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PART II — Answers to All 11 Questions

i. Scope of Anatomy and Physiology

Anatomy is the science that studies the structure and organization of the human body. Its scope includes:

Branch	Focus
Gross (Macroscopic) Anatomy	Body structures visible to the naked eye (organs, muscles, bones)
Microscopic Anatomy (Histology)	Cell and tissue structure under a microscope
Developmental Anatomy (Embryology)	Structural changes from conception to birth
Neuroanatomy	Structure of the nervous system
Radiological Anatomy	Body structures via imaging (X-ray, CT, MRI)
Pathological Anatomy	Structural changes caused by disease
Systemic Anatomy	Study of body by organ systems
Regional Anatomy	Study of body by regions (head, thorax, abdomen)
Surface Anatomy	External landmarks guiding clinical procedures

Physiology is the science that studies the functions and mechanisms of the body. Its scope includes:

Branch	Focus
Cell Physiology	Functions at the cellular level
Systemic Physiology	Functions of specific organ systems (cardiac, renal, respiratory)
Neurophysiology	Nervous system function
Exercise Physiology	Body's response to physical activity
Pathophysiology	Altered function due to disease

Why study both together? Structure and function are inseparable — the shape of the heart (anatomy) determines how it pumps blood (physiology). Understanding one without the other is incomplete. Together they form the foundation of all clinical medicine, nursing, and allied health sciences.

ii. Structure of a Cell Membrane

The cell membrane (plasma membrane) is a thin, pliable, elastic structure only 7.5–10 nanometers thick. Approximate composition: 55% proteins, 25% phospholipids, 13% cholesterol, 4% other lipids, 3% carbohydrates. (Guyton and Hall Textbook of Medical Physiology)

Fluid Mosaic Model

The basic structure is a lipid bilayer — a double layer of lipid molecules covering the entire cell surface, with large globular proteins interspersed throughout.

Lipid Components

Phospholipids (most abundant):
- Have a hydrophilic (water-loving) phosphate head that faces outward (toward water)
- Have a hydrophobic (fat-soluble) fatty acid tail that faces inward (away from water)
- The two layers arrange tail-to-tail in the middle, creating a barrier
- The middle layer is impermeable to water-soluble substances (ions, glucose, urea)
- Fat-soluble substances (O₂, CO₂, alcohol) cross freely
Sphingolipids: Derived from sphingosine; found especially in nerve cells. Functions: protection from harmful environmental factors, signal transmission, adhesion sites for extracellular proteins.
Cholesterol: Dissolved within the bilayer; controls membrane fluidity and permeability

Protein Components

Type	Location	Function
Integral (transmembrane) proteins	Span the full bilayer	Ion channels, carriers, transporters, receptors
Peripheral proteins	Attached to inner or outer surface	Structural support, enzyme activity
Glycoproteins	Outer surface (carbohydrate chains attached)	Cell recognition, immune response

Functions of the Cell Membrane

Selective barrier (controls what enters/exits)
Cell communication (receptors for hormones, neurotransmitters)
Cell recognition (ABO blood group antigens)
Structural integrity

iii. Classification of Tissues with Examples

Tissues are aggregates of cells organized to perform specific functions. There are four primary tissue types: (Histology: A Text and Atlas)

1. Epithelial Tissue

Lines body surfaces, cavities, and organs; covers or secretes
Simple squamous: alveoli of lungs, blood vessel lining
Simple cuboidal: kidney tubules, thyroid follicles
Simple columnar: small intestine lining
Stratified squamous: skin (keratinized), mouth, esophagus
Pseudostratified columnar: trachea, upper respiratory tract
Transitional: urinary bladder

2. Connective Tissue

Connects, supports, and binds organs
Loose connective tissue: dermis, around organs
Dense connective tissue: tendons, ligaments
Cartilage: hyaline (tracheal rings), fibro (intervertebral discs), elastic (ear)
Bone: skeletal system
Blood: circulating connective tissue
Adipose tissue: fat stores, insulation

3. Muscle Tissue

Produces movement via contraction

Type	Location	Control	Striations
Skeletal	Attached to bones	Voluntary	Yes
Cardiac	Heart wall	Involuntary	Yes
Smooth	Walls of hollow organs (gut, vessels)	Involuntary	No

4. Nervous Tissue

Detects stimuli and transmits electrical signals
Neurons: functional unit (sensory, motor, interneurons)
Neuroglia (glial cells): Astrocytes, oligodendrocytes, Schwann cells, microglia — support and protect neurons
Location: brain, spinal cord, peripheral nerves

iv. Types of Joints

Joints are classified into False Joints (Synarthroses) and True Joints (Diarthroses). (General Anatomy and Musculoskeletal System, THIEME Atlas)

A. Fibrous Joints (Synarthroses)

No joint cavity; bones united by fibrous connective tissue.

Sub-type	Description	Example
Sutures	Interlocking edges	Skull bones
Syndesmoses	Bones united by interosseous membrane/ligament	Inferior tibiofibular joint
Gomphoses	Peg-and-socket	Teeth in jaw sockets

B. Cartilaginous Joints (Amphiarthroses)

Bones united by cartilage; slight movement.

