Human Anatomy and Physiology
Human Anatomy and Physiology
This subarea tests how organ systems maintain homeostasis and how nervous, endocrine, circulatory, respiratory, digestive, excretory, immune, and reproductive structures work together. Questions often use feedback loops, transport pathways, and graph or data interpretation rather than isolated labeling.
Core concepts
- Homeostasis: negative feedback reverses a deviation (for example, insulin lowers high blood glucose); positive feedback amplifies a change (for example, oxytocin during childbirth).
- Nervous and endocrine control: neurons use action potentials and neurotransmitters; the endocrine system uses hormones that may be lipid-soluble (intracellular receptors) or water-soluble (membrane receptors). The hypothalamus–pituitary axis links both systems.
- Circulation and respiration: arteries carry blood away from the heart, but not always oxygenated blood-the pulmonary artery carries deoxygenated blood. Gas exchange occurs across alveolar membranes by diffusion; breathing is driven mainly by CO₂/pH-sensitive chemoreceptors.
- Excretion and digestion: the nephron filters blood, reabsorbs useful solutes and water, and secretes wastes; digestion involves mechanical and chemical breakdown, with enzymes specific to pH and substrate.
- Immunity: innate immunity is fast and nonspecific; adaptive immunity uses B cells and T cells, with antibodies marking antigens rather than directly killing cells.
Worked example
After a carbohydrate-rich meal, blood glucose rises. Pancreatic beta cells detect the rise and secrete insulin. Insulin promotes glucose uptake by cells and glycogen synthesis in the liver, so blood glucose falls toward the set point. If blood glucose drops too low, alpha cells secrete glucagon, which promotes glycogen breakdown and gluconeogenesis. This is negative feedback because the response opposes the initial change. A common mistake is to call insulin’s action positive feedback; it is not amplifying hyperglycemia-it is correcting it.
Traps
Do not reverse insulin and glucagon; do not claim all arteries carry oxygenated blood; antibodies do not usually destroy pathogens directly; and the nephron does not normally filter large proteins or blood cells. Also distinguish negative from positive feedback by asking whether the response reverses or amplifies the deviation.