Anatomy and Physiology
What this domain tests
Anatomy and physiology questions ask you to connect structure with function and predict what happens when a system is stressed. Expect homeostasis, directional terminology, and the cardiovascular, respiratory, renal, nervous and endocrine systems.
Core rules
- Organisation runs from cell to tissue to organ to system; function at each level depends on the level below.
- Homeostasis uses negative feedback: a sensor detects change, an integrating centre compares it with a set point, and an effector reverses the change. Positive feedback amplifies change and is usually short-lived, as in labour and clotting.
- Anatomical position is standing, face forward, palms forward. Right and left refer to the patient, not the viewer.
- Directional terms: proximal and distal for limbs; superior and inferior for trunk and head; anterior and posterior; medial and lateral; superficial and deep.
- Cardiac output equals heart rate multiplied by stroke volume. Mean arterial pressure is approximately diastolic pressure plus one third of pulse pressure.
- Gas exchange depends on ventilation, perfusion and diffusion; mismatch in any one causes hypoxaemia.
- The nephron filters, reabsorbs and secretes; the loop of Henle builds the medullary concentration gradient.
Worked example
A resting adult has a heart rate of 80 beats per minute and a stroke volume of 70 mL. Cardiac output is 80 × 70 = 5,600 mL/min, or 5.6 L/min. If haemorrhage halves stroke volume to 35 mL, the heart must raise rate to about 160 beats/min to preserve output. That compensates acutely but increases oxygen demand and shortens diastolic filling. The reasoning is to identify the formula, substitute consistent units, then interpret the physiological cost rather than stopping at the number.
Traps that cost marks
- Reversing afferent and efferent: afferent arrives at the integrating centre; efferent exits.
- Calling the pulmonary artery oxygenated; it carries deoxygenated blood to the lungs.
- Treating negative feedback as bad and positive feedback as good.
- Mixing up the patient's left and right on diagrams.