Sub-type	Description	Example
Synchondroses	Hyaline cartilage	Epiphyseal growth plates, first rib to sternum
Symphyses	Fibrocartilage	Pubic symphysis, intervertebral discs

C. Synovial Joints (Diarthroses) — Most Mobile

Contain a joint cavity filled with synovial fluid. Features: articular cartilage, synovial membrane, joint capsule.

Type	Movement	Example
Hinge	Flexion/extension (1 axis)	Elbow, knee, ankle
Pivot	Rotation (1 axis)	Atlantoaxial joint, radioulnar joint
Ball and socket	Multi-axial	Shoulder, hip
Condyloid (Ellipsoidal)	Biaxial	Wrist, metacarpophalangeal
Saddle	Biaxial; opposing concave/convex surfaces	Carpometacarpal joint of thumb
Gliding (Plane)	Gliding movement	Intercarpal, intertarsal joints

v. Functions of RBC and WBC

Red Blood Cells (Erythrocytes)

Biconcave disc shape — increases surface area for gas exchange; no nucleus when mature
Primary function: Oxygen transport — Haemoglobin (Hb) binds O₂ in lungs, releases it to tissues
- Each RBC contains ~280 million haemoglobin molecules
- Each Hb molecule carries 4 O₂ molecules
CO₂ transport: ~70% of CO₂ is carried as bicarbonate (HCO₃⁻) via carbonic anhydrase in RBCs; ~23% bound to Hb as carbaminohaemoglobin
Buffer function: Hb acts as a chemical buffer, helping regulate blood pH
Lifespan: ~120 days; destroyed in spleen and liver

White Blood Cells (Leucocytes)

WBCs form the cellular immune defence. Total normal count: 4,000–11,000/mm³

Type	%	Function
Neutrophils	60–70%	First responders; phagocytose bacteria; release enzymes
Eosinophils	2–4%	Fight parasites; modulate allergic reactions
Basophils	0.5–1%	Release histamine and heparin; role in allergy
Lymphocytes	20–30%	T cells: cell-mediated immunity; B cells: produce antibodies
Monocytes	3–8%	Become macrophages; phagocytosis; antigen presentation

vi. Structure of a Lymph Node

(General Anatomy and Musculoskeletal System, THIEME Atlas)

Lymph nodes are small bean-shaped filtering stations located along lymphatic vessels, ranging from 1 mm to 2 cm in diameter. They are key components of the specific immune response, containing T- and B-lymphocytes.

External Structure

Surrounded by a fibrous capsule
Trabeculae (fibrous partitions) extend inward from the capsule, dividing the node into compartments
Afferent lymphatic vessels enter the convex surface (multiple vessels)
Efferent lymphatic vessels exit at the hilum (indented surface); also the entry/exit point for blood vessels

Internal Structure (from outside to inside)

1. Cortex (outer layer)

Contains secondary lymphoid follicles (with germinal centres)
This is the B-lymphocyte region — B cells mature and produce antibodies here
Germinal centres appear pale (site of B cell proliferation)

2. Paracortex (deep cortex)

Located between and below the follicles
T-lymphocyte region — T cells differentiate here
Contains high endothelial venules (HEV) — lymphocytes leave bloodstream and enter the node here

3. Medulla (inner region)

Consists of medullary cords (lymphocytes, macrophages, plasma cells) and medullary sinuses
Lymph from cortical sinuses flows through medullary sinuses to the efferent vessel

Flow of Lymph

Afferent vessels → subcapsular sinus → cortical sinuses → paracortical sinuses → medullary sinuses → efferent vessel at hilum

As lymph passes through these sinuses, it contacts lymph node tissue, allowing filtration of antigens and pathogens and immune activation.

vii. Cardiac Cycle

(Costanzo Physiology, 7th Edition)

The cardiac cycle refers to all the electrical and mechanical events occurring in one complete heartbeat (~0.8 seconds at 75 bpm). It has 7 phases:

Phase	Key Events	ECG	Valves	Heart Sound
A — Atrial Systole	Atria contract; final ventricular filling	P wave	—	S4 (not normally audible)
B — Isovolumetric Ventricular Contraction	Ventricles contract; pressure rises; volume constant (all valves closed)	QRS complex	Mitral valve closes	S1 (lub)
C — Rapid Ventricular Ejection	Pressure peaks; blood ejected rapidly into aorta/pulmonary artery	ST segment	Aortic valve opens	—
D — Reduced Ventricular Ejection	Blood ejected at slower rate; ventricular volume reaches minimum	T wave	—	—
E — Isovolumetric Ventricular Relaxation	Ventricles relax; pressure falls; volume constant (all valves closed)	—	Aortic valve closes	S2 (dub)
F — Rapid Ventricular Filling	Ventricles fill passively from atria	—	Mitral valve opens	S3 (if present = pathological in adults)
G — Reduced Ventricular Filling (Diastasis)	Slow filling; atria filling with blood from veins	—	—	—

Key values (at rest):

Stroke volume: ~70 mL
Cardiac output: ~5 L/min
End-diastolic volume (EDV): ~130 mL
End-systolic volume (ESV): ~60 mL
Ejection fraction (EF) = SV/EDV = 70/130 ≈ 55% (normal ≥55%)

viii. Mechanism of Respiration

Respiration involves two processes: pulmonary ventilation (air movement in/out) and gas exchange.

