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Biology · AFCAT

BA01 — Human Anatomy & Physiology

BA01 · AFCAT General Awareness — Biology ★ Must-Master — 60–70% of AFCAT Biology

Every aircraft needs a fit pilot. AFCAT tests human biology because the IAF needs officers who understand the body they put under stress at high altitude. This single chapter contributes the majority of all AFCAT Biology questions. Work through each system in order: job → key parts → disease when it fails.

Quick Focus: SA node = pacemaker; nephron = functional unit of kidney; insulin from beta cells; reflex arc = spinal cord (NOT brain); alveoli = gas exchange site; largest gland = liver; smallest bone = stapes; pituitary = master gland.

Part 1 — Digestive System

1. Digestive System

Digestion breaks complex food into simple absorbable molecules. Each organ adds specific enzymes along the alimentary canal.

Mouth

Secretion

Salivary amylase (ptyalin); pH 7

Action

Starch → Maltose

Key Fact

Digestion starts here

Stomach

Secretion

Gastric juice: HCl + pepsin + mucus

Action

Protein → Peptides; HCl kills bacteria

Key Fact

pH 2; muscular churning

Small Intestine

Secretion

Bile + Pancreatic juice + Intestinal juice

Action

All nutrients digested; absorbed through villi

Key Fact

Main absorption site; villi = surface area

Large Intestine

Secretion

No digestive enzymes

Action

Water & minerals absorbed; faeces formed

Key Fact

Colon absorbs water

Liver

Secretion

Bile production

Action

Glycogen storage; detoxification

Key Fact

Largest gland in body

Pancreas

Secretion

Digestive enzymes (exocrine)

Action

Insulin / Glucagon (endocrine)

Key Fact

Beta cells → insulin; Alpha cells → glucagon

Part 2 — Circulatory System

2. Circulatory System

Blood delivers oxygen, carries hormones, and neutralises pathogens. AFCAT tests blood composition and the famous pulmonary exception.

RBC (Erythrocytes)

Normal Count

4.5–5.5 million / mm³

Function

Carry O₂ via haemoglobin; some CO₂ transport

Key Fact

No nucleus (mature); life span 120 days

WBC (Leukocytes)

Normal Count

5,000–10,000 / mm³

Function

Immunity; fight infection; phagocytosis

Key Fact

Have nucleus; 5 types; count rises during infection

Platelets (Thrombocytes)

Normal Count

1.5–4 lakh / mm³

Function

Blood clotting; prevents excessive blood loss

Key Fact

No nucleus; smallest blood cell; life span 8–10 days

Plasma

Normal Count

55% of blood

Function

90% water; carries food, hormones, fibrinogen

Key Fact

Universal internal transport medium

Heart — 4 Direct AFCAT Facts:

●4 chambers: Right atrium, Right ventricle, Left atrium, Left ventricle

●SA node (Sinoatrial node) in right atrium = natural pacemaker (~72 bpm)

●Double circulation: Pulmonary (heart ↔ lungs) + Systemic (heart ↔ body)

●The trap: Pulmonary artery = deoxygenated blood (away from heart to lungs); Pulmonary vein = oxygenated blood (lungs to heart) — opposite of the normal rule!

Part 3 — Excretory & Respiratory Systems

3. Excretory System — The Nephron

The kidney filters 180 litres of blood plasma daily but produces only ~1.5 L of urine. The functional unit is the nephron (~1 million per kidney).

Stage 1 — Ultrafiltration

Site

Glomerulus inside Bowman's capsule

What Happens

Blood filtered under pressure; water, glucose, urea, salts pass through

Key Point

Proteins STAY in blood (too large to filter)

Stage 2 — Selective Reabsorption

Site

Proximal Convoluted Tubule + Loop of Henle

What Happens

Glucose, amino acids, water, useful salts reabsorbed back into blood

Key Point

Glucose fully reabsorbed; absent in normal urine

Stage 3 — Tubular Secretion

Site

Distal Convoluted Tubule + Collecting duct

What Happens

Extra H⁺, K⁺, NH₃, drugs, excess ions secreted into filtrate

Key Point

Final urine: urea + water + salts + creatinine

4. Respiratory System

Air Pathway: Nose → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli (gas exchange)

●O₂ diffuses: alveolus → capillary → binds haemoglobin → tissues

●CO₂: tissues → blood (bicarbonate) → alveolus → exhaled

●CO danger: Carbon monoxide binds haemoglobin 240× more than O₂ → blocks O₂ transport

Part 4 — Nervous, Endocrine & Skeletal

5. Endocrine System

Pituitary (base of brain)

Hormone(s)

GH, TSH, ADH, FSH, LH, Prolactin

Function

Controls all other endocrine glands

Key Point

Master gland

Thyroid (neck)

Hormone(s)

Thyroxine (T₄), T₃

Function

Regulates metabolism and body growth

Key Point

Iodine needed; deficiency → Goitre

Adrenal (above kidneys)

Hormone(s)

Adrenaline (medulla), Cortisol (cortex)

Function

Fight-or-flight response; stress regulation

Key Point

Adrenaline = emergency hormone

Pancreas

Hormone(s)

Insulin (β-cells), Glucagon (α-cells)

Function

Blood glucose regulation; insulin deficiency → Diabetes

Key Point

Islets of Langerhans; β-cells make insulin

Reflex Arc: Stimulus → Receptor → Sensory neuron → Spinal Cord → Motor neuron → Effector. The brain is NOT involved — you pull your hand from fire BEFORE feeling pain.

