Physiology of Humans and Animals: Exchange, Transport and Homeostasis
Physiology of Humans and Animals tests how organ systems maintain a stable internal environment and exchange materials. High-value topics are digestion and absorption, gas exchange, circulation, excretion, nervous and endocrine coordination, and homeostasis.
Exchange and transport
- Villi increase surface area; epithelial cells have microvilli; glucose and amino acids absorbed by facilitated diffusion/active transport into blood; fatty acids and glycerol form chylomicrons into lacteals.
- Alveoli: thin walls, large surface area, moist, good blood supply; ventilation and counter-current flow in fish gills maintain diffusion gradients.
- Heart: right side deoxygenated to lungs; left side oxygenated to body; valves prevent backflow; cardiac output = stroke volume × heart rate.
Coordination and homeostasis
- Nervous: receptor → sensory neurone → relay neurone → motor neurone → effector; synapse uses neurotransmitter; reflex arc protects.
- Endocrine: insulin lowers blood glucose by promoting uptake/glycogen; glucagon raises it; ADH increases water reabsorption in collecting duct; negative feedback reverses change.
Worked example: Cardiac output if stroke volume 70 cm3 and heart rate 75 beats min-1: 70×75=5250 cm3 min-1 = 5.25 dm3 min-1. Reasoning: units must match; during exercise both stroke volume and heart rate rise.
Traps: arteries carry blood away from heart, not always oxygenated (pulmonary artery); veins carry toward heart, not always deoxygenated (pulmonary vein); insulin and glucagon are antagonistic; glucose reabsorption in the proximal tubule is by active transport, not diffusion only.