Anatomy and Physiology
Anatomy and Physiology
This domain tests how organ systems maintain internal stability and how structure supports function - circulation, gas exchange, excretion, neural signalling, and endocrine control.
Core rules
- Homeostasis is maintained mainly by negative feedback: a deviation triggers a response that reduces it. Positive feedback amplifies a change and is rarer, as in oxytocin-driven childbirth.
- Cardiac output = heart rate × stroke volume. The SA node sets the intrinsic rhythm; the autonomic nervous system modulates it.
- Gas exchange depends on partial-pressure gradients and surface area; oxygen binds haemoglobin cooperatively, giving a sigmoid dissociation curve.
- In the nephron, filtration occurs at the glomerulus, selective reabsorption in the proximal tubule, and fine tuning of water and ions in the loop of Henle and collecting duct under ADH and aldosterone.
- Neurons conduct action potentials via ion channels; myelination increases conduction velocity.
Worked example
A person has a heart rate of 75 beats min⁻¹ and a stroke volume of 68 mL. Cardiac output = 75 × 68 = 5,100 mL min⁻¹, or 5.1 L min⁻¹. Reasoning: keep units consistent and convert millilitres to litres at the end. If stroke volume doubles while heart rate is unchanged, output doubles.
Traps
- Arteries carry blood away from the heart, not necessarily oxygenated blood; the pulmonary artery is deoxygenated.
- Partial pressure is not the same as total concentration; haemoglobin saturation depends on pO2.
- Do not describe ADH as adding water; it increases water reabsorption.
- Reflexes can be spinal and do not always require the brain.