BC02 — Human Body — Physiology

The SA node in the right atrium initiates each heartbeat. It is called the natural pacemaker. If it fails, the AV node takes over at a slower rate. Artificial pacemakers mimic this function in patients with arrhythmias.

The nephron is the structural and functional unit of the kidney. Each kidney has ~1 million nephrons. The glomerulus is only one component within the nephron — it is the site of ultrafiltration.

The liver is both the largest gland AND the largest internal organ in the human body. Functions include bile production, glycogen storage, detoxification, and synthesis of plasma proteins.

Pepsin is activated by HCl in the stomach and begins protein digestion (proteins → peptides). Salivary amylase starts starch digestion in the mouth. Trypsin acts in the small intestine. Lipase digests fats.

Alveoli are tiny air sacs at the ends of bronchioles with very thin walls and a rich blood supply — the site of external respiration (O₂ in, CO₂ out). The large surface area of ~70 m² (size of a tennis court) enables efficient gas exchange.

Beta cells of the islets of Langerhans produce insulin, which lowers blood glucose by promoting glucose uptake. Alpha cells produce glucagon (raises blood glucose). Deficiency or resistance to insulin causes diabetes mellitus.

A reflex arc uses the spinal cord — NOT the brain — as the integration centre. This allows rapid, automatic responses (e.g., withdrawing a hand from heat). The brain becomes aware only after the reflex has occurred.

O− (O negative) is the universal donor because red blood cells lack A, B, and Rh antigens — compatible with any blood type. AB+ is the universal recipient. This distinction is frequently tested in CDS.

The cerebellum coordinates balance, posture, and fine motor movements — ensuring smooth, precise movements. Damage causes ataxia (loss of coordination). The cerebrum handles intelligence and conscious thought.

Bile is produced by the liver and stored in the gallbladder. Released into the duodenum, it emulsifies fats — breaking large fat globules into smaller ones for easier enzyme digestion. No digestive enzymes; purely physical action.

The pituitary (master gland) secretes tropic hormones that regulate thyroid (TSH), adrenal (ACTH), and gonads (FSH, LH). It is itself regulated by the hypothalamus, which is sometimes called the 'master of the master gland.'

The cerebrum is the largest part of the brain (~85% of brain mass). It is divided into two hemispheres and controls intelligence, memory, sensation, voluntary movement, and language. The cerebellum controls coordination.

Adrenaline from the adrenal medulla triggers fight-or-flight: increased heart rate, dilated pupils, raised blood sugar, redirected blood to muscles. Prepares the body for immediate action under stress.

Ultrafiltration occurs at the glomerulus inside Bowman's capsule. Blood pressure forces water, glucose, urea, and salts out of capillaries into Bowman's capsule — blood cells and large proteins remain in blood.

Normal human body temperature is 37°C (98.6°F), maintained by the hypothalamus (body's thermostat). Fever is defined as above 38°C (100.4°F). Hypothermia is below 35°C.

Platelets (thrombocytes) are cell fragments that initiate blood clotting at the site of injury. They form a plug and trigger the coagulation cascade. Deficiency causes haemophilia or thrombocytopenia.

The small intestine (duodenum + jejunum + ileum) is the main site for both chemical digestion and nutrient absorption. Villi and microvilli increase surface area enormously. Large intestine mainly absorbs water and forms faeces.

Calcitonin is produced by the thyroid gland (parafollicular cells) and lowers blood calcium by inhibiting bone resorption. Its antagonist is Parathyroid Hormone (PTH) from the parathyroid gland, which raises blood calcium.

The femur (thigh bone) is the longest and strongest bone in the human body, constituting about one-quarter of a person's height. The stapes in the middle ear is the smallest bone (~3 mm).

Vitamin A deficiency causes night blindness (difficulty seeing in dim light) and xerophthalmia (dry, ulcerated cornea leading to blindness). Vitamin A is essential for rhodopsin production in rod cells of the retina.