Anatomy and Physiology
Anatomy and Physiology tests structure-to-function links across every body system, with the heaviest weight on the cardiovascular, respiratory, renal and endocrine systems.
Core principles
- Homeostasis is maintained mainly by negative feedback: a change triggers a response that reverses the change.
- Levels of organisation: cell → tissue → organ → system → organism.
- The adult skeleton has 206 bones; an infant has about 270, because many bones fuse.
- Muscle types: skeletal (voluntary, striated), smooth (involuntary, non-striated), cardiac (involuntary, striated, intercalated discs).
- The SA node is the pacemaker, firing about 70–80 times per minute.
- Gas exchange occurs across the alveolar membrane by simple diffusion; the diaphragm is the main muscle of inspiration.
- Nephron: filtration at the glomerulus, most reabsorption in the proximal convoluted tubule, secretion, then concentration in the loop of Henle and collecting duct.
Worked example
A resting adult has a heart rate of 72 beats/min and a stroke volume of 70 mL. Cardiac output = HR × SV = 72 × 70 = 5040 mL/min, approximately 5 L/min. Reasoning: rate multiplied by volume per beat gives volume per minute; this explains why severe tachycardia, blood loss or heart failure reduces tissue perfusion.
Traps that cost marks
- Reversing the pulmonary circulation - the pulmonary artery carries deoxygenated blood and the pulmonary vein carries oxygenated blood.
- Confusing insulin (lowers glucose) with glucagon (raises glucose).
- Forgetting that mature red cells have no nucleus and survive about 120 days.
- Quoting adult haemoglobin without sex differences: roughly 13–17 g/dL in men, 12–15 g/dL in women.