Pulmonary Ventilation (Breathing Mechanics)

Inspiration (Active process)

The diaphragm contracts (descends ~1.5 cm)
External intercostal muscles contract → ribs elevate and move outward
Thoracic cavity volume increases → intrapulmonary pressure falls below atmospheric pressure
Air flows into the lungs (down the pressure gradient)

In forced inspiration: sternocleidomastoid, scalenes, pectoralis minor also contract

Expiration (Passive at rest)

Diaphragm and intercostals relax
Elastic recoil of lung tissue reduces thoracic volume
Intrapulmonary pressure rises above atmospheric pressure
Air flows out of lungs

In forced expiration: internal intercostals and abdominal muscles contract

Boyle's Law (Underlying Principle)

At constant temperature: P × V = constant. When volume increases → pressure decreases → air flows in.

Gas Exchange

External respiration (lungs):

O₂ diffuses from alveolar air (pO₂ = 104 mmHg) → into pulmonary capillaries (pO₂ = 40 mmHg)
CO₂ diffuses from capillaries (pCO₂ = 45 mmHg) → into alveoli (pCO₂ = 40 mmHg)

Internal respiration (tissues):

O₂ diffuses from blood → into tissue cells (pO₂ = 40 mmHg in tissues)
CO₂ diffuses from cells → into blood

Control of Respiration

Respiratory centre in the medulla oblongata (rhythmicity centre: inspiratory and expiratory neurons)
Apneustic and pneumotaxic centres in pons modulate rhythm
Central chemoreceptors (medulla): respond to rise in pCO₂/fall in pH
Peripheral chemoreceptors (carotid and aortic bodies): respond to fall in pO₂, rise in pCO₂

ix. Digestion in the Stomach

(Basic Medical Biochemistry; Biochemistry, Lippincott)

The stomach stores food, mechanically churns it into chyme, and begins protein and fat digestion.

Gastric Secretions

Secretion	Source	Function
Hydrochloric acid (HCl)	Parietal cells	Creates acidic pH (1.5–3.5); activates pepsinogen; kills microorganisms
Pepsinogen	Chief (zymogenic) cells	Activated by HCl → pepsin; begins protein digestion
Gastric lipase	Chief cells	Digests ~10–15% of dietary fat
Intrinsic factor	Parietal cells	Essential for vitamin B₁₂ absorption in ileum
Mucus	Mucous neck cells	Protects gastric mucosa from HCl and pepsin
Gastrin	G cells (antrum)	Stimulates HCl and pepsinogen secretion

Process of Protein Digestion

Pepsinogen is secreted as an inactive zymogen
HCl converts pepsinogen → pepsin (autocatalytic at pH < 5)
Pepsin cleaves peptide bonds at aromatic amino acids (phenylalanine, tyrosine) → large polypeptides
Digestion continues in the small intestine by pancreatic proteases

Mechanical Digestion

Peristaltic contractions (3 per minute) mix food with gastric juices
Food is broken into small particles → chyme (semi-liquid)
Chyme is released into the duodenum through the pyloric sphincter (controlled release)

Regulation

Cephalic phase: sight, smell, taste → vagal stimulation → gastric secretion begins
Gastric phase: food in stomach → stretch receptors and G cells → increased secretion
Intestinal phase: chyme in duodenum → secretin and CCK inhibit gastric secretion

x. Reflex Action

A reflex is a rapid, automatic, involuntary response to a stimulus that does not require conscious thought.

Reflex Arc — The Pathway

A reflex arc has 5 components:

Receptor → Afferent (sensory) nerve → Nerve centre (spinal cord/brain) → Efferent (motor) nerve → Effector

Component	Function	Example
Receptor	Detects stimulus	Skin stretch receptors, pain receptors
Afferent neuron	Carries impulse to CNS	Sensory nerve fibre (enters dorsal horn)
Nerve centre	Integrates signal	Spinal cord (for spinal reflexes); synapse in grey matter
Efferent neuron	Carries response to effector	Motor nerve fibre (exits ventral horn)
Effector	Produces the response	Muscle (contracts) or gland (secretes)

Types of Reflexes

Classification	Types	Example
By number of synapses	Monosynaptic (1 synapse)	Knee-jerk (patellar) reflex
	Polysynaptic (multiple synapses)	Withdrawal reflex from pain
By location	Spinal reflexes	Flexor withdrawal reflex
	Cranial reflexes	Pupillary light reflex, gag reflex
By nature	Somatic	Muscle contraction
	Autonomic (visceral)	Bladder emptying, heart rate
By origin	Innate (unconditioned)	Suckling reflex in newborns
	Acquired (conditioned)	Pavlov's dog salivation

Knee-Jerk Reflex (Classic Example — Monosynaptic)

Tapping patellar tendon stretches quadriceps muscle
Muscle spindle (receptor) sends impulse via Ia afferent to spinal cord
Directly synapses on alpha motor neuron in anterior horn (L3–L4)
Motor neuron fires → quadriceps contracts → leg extends
Simultaneously, reciprocal inhibition relaxes the hamstrings (interneurons)

Clinical importance: Reflex testing assesses the integrity of spinal cord segments and peripheral nerves.

