Human Physiology
Human Physiology is the largest part of the paper: digestion, breathing, circulation, excretion, locomotion, neural control and hormones. Expect labelled diagrams (alveolus, nephron, sarcomere, ECG), pathway sequences and quantitative items such as cardiac output and lung volumes.
Core rules
- Digestion: salivary amylase acts on starch at about pH 6.8; pepsin acts on protein in acid; pancreatic trypsin, chymotrypsin and lipase act in alkaline conditions. Absorption is mainly in the ileum - glucose with Na+, fatty acids as chylomicrons into lacteals.
- Breathing: tidal volume 500 mL; vital capacity = ERV + TV + IRV; residual volume about 1100–1200 mL. CO2 travels mostly as bicarbonate; the oxygen dissociation curve shifts right with higher CO2, H+ or temperature (Bohr effect).
- Circulation: SA node is the pacemaker; cardiac output = stroke volume × heart rate. P wave = atrial depolarisation, QRS = ventricular depolarisation, T = ventricular repolarisation.
- Excretion: filtration at the glomerulus, reabsorption in the PCT, counter-current multiplication in the loop of Henle; ADH and RAAS regulate. Inulin measures GFR; glucose appears in urine only above the renal threshold.
- Movement: sliding filament theory - Ca2+ binds troponin, exposing actin-binding sites; the myosin head uses ATP.
- Neural: resting potential about −70 mV (Na+/K+ pump, K+ leak); action potential from Na+ influx; chemical synapses use neurotransmitters.
Worked example
Stroke volume 70 mL, heart rate 75 beats per minute. Cardiac output = 70 × 75 = 5250 mL/min, about 5.25 L/min. If heart rate rises to 100 with unchanged stroke volume, output becomes 7 L/min. Reasoning: multiply, then check units - mL per beat times beats per minute gives mL per minute.
Traps that cost marks
- Saying ADH increases urine volume; it increases water reabsorption, so volume falls.
- Swapping oxytocin (parturition, milk ejection) with prolactin (milk synthesis).
- Reversing the Bohr effect.