Anatomy and Physiology
What this domain tests
Anatomy and Physiology assesses how organ systems maintain homeostasis, how signals propagate, and how structure supports function. Expect questions on feedback loops, membrane potentials, cardiovascular and respiratory variables, renal handling, and endocrine axes.
Core rules and concepts
- Negative feedback opposes deviation; positive feedback amplifies until an endpoint, such as childbirth or clotting.
- Neurons: resting potential is maintained by K+ leak and Na+/K+ ATPase; depolarization opens voltage-gated Na+ channels; repolarization involves K+ efflux.
- Cardiac output = heart rate × stroke volume.
- Oxygen–hemoglobin affinity shifts right with increased CO2, H+, temperature, and 2,3-BPG (Bohr effect).
- Nephron: filtration in glomerulus, reabsorption in proximal tubule, loop of Henle creates medullary gradient, distal tubule and collecting duct fine-tune under aldosterone and ADH.
- Hormones act via feedback; insulin lowers blood glucose, glucagon raises it.
Worked example
A person has heart rate 75 beats/min and stroke volume 80 mL/beat. Cardiac output = 75 × 80 = 6,000 mL/min = 6 L/min. If stroke volume falls to 60 mL/beat and heart rate rises to 100 beats/min, cardiac output becomes 6 L/min, showing compensation. Reasoning: CO depends on both variables; a rise in one can offset a fall in the other, but not always restore tissue perfusion.
Traps that cost marks
Do not confuse sympathetic (fight-or-flight) with parasympathetic (rest-and-digest). Do not say ADH increases urine volume; it increases water reabsorption. Do not confuse filtration into the nephron with reabsorption back to blood. Do not assume all hormones use negative feedback; oxytocin and labor use positive feedback.