xi. Functions of the Kidney

The kidneys are paired, bean-shaped organs (each ~11 cm long) located retroperitoneally. They perform several vital functions:

1. Urine Formation and Excretion of Waste Products

Filter ~180 litres of blood/day (GFR ≈ 125 mL/min) through ~1 million nephrons per kidney
Three processes: glomerular filtration → tubular reabsorption → tubular secretion
Excretes: urea (protein metabolism), uric acid (nucleic acid metabolism), creatinine, drugs, toxins

2. Regulation of Body Fluid Volume

Controls water reabsorption via ADH (antidiuretic hormone) from posterior pituitary
More ADH → more water reabsorbed → concentrated urine (small volume)
Less ADH → dilute urine (large volume)

3. Regulation of Electrolytes

Reabsorbs Na⁺, K⁺, Ca²⁺, Cl⁻, HCO₃⁻ as needed
Aldosterone (from adrenal cortex) promotes Na⁺ reabsorption and K⁺ excretion in collecting duct

4. Regulation of Blood Pressure

Releases renin (from juxtaglomerular cells) → activates the Renin–Angiotensin–Aldosterone System (RAAS) → vasoconstriction + Na⁺ retention → ↑ BP

5. Acid–Base Balance

Excretes H⁺ ions in the distal tubule/collecting duct
Reabsorbs HCO₃⁻ (bicarbonate) to buffer blood pH
Secretes NH₄⁺ (ammonium) to buffer H⁺

6. Erythropoiesis (RBC Production)

Peritubular cells produce erythropoietin (EPO) in response to low O₂
EPO stimulates bone marrow to produce RBCs
In chronic kidney disease: EPO deficiency → anaemia of chronic disease

7. Vitamin D Activation

Converts inactive vitamin D (calcidiol/25-OH-D₃) → active calcitriol (1,25-OH₂-D₃)
Calcitriol promotes calcium and phosphate absorption from the gut

8. Gluconeogenesis

During prolonged fasting, kidneys contribute to glucose synthesis from amino acids and lactate

Sources: Guyton and Hall Textbook of Medical Physiology · Costanzo Physiology, 7th Ed. · General Anatomy and Musculoskeletal System (THIEME Atlas) · Histology: A Text and Atlas · Basic Medical Biochemistry, 6th Ed.

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PART I — Answers to All 7 Questions (Attempt any 6)

A. Organization of the Human Body and Homeostasis

Levels of Organization (Simplest → Most Complex)

Level	Description	Example
Chemical	Atoms combine to form molecules	H₂O, glucose, DNA
Cellular	Molecules organize into cells (smallest living unit)	Neuron, RBC, muscle cell
Tissue	Groups of similar cells performing a common function	Epithelial, connective, muscle, nervous tissue
Organ	Two or more tissue types working together	Heart, liver, kidney
Organ System	Group of organs with a common function	Cardiovascular, respiratory, nervous systems
Organism	All organ systems working together	The complete human body

The 11 Organ Systems of the Human Body

System	Major Organs	Principal Functions
Integumentary	Skin, hair, nails	Protection, temperature regulation
Skeletal	Bones, joints, cartilage	Support, movement, mineral storage
Muscular	Skeletal muscles	Movement, posture, heat production
Nervous	Brain, spinal cord, nerves	Control, communication, sensation
Endocrine	Pituitary, thyroid, adrenals	Hormonal regulation, metabolism
Cardiovascular	Heart, blood vessels	Transport of O₂, nutrients, hormones, waste
Lymphatic/Immune	Lymph nodes, spleen, tonsils	Immunity, fluid balance
Respiratory	Lungs, trachea	Gas exchange (O₂ in, CO₂ out)
Digestive	Stomach, intestines, liver	Nutrient digestion and absorption
Urinary	Kidneys, bladder	Waste excretion, fluid/electrolyte balance
Reproductive	Gonads, uterus	Reproduction

Homeostasis

Definition: Homeostasis is the ability of the body to maintain a relatively stable internal environment (temperature, pH, blood glucose, blood pressure) despite continuous changes in the external environment.

Key components of homeostasis:

Receptor (sensor): Monitors a variable (e.g., blood pressure baroreceptors)
Control centre (integrator): Compares the value to the set point (e.g., cardiovascular centre in medulla)
Effector: Carries out a corrective response (e.g., heart, blood vessels)

Types of feedback:

Type	Mechanism	Examples
Negative feedback	Response opposes the stimulus; restores set point	Thermoregulation, blood glucose regulation, blood pressure control
Positive feedback	Response amplifies the stimulus (not truly homeostatic)	Childbirth (oxytocin surge), blood clotting cascade, LH surge at ovulation

Example — Temperature Regulation:

Body temperature rises → thermoreceptors in hypothalamus detect it → hypothalamus (control centre) activates sweating, vasodilation → body cools → temperature returns to 37°C

Homeostatic imbalance leads to disease. Failure of glucose homeostasis → Diabetes mellitus. Failure of blood pressure homeostasis → Hypertension or shock.

B. Structure and Function of Connective Tissue

Connective tissue is the most abundant and widely distributed tissue in the body. It connects, supports, binds, and separates other tissues and organs.

