Human Physiology: Digestion, Breathing, Circulation and Control
Human Physiology covers digestion and absorption, breathing, circulation, excretion, locomotion, neural control and the endocrine system, with emphasis on the quantitative norms the exam favours.
Key values
- Breathing: tidal volume 500 mL, IRV 2500–3000 mL, ERV 1000–1100 mL, residual volume 1100–1200 mL; vital capacity about 3500–4500 mL. The medulla's rhythm centre controls breathing and responds mainly to rising CO2 and H+.
- Circulation: the SA node is the pacemaker; one cardiac cycle lasts 0.8 s; the ECG shows P (atrial depolarisation), QRS (ventricular depolarisation) and T (ventricular repolarisation).
- Excretion: GFR = 125 mL/min ≈ 180 L/day, and about 99% of the filtrate is reabsorbed. The loop of Henle and vasa recta maintain the counter-current gradient; ADH and aldosterone increase water and Na+ reabsorption.
Worked example
Cardiac output = stroke volume × heart rate. With a stroke volume of 70 mL and a heart rate of 72 beats per minute, cardiac output = 70 × 72 = 5040 mL, about 5 litres per minute - roughly the entire blood volume each minute.
Digestion and other systems
- Salivary amylase acts on starch in the mouth; pepsin works at acid pH in the stomach; trypsin and chymotrypsin act in the alkaline small intestine; bile salts emulsify fats.
- Muscle contraction (sliding filament): Ca2+ binds troponin and myosin heads attach to actin; the A band stays constant while the I band shortens.
- Nerve impulse: resting potential about −70 mV, action potential about +30 mV, produced by Na+ influx and restored by the Na+/K+ pump.
Traps
- Vital capacity excludes residual volume.
- Insulin lowers blood glucose; glucagon raises it.
- ADH deficiency causes diabetes insipidus, not mellitus.
- Residual volume is not measurable by simple spirometry.