Human Physiology and Applied Biology: Systems, Absorption and Homeostasis
This domain tests cell and tissue organisation, organ-system functions, digestion and absorption, gas exchange, circulation, excretion, nervous and endocrine control, and reproduction. Applied questions connect physiology to nutrition and health practice.
Core concepts
- Tissues: epithelial, connective, muscular and nervous. Homeostasis maintains stable internal conditions through feedback.
- Digestion: salivary amylase begins starch digestion; pepsin acts on protein in an acidic stomach; pancreatic amylase, lipase and trypsin continue digestion; bile emulsifies fat. Absorption occurs mainly through villi in the small intestine; water is absorbed in the colon.
- Respiration: alveoli provide a thin, moist surface for gas exchange; the diaphragm and intercostals ventilate the lungs.
- Circulation: plasma, red cells (haemoglobin), white cells and platelets; arteries carry blood away from the heart, veins toward it.
- Excretion: the nephron filters, reabsorbs and secretes; the kidney regulates water and electrolytes.
- Endocrine: insulin lowers blood glucose; glucagon raises it; thyroid hormones regulate metabolism; adrenaline supports fight-or-flight.
Worked example
Explain why a person with iron-deficiency anaemia is advised to take lemon with a cereal–pulse meal. Reasoning: non-haem iron from cereals and pulses is poorly absorbed because phytates bind it. Ascorbic acid from lemon reduces ferric iron to the more absorbable ferrous form and forms a soluble complex. Heme iron from meat is absorbed better and is less affected. Tea and excess calcium inhibit absorption. The duodenum is the main absorption site, and haemoglobin synthesis explains the link to anaemia.
Traps
Saying protein digestion begins in the mouth; placing villi in the stomach; claiming insulin raises blood glucose; assuming all arteries carry oxygenated blood (the pulmonary artery does not); confusing filtration with reabsorption in the nephron.
Exam focus
Enzyme–site matching, absorption, blood components, nephron function and hormone actions.