photopic/Color).
31. Direct vs Indirect Hormone Action.
32. Pituitary hormones: $FSH$ and $LH$ targets.
33. Difference between Calcitonin and $PTH$ (Antagonistic).
34. Function of ANF (Vasodilation, lowers $BP$).
35. Erythropoietin source (Kidney) and function ($RBC$ production).
36. Location of Adrenal Cortex zones (G-F-R: Glomerulosa, Fasciculata, Reticularis).
37. Chemical nature of hormones (Catecholamines, Peptides, Steroids, Iodothyronines).
38. Definition of Cardiac Output and Stroke Volume.
39. Recognition of standard ECG wave abnormalities (e.g., enlarged P-wave).
40. Identification of all diagrams in NCERT Human Physiology chapters.

Quick Revision Mnemonics

• Vessels: Away from heart = Artery.
• Heart Valves: LAB RAT
  • Left Atrioventricular = Bicuspid.
  • Right Atrioventricular = Tricuspid.
• Adrenal Cortex Layers (Outer to Inner): GFR (Glomerulosa, Fasciculata, Reticularis). They secrete MGC (Mineralocorticoids, Glucocorticoids, Corticoids/Androgens).
• White Blood Cells (Abundance): Never Let Monkeys Eat Bananas (Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils).
• Wrist Bones (Carpals): She Looks Too Pretty, Try To Catch Her (Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate).