Human Physiology
Human Physiology covers digestion, breathing, circulation, excretion, locomotion, neural control, and endocrine coordination. The exam favours structure-function links and simple calculations involving volumes, pressures, or hormone effects.
Core rules and concepts
- Digestion: salivary amylase acts on starch; pepsin acts on proteins in the stomach; pancreatic enzymes act in the small intestine. Bile emulsifies fats but contains no digestive enzyme. Absorption occurs mainly in the small intestine.
- Breathing: inspiration is active, driven by diaphragm and external intercostal muscles. Oxygen transport depends on haemoglobin; CO₂ is carried mainly as bicarbonate.
- Circulation: the SA node initiates the heartbeat. Cardiac cycle includes atrial and ventricular systole and diastole. Blood pressure is highest in arteries.
- Excretion: the nephron filters, reabsorbs, and secretes. ADH increases water reabsorption in the collecting duct. The loop of Henle creates a medullary osmotic gradient.
- Locomotion: sliding filament theory involves actin and myosin. Neural control uses action potentials and synapses. Endocrine glands release hormones such as insulin, thyroxine, and cortisol.
Worked example
Tidal volume is 500 mL and breathing rate is 12 per minute. Minute ventilation = 500 x 12 = 6,000 mL/min. If dead space is 150 mL, alveolar ventilation = (500 - 150) x 12 = 4,200 mL/min. The reasoning separates air moved from air reaching alveoli.
Traps that cost marks
Bile does not digest fat; it emulsifies it. Inspiration is active, while quiet expiration is largely passive. ADH increases water reabsorption, so diabetes insipidus causes dilute urine. Insulin lowers blood glucose; glucagon raises it.