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Human Physiology
4.1 Digestive System
Digestion pathway:
| Organ | Enzyme/Juice | Substrate → Product |
|---|---|---|
| Mouth (salivary glands) | Salivary amylase (ptyalin) | Starch → Maltose |
| Stomach | Pepsin (in HCl) | Proteins → Polypeptides |
| Stomach | Gastric lipase | Fats → Fatty acids (partial) |
| Small intestine (pancreas) | Trypsin, chymotrypsin | Polypeptides → Amino acids |
| Small intestine (pancreas) | Pancreatic amylase | Starch → Maltose |
| Small intestine (pancreas) | Pancreatic lipase | Fats → Glycerol + Fatty acids |
| Liver (bile duct) | Bile salts | Emulsify fats (mechanical, not enzymatic) |
| Small intestine (villi) | Maltase, sucrase, lactase | Disaccharides → Monosaccharides |
| Large intestine | Bacteria (flora) | Water absorption; vitamin K and B₁₂ synthesis |
4.2 Blood and Circulatory System
Blood Composition
- Plasma (55%): Water, proteins (albumin, globulins, fibrinogen), glucose, hormones, waste products.
- Red Blood Cells (RBCs/Erythrocytes): Contain haemoglobin — carry O₂. 4.5–5.5 million/mm³ in adults. No nucleus in mature human RBCs. Life span: 120 days. Made in red bone marrow.
- White Blood Cells (WBCs/Leukocytes): Immunity and defence. Types: neutrophils (phagocytosis), lymphocytes (immune response), monocytes, eosinophils, basophils.
- Platelets (Thrombocytes): Blood clotting. Platelet plug + fibrin clot (coagulation cascade — vitamin K dependent).
Blood Groups — ABO System (Karl Landsteiner, 1900 — Nobel Prize 1930)
| Blood Group | Antigens (on RBC) | Antibodies (in plasma) | Can donate to | Can receive from |
|---|---|---|---|---|
| A | A | b (anti-B) | A, AB | A, O |
| B | B | a (anti-A) | B, AB | B, O |
| AB | A + B | None | AB only | All (universal recipient) |
| O | None | a + b | All (universal donor) | O only |
Rh Factor and Pregnancy
About 80% of Indians are Rh+ (Rh antigen present). Rh incompatibility in pregnancy occurs when an Rh- mother carries an Rh+ foetus. Maternal anti-Rh antibodies (formed in second pregnancy) cross the placenta and destroy foetal RBCs, causing haemolytic disease of the newborn. Prevention: Anti-D immunoglobulin injection within 72 hours of delivery.
Heart Function
The heart is a double pump. The right side pumps deoxygenated blood to lungs (pulmonary circulation); the left side pumps oxygenated blood to body (systemic circulation). Normal heart rate: 60–100 bpm. BP: Normal = 120/80 mmHg; Hypertension > 130/80.
4.3 Respiratory System
Breathing mechanism: Diaphragm contracts (flattens) + intercostal muscles contract → thorax volume increases → lung pressure falls below atmospheric → air rushes in (inhalation). Reverse = exhalation.
Gas exchange: O₂ diffuses from alveoli to blood (high pO₂ in alveoli → low pO₂ in capillaries); CO₂ diffuses from blood to alveoli.
Lung capacity (adult):
- Tidal volume = 500 mL (normal breath)
- Vital capacity = ~4,500 mL (maximum)
- Total lung capacity = ~6,000 mL
4.4 Nervous System and Endocrine System
Neuron structure: Cell body (soma) + Dendrites (receive signals) + Axon (transmit signals) + Synaptic terminals. Nerve impulse = action potential. Speed: up to 120 m/s in myelinated fibres.
Key endocrine glands:
| Gland | Hormone | Function |
|---|---|---|
| Hypothalamus | Releasing hormones | Controls pituitary |
| Anterior pituitary | GH, TSH, ACTH, FSH, LH | Growth, thyroid, adrenal, reproductive |
| Thyroid | Thyroxine (T4), T3 | Metabolic rate; iodine deficiency → goitre |
| Pancreas (β cells) | Insulin | Lowers blood glucose; deficiency → Type 1 diabetes |
| Pancreas (α cells) | Glucagon | Raises blood glucose |
| Adrenal medulla | Adrenaline (epinephrine) | "Fight or flight" — HR, BP increase |
| Parathyroid | PTH | Raises blood Ca²⁺ |
| Testes | Testosterone | Male secondary characteristics |
| Ovaries | Oestrogen, Progesterone | Female reproductive cycle |