Animal Physiology (Nutrition, Respiration, Circulation, Excretion, Nervous and Endocrine Coordination, Locomotion)
Animal Physiology tests how the human body obtains and distributes materials, removes wastes, coordinates responses and moves. Questions often link structure to function and to homeostasis.
Nutrition, respiration and circulation
- Digestion: salivary amylase acts on starch; pepsinogen is activated by HCl; pancreatic trypsin and lipase act in the duodenum; bile emulsifies fats but contains no enzyme. Absorption occurs through ileal villi.
- Breathing: alveoli provide a thin, moist surface; surfactant reduces surface tension. Haemoglobin carries O2; the oxygen dissociation curve shifts right with more CO2 and lower pH (Bohr effect). CO2 is carried mainly as bicarbonate, aided by carbonic anhydrase and the chloride shift.
- Circulation: double circulation; the SA node is the pacemaker; blood pressure is about 120/80 mm Hg. Clotting converts fibrinogen to fibrin.
Excretion, coordination and movement
- The nephron filters at the glomerulus, reabsorbs in the proximal tubule, and concentrates urine via the loop of Henle countercurrent multiplier. ADH increases water reabsorption; aldosterone increases Na+ reabsorption.
- Neurons have a resting potential near −70 mV maintained by the Na+/K+ pump; an action potential is depolarisation followed by repolarisation; synaptic transmission is chemical.
- Hormones act by negative feedback: insulin lowers blood glucose, glucagon raises it; thyroid hormones regulate metabolism; adrenaline prepares for fight-or-flight.
- Muscle contraction follows the sliding-filament model: Ca2+ binds troponin, myosin heads attach to actin, and sarcomeres shorten; the A band stays constant.
Worked example
Cardiac output = stroke volume × heart rate. If stroke volume is 70 mL and heart rate is 72 beats per minute, output = 70 × 72 = 5040 mL/min, about 5 L/min. The reasoning shows that either a larger stroke volume or a faster rate raises output, which is why exercise increases both.
Traps
Bile is not enzymatic; CO2 is mostly transported as bicarbonate; ADH increases water reabsorption; the SA node, not the AV node, sets the rhythm; actin filaments slide rather than shorten.