Human and Comparative Physiology: Circulation, Gas Exchange, Excretion, Nervous and Hormonal Coordination
What this domain tests
Physiology questions combine structure and function and ask you to compare systems. Expect diagrams of the heart, nephron, alveolus and reflex arc, plus explanations of homeostasis and negative feedback.
Circulation and gas exchange
- The heart has four chambers and a double circulation: pulmonary to the lungs, systemic to the body. The SA node sets the pace; the left ventricle has the thickest wall.
- Arteries carry blood away from the heart under high pressure, veins return it with valves, and capillaries allow exchange.
- Alveoli have thin walls, a large surface area, a rich blood supply and a moist surface.
- Breathing is controlled by the medulla oblongata, responding mainly to CO₂ levels. Fish gills use counter-current flow; insects use tracheae.
Excretion and coordination
- The nephron filters blood at the glomerulus into Bowman's capsule, then reabsorbs glucose and water. ADH increases water reabsorption from the collecting duct.
- A reflex arc runs: receptor → sensory neuron → spinal cord synapse → motor neuron → effector.
- Hormones act more slowly and for longer than nerve impulses. Insulin lowers blood glucose; glucagon raises it.
Worked example
After a sugary meal, blood glucose rises. The pancreas detects this and secretes insulin, which stimulates the liver to convert glucose to glycogen; blood glucose falls and insulin secretion decreases. Reasoning: this is negative feedback, because the response reverses the original change.
Traps
Saying arteries always carry oxygenated blood (the pulmonary artery does not); placing ADH action on the loop of Henle; putting the brain inside the reflex arc; forgetting ATP in active reabsorption; confusing nervous and hormonal timescales.