Human Body Systems
Subject: General Science — Biology | Topic: Human Body Exam: AP Group 2 (APPSC) | Sources: NCERT Class X, Lucent's GS
Introduction
The human body is the highest-yield biology topic for APPSC — expect 3-4 questions spanning digestive, circulatory, nervous, and endocrine systems. Blood groups, hormone-gland matching, and bone/organ facts are heavily tested.
Digestive System
Alimentary canal (9 m): Mouth → Pharynx → Oesophagus → Stomach → Small Intestine → Large Intestine → Rectum → Anus
| Organ | Secretion | Function |
|---|---|---|
| Mouth | Salivary amylase (ptyalin) | Digests starch → maltose (pH ~6.8) |
| Oesophagus | — | Peristalsis moves food |
| Stomach | HCl + Pepsin + Mucus | Kills bacteria (pH ~1.5-2), digests proteins |
| Small intestine (7.5 m) | Bile (liver), pancreatic juice, intestinal juice | Complete digestion; villi absorb nutrients |
| Large intestine | — | Absorbs water and electrolytes; forms faeces |
- Liver: Largest internal organ. Produces bile, stores glycogen, detoxifies blood, produces urea.
- Pancreas: Trypsin (proteins), lipase (fats), amylase (starch).
Respiratory System
Path: Nostrils → Nasal cavity → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli
- Alveoli: Gas exchange. Thin walls, ~70 m² surface area, rich blood supply.
- Diaphragm: Contracts (flattens) during inhalation, relaxes during exhalation.
- Cellular respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP (in mitochondria).
- Anaerobic: In muscles → lactic acid (cramps). In yeast → ethanol + CO₂ (fermentation).
- Haemoglobin in RBCs carries O₂ (oxyhaemoglobin).
Circulatory System
Heart: 4 chambers — 2 atria (upper), 2 ventricles (lower). Beats ~72 times/min.
Double circulation:
- Pulmonary: Right ventricle → Lungs → Left atrium
- Systemic: Left ventricle → Body → Right atrium
| Vessel | Carries | Walls | Features |
|---|---|---|---|
| Arteries | Oxygenated blood (except pulmonary artery) | Thick | High pressure |
| Veins | Deoxygenated blood (except pulmonary vein) | Thin | Have valves |
| Capillaries | Exchange gases/nutrients | One cell thick | Site of exchange |
Blood components: Plasma (55%), RBCs (O₂ transport), WBCs (immunity), Platelets (clotting).
Blood Groups: A, B, AB, O. Universal donor: O−. Universal recipient: AB+.
Normal BP: 120/80 mmHg. Hypertension: >140/90.
Excretory System
- Kidneys (pair): Bean-shaped. Each has ~1 million nephrons (functional unit).
- ~180 L filtrate/day → ~1.5 L urine excreted.
- Dialysis: Artificial blood filtration when kidneys fail.
Nervous System
Brain: Cerebrum (thinking, memory) | Cerebellum (balance) | Medulla oblongata (heartbeat, breathing — involuntary).
Neuron: Cell body + Dendrites (receive) + Axon (transmit). Signal: electrical impulse; chemical at synapse.
Reflex arc: Receptor → Sensory nerve → Spinal cord → Motor nerve → Effector (quick, involuntary).
Endocrine System (Hormones)
| Gland | Hormone | Function | Deficiency |
|---|---|---|---|
| Pituitary (master gland) | Growth hormone | Controls growth and other glands | Dwarfism/Gigantism |
| Thyroid | Thyroxine (T4) | Regulates metabolism; needs iodine | Goitre |
| Parathyroid | Parathormone | Regulates calcium | Tetany |
| Adrenal | Adrenaline | Fight-or-flight response | — |
| Pancreas | Insulin (beta cells) | Lowers blood sugar | Diabetes |
| Pancreas | Glucagon (alpha cells) | Raises blood sugar | — |
| Testes | Testosterone | Male secondary sexual characteristics | — |
| Ovaries | Estrogen, Progesterone | Female characteristics, menstrual cycle | — |
Hypothalamus: Links nervous and endocrine systems; controls pituitary.
Skeletal and Muscular System
- Human skeleton: 206 bones. Longest: Femur (thigh). Smallest: Stapes (ear).
- Muscle types: Skeletal/striated (voluntary), Smooth (involuntary — stomach, intestine), Cardiac (involuntary — heart only, never tires).
Sense Organs
- Eye: Lens forms inverted image on retina (rods for dim light, cones for colour).
- Ear: Ossicles (hammer, anvil, stirrup — smallest bones). Cochlea (hearing), Semicircular canals (balance).
- Skin: Largest organ. Protection, temperature regulation, sensation.
Likely Exam Questions
-
The largest internal organ of the human body is: Ans: Liver
-
The universal blood donor group is: Ans: O negative (O−)
-
The functional unit of the kidney is: Ans: Nephron
-
The hormone insulin is secreted by: Ans: Beta cells of the pancreas
-
The longest bone in the human body is: Ans: Femur (thigh bone)
-
The smallest bone in the body is: Ans: Stapes (in the ear)
-
Deficiency of iodine causes: Ans: Goitre (swelling of thyroid gland)
-
The number of bones in the adult human skeleton is: Ans: 206
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The master gland of the endocrine system is: Ans: Pituitary gland
-
Normal blood pressure is: Ans: 120/80 mmHg