General Characteristics

Cells are sparse and scattered in an extracellular matrix (ECM)
ECM consists of ground substance + protein fibres
Highly vascular (except cartilage and tendons)
Derived from embryonic mesenchyme

Components

1. Cells

Cell	Origin	Function
Fibroblasts	Mesenchyme	Secrete collagen, elastin, and ground substance — most common CT cell
Macrophages	Monocytes	Phagocytosis of debris, pathogens; antigen presentation
Mast cells	Bone marrow	Release histamine (allergy), heparin (anticoagulation)
Adipocytes	Fibroblasts	Fat storage; insulation; energy reserve
Plasma cells	B lymphocytes	Antibody production
Chondrocytes	Mesenchyme	Found in cartilage; maintain cartilage matrix
Osteocytes	Osteoblasts	Found in bone; maintain bone matrix

2. Extracellular Matrix Fibres

Fibre	Protein	Properties	Location
Collagen fibres	Collagen (Type I–IV)	High tensile strength, flexible	Tendons, ligaments, dermis
Elastic fibres	Elastin + fibrillin	Stretch and recoil	Arteries, lung tissue, ligamentum nuchae
Reticular fibres	Type III collagen	Fine mesh-like network	Liver, spleen, lymph nodes, bone marrow

3. Ground Substance: Gel-like material made of proteoglycans and glycoproteins; fills spaces between cells and fibres; allows diffusion of nutrients and wastes.

Classification and Functions

Loose (Areolar) Connective Tissue

Loosely arranged fibres; abundant ground substance
Location: beneath epithelia, around organs, subcutaneous layer
Function: cushioning, nutrient/waste exchange, immune defence

Dense Connective Tissue

Densely packed collagen fibres; few cells
Dense regular: parallel fibres — tendons (muscle to bone), ligaments (bone to bone)
Dense irregular: fibres in all directions — dermis, joint capsules

Cartilage (avascular; cells = chondrocytes in lacunae)

Type	Features	Location
Hyaline	Glassy matrix; fine collagen	Articular surfaces, tracheal rings, costal cartilages
Fibrocartilage	Thick collagen bundles	Intervertebral discs, menisci, pubic symphysis
Elastic	Contains elastic fibres	Ear pinna, epiglottis

Bone (Osseous Tissue)

Calcified matrix (hydroxyapatite — Ca₁₀(PO₄)₆(OH)₂)
Functions: support, protection, calcium storage, haematopoiesis

Blood

Liquid connective tissue; plasma (matrix) + formed elements
Transport medium for O₂, nutrients, hormones, waste

Adipose Tissue

Specialised for fat storage
White adipose: energy storage, thermal insulation
Brown adipose: thermogenesis (especially in newborns)

C. Composition and Function of Blood + Blood Clotting Mechanism

Composition of Blood

Total blood volume in adults: 5–6 litres (7–8% of body weight)

1. Plasma (55% of blood volume)

Component	% of Plasma	Function
Water	91%	Solvent; transports solutes
Plasma proteins	7–8%	Albumin (osmotic pressure), globulins (antibodies), fibrinogen (clotting)
Inorganic salts	0.9%	Electrolyte balance, pH buffer
Nutrients	Trace	Glucose, amino acids, lipids
Hormones, enzymes, gases	Trace	Regulatory functions
Waste products	Trace	Urea, creatinine, bilirubin

2. Formed Elements (45% of blood volume)

Cell	Normal Count	Function
RBC (Erythrocytes)	4.5–5.5 million/mm³	O₂ and CO₂ transport via haemoglobin
WBC (Leucocytes)	4,000–11,000/mm³	Immunity and defence
Platelets (Thrombocytes)	150,000–400,000/mm³	Haemostasis and blood clotting

Functions of Blood

Transport: O₂ (lungs→tissues), CO₂ (tissues→lungs), nutrients, hormones, waste
Regulation: pH (7.35–7.45), body temperature, fluid balance
Protection: WBCs fight infection; antibodies neutralise pathogens; clotting prevents blood loss

Blood Clotting (Coagulation) Mechanism

The goal of haemostasis is to stop bleeding while keeping blood fluid in intact vessels. It occurs in three phases:

Phase 1: Vascular Spasm (Immediate)

Damaged blood vessel contracts reflexively
Reduces blood flow to the site
Lasts seconds to minutes

Phase 2: Platelet Plug Formation (Primary Haemostasis)

Vessel injury exposes subendothelial collagen and von Willebrand factor (vWF)
Platelets adhere to collagen via vWF receptors (adhesion)
Platelets become activated → change shape (spiky) → release ADP, thromboxane A₂, serotonin (activation)
ADP and TXA₂ recruit more platelets → aggregation → loose platelet plug

Phase 3: Coagulation Cascade (Secondary Haemostasis)

The cascade amplifies and reinforces the platelet plug with fibrin strands.