6. Skeletal System

Total bones

206 in adults (infant ~270; fuse during development)

Longest bone

Femur (thigh bone) — supports entire body weight

Smallest bone

Stapes (stirrup, middle ear) — ~3 mm; transmits sound

Hardest substance

Tooth enamel (calcium phosphate hydroxyapatite)

Ball-and-socket

Shoulder, Hip — full 360° rotation

Hinge joint

Elbow, Knee — flexion / extension only

Pivot joint

Atlas-axis — allows head rotation left / right

Fixed (suture)

Skull bones — no movement; protects brain

Functions

Support & shape · Protect organs (skull→brain; ribcage→heart+lungs) · Enable movement · RBC production (red marrow) · Ca & P storage

Part 5 — Health & Diseases

7. Diseases & Deficiency Conditions

Malaria

Type

Protozoan

Agent

Plasmodium (P. falciparum worst)

Transmission

Female Anopheles mosquito

Key Fact

Attacks liver + RBCs

Tuberculosis

Type

Bacterial

Agent

Mycobacterium tuberculosis

Transmission

Airborne droplets (cough, sneeze)

Key Fact

BCG vaccine; affects lungs

Typhoid

Type

Bacterial

Agent

Salmonella typhi

Transmission

Contaminated food and water

Key Fact

Widal test for diagnosis

HIV / AIDS

Type

Viral

Agent

Human Immunodeficiency Virus

Transmission

Blood, sexual contact, mother to child

Key Fact

Destroys CD4 T-helper cells

Cholera

Type

Bacterial

Agent

Vibrio cholerae

Transmission

Contaminated water and food

Key Fact

Severe watery diarrhoea; ORS treatment

Vitamin A (Retinol)

Deficiency

Night blindness / Xerophthalmia

Symptom

Cannot see in dim light; dry cornea

Vitamin B₁ (Thiamine)

Deficiency

Beriberi

Symptom

Nerve damage, muscle weakness

Vitamin C (Ascorbic acid)

Deficiency

Scurvy

Symptom

Bleeding gums, poor wound healing

Vitamin D (Calciferol)

Deficiency

Rickets (children) / Osteomalacia (adults)

Symptom

Soft, bent bones; bowed legs

Iodine

Deficiency

Goitre

Symptom

Enlarged thyroid gland in neck

Iron

Deficiency

Iron-deficiency Anaemia

Symptom

Fatigue, pale skin, low RBC count

AFCAT PYQs — Human Anatomy & Physiology

Q1. Which is the functional unit of the kidney?AFCAT PYQ

(a) Nephron

(b) Neuron

(d) Glomerulus

✓ Answer: (a) Nephron

The nephron has ~1 million units per kidney. It performs filtration (glomerulus), reabsorption (PCT + loop of Henle), and secretion (DCT + collecting duct). The glomerulus is one part of the nephron, not the unit itself.

Q2. The natural pacemaker of the human heart is:AFCAT PYQ

(a) AV node

(b) SA node

(d) Purkinje fibres

✓ Answer: (b) SA node

The SA node (sinoatrial node) in the right atrium fires spontaneously at ~72 bpm. Impulse: SA → AV node → Bundle of His → Purkinje fibres. When it fails, a surgical pacemaker is implanted.

Q3. Insulin is produced by which cells?AFCAT PYQ

(a) Acinar cells

(b) Alpha cells

(d) Delta cells

✓ Answer: (c) Beta cells of Islets of Langerhans

Beta (β) cells secrete insulin when blood glucose rises. Alpha cells secrete glucagon (raises glucose). Insulin deficiency → Type 1 Diabetes.

Q4. The pulmonary vein carries:⚡ Tricky

(a) Deoxygenated blood to lungs

(b) Oxygenated blood from lungs to heart

(d) Oxygenated blood to body

✓ Answer: (b) Oxygenated blood from lungs to heart

The pulmonary vein is the exception: it carries oxygenated blood FROM lungs TO the left atrium. The pulmonary artery carries deoxygenated blood from right ventricle TO lungs. AFCAT tests this reversal directly.

Q5. Malaria is transmitted by:AFCAT PYQ

(a) Male Anopheles

(b) Female Anopheles

(d) Housefly

✓ Answer: (b) Female Anopheles mosquito

Only the female Anopheles needs a blood meal for egg production. Dengue = Aedes aegypti. The vector-disease pairing is directly tested in AFCAT.

Quick Memory Chart — BA01

Heart & Blood

SA node = pacemaker (right atrium)
4 chambers; double circulation
RBC: no nucleus; O₂; 120-day life
Pulmonary vein = oxygenated (exception!)
Plasma = 55% blood; 90% water

Hormones & Nerves

Pituitary = master gland
Insulin (β-cells): lowers glucose
Adrenaline: fight-or-flight
Thyroxine: iodine; metabolism
Reflex: spinal cord (NOT brain)

Diseases & Deficiency

Malaria: Plasmodium + female Anopheles
TB: Mycobacterium (airborne)
Scurvy: Vit C | Rickets: Vit D
Goitre: Iodine deficiency
Stapes = smallest bone; Femur = longest

Practice Exercise

E1. Gas exchange in the lungs occurs in the:

(a) Trachea

(b) Bronchi

(d) Pharynx

E2. Which joint allows the greatest range of movement?

(a) Hinge

(b) Pivot

(d) Gliding

Answers:
E1 → (c) Alveoli | E2 → (c) Ball-and-socket [shoulder and hip; full 360°]

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