Extrinsic Pathway (faster; triggered by tissue damage):

Tissue Factor (TF / Factor III) released from damaged tissue
TF + Factor VII → activates Factor X

Intrinsic Pathway (slower; triggered by exposed collagen in blood):

Factor XII → XI → IX → VIII → activates Factor X

Common Pathway (both pathways converge here):

Factor X (activated) + Factor V + Ca²⁺ + Phospholipid → Prothrombinase complex
Prothrombinase converts Prothrombin (II) → Thrombin (IIa)
Thrombin converts Fibrinogen (I) → Fibrin (Ia)
Factor XIII (activated by thrombin) cross-links fibrin → stable fibrin clot

EXTRINSIC: Tissue Factor + VII ──┐
                                  ├→ Activate Factor X
INTRINSIC: XII→XI→IX→VIII ───────┘
                                   ↓
                         X + V + Ca²⁺ + PL
                                   ↓
                    Prothrombin → Thrombin
                                   ↓
                    Fibrinogen → Fibrin → Clot

Clot Retraction and Fibrinolysis

Platelet contractile proteins retract the clot, pulling wound edges together
Plasmin (from plasminogen, activated by tPA) dissolves the clot after wound healing

Anticoagulants that prevent unwanted clotting:

Heparin: activates antithrombin III → inhibits thrombin and Xa
Warfarin: inhibits Vitamin K-dependent clotting factors (II, VII, IX, X)
Prostacyclin (PGI₂): released by intact endothelium; inhibits platelet aggregation

D. Anatomy of Heart + Regulation of Blood Pressure

Anatomy of the Heart

External Features:

Cone-shaped muscular organ; size of a clenched fist; weight ~250–350 g
Located in mediastinum, between 2nd and 5th intercostal spaces
Apex points downward-left; base faces upward-right
Enclosed in a double-layered pericardium (fibrous outer + serous inner layers)
Wall layers: Epicardium (visceral pericardium) → Myocardium (cardiac muscle) → Endocardium (inner lining)

Four Chambers:

Chamber	Wall Thickness	Function
Right Atrium	Thin	Receives deoxygenated blood from SVC, IVC, coronary sinus
Right Ventricle	Moderate	Pumps blood to lungs via pulmonary trunk (low pressure)
Left Atrium	Thin	Receives oxygenated blood from 4 pulmonary veins
Left Ventricle	Thick (~3× right)	Pumps blood to entire body via aorta (high pressure)

Chambers are separated by:

Interatrial septum (between atria)
Interventricular septum (between ventricles)
AV valves (between atria and ventricles)

Heart Valves:

Valve	Location	Opens When	Prevents
Tricuspid (Right AV)	Right atrium → right ventricle	Atrial pressure > ventricular	Backflow from RV to RA
Pulmonary (Semilunar)	Right ventricle → pulmonary artery	Ventricular pressure > PA	Backflow from PA to RV
Mitral/Bicuspid (Left AV)	Left atrium → left ventricle	Atrial pressure > ventricular	Backflow from LV to LA
Aortic (Semilunar)	Left ventricle → aorta	Ventricular pressure > aortic	Backflow from aorta to LV

Blood Flow through the Heart:

Body → Superior/Inferior Vena Cava → Right Atrium → Tricuspid valve → Right Ventricle → Pulmonary valve → Pulmonary Artery → Lungs → Pulmonary Veins → Left Atrium → Mitral valve → Left Ventricle → Aortic valve → Aorta → Body

Coronary Circulation:

Right coronary artery (RCA): supplies right heart and inferior left ventricle
Left coronary artery (LCA): divides into Left Anterior Descending (LAD) and Left Circumflex (LCx)

Conducting System:

SA node (pacemaker, 60–100 bpm) → AV node → Bundle of His → Left and Right Bundle Branches → Purkinje fibres

Regulation of Blood Pressure

BP = Cardiac Output (CO) × Peripheral Vascular Resistance (PVR)

Cardiac Output = Heart Rate × Stroke Volume

Short-Term Regulation (Neural — Seconds to Minutes)

Baroreceptor Reflex (Most important rapid regulator):

Baroreceptors in carotid sinus and aortic arch detect stretch (= BP)
Signals sent to cardiovascular centre in medulla oblongata
↑BP → Baroreceptors fire → inhibit sympathetic, activate parasympathetic (vagus) → ↓HR, vasodilation → BP falls
↓BP → Opposite response → ↑HR, vasoconstriction → BP rises

Sympathetic nervous system:

Stimulates heart: ↑HR and contractility → ↑CO
Stimulates arterioles (α₁ receptors) → vasoconstriction → ↑PVR
Stimulates adrenal medulla → epinephrine/norepinephrine release → ↑BP

Chemoreceptors (carotid/aortic bodies): Detect ↓O₂, ↑CO₂ → activate cardiovascular centre → ↑BP

Long-Term Regulation (Hormonal — Hours to Days)

Mechanism	Effect on BP
RAAS (Renin-Angiotensin-Aldosterone System)	Renin → Angiotensin II (vasoconstriction) + Aldosterone (Na⁺/water retention) → ↑BP
ADH (Vasopressin)	↑water reabsorption + vasoconstriction → ↑BP
Atrial Natriuretic Peptide (ANP)	Released by atria when BP↑ → ↑Na⁺/water excretion, vasodilation → ↓BP
Aldosterone	Increases Na⁺ reabsorption → ↑blood volume → ↑BP

E. Respiratory Volumes and Capacities (with Diagram)

Lung volumes are measured by spirometry. There are 4 volumes and 4 capacities (capacities = sum of 2+ volumes).

Lung Volumes

Volume	Abbreviation	Normal Value (adult male)	Definition
Tidal Volume	TV	500 mL	Volume inhaled/exhaled in one normal, quiet breath
Inspiratory Reserve Volume	IRV	3,100 mL	Extra air that can be forcibly inhaled above TV
Expiratory Reserve Volume	ERV	1,200 mL	Extra air that can be forcibly exhaled after normal exhalation
Residual Volume	RV	1,200 mL	Air remaining in lungs after maximal forced exhalation (cannot be exhaled)

Lung Capacities

Capacity	Formula	Normal Value	Definition
Inspiratory Capacity	IC = TV + IRV	3,600 mL	Max air that can be inhaled after a normal exhalation
Functional Residual Capacity	FRC = ERV + RV	2,400 mL	Air remaining after a normal (passive) exhalation
Vital Capacity	VC = TV + IRV + ERV	4,800 mL	Max air that can be exhaled after a maximal inhalation
Total Lung Capacity	TLC = VC + RV	6,000 mL	Total air the lungs can hold at maximal inflation

Spirometry Diagram

         ↑
         │                 ╔═══════╗  ← MAXIMAL INSPIRATION
         │    IRV 3100 mL  ║       ║
 VOLUME  │                 ║  VC   ║  TLC = 6000 mL
  (mL)   │ TV   500 mL  ───╫────╫──╫
         │                 ║    ║  ║
         │    ERV 1200 mL  ╚════╝  ║  ← Normal End Expiration (FRC)
         │                         ║
         │    RV  1200 mL          ╚═  ← MAXIMAL EXPIRATION
         │
         └──────────────────────────→ Time

Clinical Significance

Pattern	Volumes Affected	Diseases
Obstructive	↑RV, ↑FRC, ↓FEV₁/FVC	Asthma, COPD, emphysema
Restrictive	↓TLC, ↓VC, ↓all volumes	Pulmonary fibrosis, obesity, kyphoscoliosis

Dead space volume (150 mL): Air in conducting airways (trachea, bronchi) that does not participate in gas exchange.

Alveolar ventilation = (TV − Dead Space) × Respiratory Rate = (500 − 150) × 12 = 4,200 mL/min

F. Structure and Function of the Nervous System including ANS

Overview

The nervous system is divided into:

Nervous System
├── Central Nervous System (CNS)
│   ├── Brain
│   └── Spinal Cord
└── Peripheral Nervous System (PNS)
    ├── Somatic NS (voluntary)
    └── Autonomic NS (involuntary)
        ├── Sympathetic ("fight or flight")
        └── Parasympathetic ("rest and digest")

Central Nervous System (CNS)

Brain (~1,400 g; 100 billion neurons):

Part	Main Structures	Functions
Cerebrum	4 lobes (frontal, parietal, temporal, occipital); cerebral cortex	Thought, voluntary movement, sensation, language, memory
Cerebellum	Cerebellar hemispheres, vermis	Coordination, balance, fine motor control
Brainstem	Midbrain, pons, medulla oblongata	Vital functions (HR, breathing, BP); cranial nerve nuclei; consciousness
Diencephalon	Thalamus, hypothalamus	Thalamus: relay station; Hypothalamus: homeostasis (temp, hunger, thirst, sleep, hormones)

Spinal Cord:

Extends from foramen magnum to L1/L2
Grey matter (H-shaped): anterior horn (motor neurons), posterior horn (sensory neurons)
White matter: ascending sensory tracts (spinothalamic, dorsal columns) and descending motor tracts (corticospinal)
Functions: relay of sensory/motor signals; spinal reflexes

Peripheral Nervous System (PNS)

Sensory (afferent) nerves: carry signals from receptors → CNS
Motor (efferent) nerves: carry signals from CNS → effectors
12 pairs of cranial nerves + 31 pairs of spinal nerves

Autonomic Nervous System (ANS)

The ANS controls involuntary functions — heart, blood vessels, glands, smooth muscle. (Guyton and Hall Textbook of Medical Physiology)

Structural Comparison

Feature	Sympathetic	Parasympathetic
Origin	Thoracolumbar (T1–L2)	Craniosacral (CN III, VII, IX, X; S2–S4)
Preganglionic neuron	Short	Long
Postganglionic neuron	Long	Short
Ganglion location	Near spinal cord (paravertebral/prevertebral chain)	Near or within target organ
Main NT (postganglionic)	Norepinephrine (adrenergic)	Acetylcholine (cholinergic)

Functional Comparison ("Fight or Flight" vs "Rest and Digest")

Organ	Sympathetic Effect	Parasympathetic Effect
Heart rate	↑ (positive chronotropy)	↓ (vagal slowing)
Heart contractility	↑	↓ (slight)
Blood vessels	Constriction (↑BP)	Dilation (in some)
Bronchi	Dilation (↑airflow)	Constriction
Pupils	Dilation (mydriasis)	Constriction (miosis)
GI motility	↓	↑
Salivary glands	Thick, scanty secretion	Copious watery saliva
Bladder	Retention (relaxes detrusor)	Voiding (contracts detrusor)
Sweat glands	↑ sweating	—
Adrenal medulla	Releases epinephrine/NE	—
Liver	Glycogenolysis (↑blood glucose)	Glycogen synthesis

Key neurotransmitters and receptors:

Sympathetic: Norepinephrine → α₁ (vasoconstriction), α₂, β₁ (heart), β₂ (bronchodilation)
Parasympathetic: Acetylcholine → Muscarinic receptors (M1–M5) at target organs; Nicotinic receptors at all ganglia

G. Endocrine Glands and Their Hormones with Functions

(Guyton and Hall Textbook of Medical Physiology; Costanzo Physiology, 7th Ed.)

The endocrine system communicates via chemical messengers (hormones) released into the bloodstream.

Major Endocrine Glands and Hormones

1. Hypothalamus

Hormone	Function
TRH (Thyrotropin-releasing hormone)	Stimulates TSH and prolactin release from anterior pituitary
CRH (Corticotropin-releasing hormone)	Stimulates ACTH release
GHRH / Somatostatin	Stimulates / inhibits GH release
GnRH	Stimulates LH and FSH release
Dopamine (PIF)	Inhibits prolactin release

2. Anterior Pituitary (Adenohypophysis)

Hormone	Function
GH (Growth hormone)	Stimulates protein synthesis and growth of all tissues; IGF-1 mediates
TSH (Thyroid-stimulating hormone)	Stimulates synthesis and secretion of T₃ and T₄
ACTH (Adrenocorticotropic hormone)	Stimulates cortisol, androgens, and aldosterone from adrenal cortex
FSH (Follicle-stimulating hormone)	♀: follicle development; ♂: spermatogenesis in Sertoli cells
LH (Luteinizing hormone)	♀: ovulation, corpus luteum; ♂: testosterone from Leydig cells
Prolactin	Milk production and breast development
MSH	Melanin synthesis (skin pigmentation)

3. Posterior Pituitary (Neurohypophysis) — stores hormones made in hypothalamus

Hormone	Function
ADH (Vasopressin)	↑water reabsorption in kidneys (↓urine volume); vasoconstriction
Oxytocin	Uterine contractions during labour; milk ejection; social bonding

4. Thyroid Gland

Hormone	Function
T₃ and T₄ (Triiodothyronine, Thyroxine)	↑Metabolic rate; O₂ consumption; heat production; protein/fat/carb metabolism; growth and development
Calcitonin	↓Blood Ca²⁺ by promoting calcium deposition in bone; inhibits osteoclasts

5. Parathyroid Glands

Hormone	Function
PTH (Parathyroid hormone)	↑Blood Ca²⁺: activates osteoclasts, ↑renal Ca²⁺ reabsorption, activates vitamin D

6. Adrenal Glands

Zone/Part	Hormone	Function
Adrenal cortex – Zona Glomerulosa	Aldosterone (mineralocorticoid)	↑Na⁺ reabsorption, ↑K⁺/H⁺ excretion → ↑blood pressure
Adrenal cortex – Zona Fasciculata	Cortisol (glucocorticoid)	↑Blood glucose (gluconeogenesis); anti-inflammatory; stress response; immunosuppression
Adrenal cortex – Zona Reticularis	Androgens (DHEA)	Weak sex hormones; pubic/axillary hair at puberty
Adrenal medulla	Epinephrine & Norepinephrine (catecholamines)	"Fight or flight": ↑HR, ↑BP, ↑blood glucose, bronchodilation

7. Pancreas (Islets of Langerhans)

Cell	Hormone	Function
β cells	Insulin	↓Blood glucose: promotes glucose uptake into cells, glycogen synthesis, lipogenesis
α cells	Glucagon	↑Blood glucose: promotes glycogenolysis, gluconeogenesis in liver
δ cells	Somatostatin	Inhibits insulin and glucagon secretion

8. Gonads

Gland	Hormone	Function
Testes	Testosterone	Male sex characteristics; spermatogenesis; anabolic effects
Ovaries	Oestrogen	Female sex characteristics; endometrial proliferation; bone density
Ovaries	Progesterone	Prepares uterus for implantation; maintains pregnancy

9. Pineal Gland

Hormone	Function
Melatonin	Regulates circadian rhythm (sleep-wake cycle); secreted in darkness

10. Thymus

Hormone	Function
Thymosin	Promotes T-lymphocyte maturation; immune function

Control of Hormone Secretion

Most endocrine glands are controlled by negative feedback loops:

Hypothalamus → (releasing hormone) → Anterior Pituitary → (tropic hormone) → Target Gland → (hormone) → Target tissues + Negative feedback to hypothalamus & pituitary

Example: Low T₄ → Hypothalamus releases TRH → Pituitary releases TSH → Thyroid releases T₄ → T₄ feeds back to inhibit TRH and TSH

Sources: Guyton and Hall Textbook of Medical Physiology · Costanzo Physiology, 7th Ed. · General Anatomy and Musculoskeletal System (THIEME Atlas) · Histology: A Text and Atlas

Note on Part II: All 11 short-answer questions (scope of anatomy, cell membrane, tissues, joints, RBC/WBC, lymph node, cardiac cycle, respiration, digestion, reflex action, kidney function) were answered in full in the previous response. Both parts together provide complete coverage of the entire exam paper.

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