Purpose: Self-check on feedback loops, neurons, hormones, kidney function, and glucose regulation.
Score: 0 / 12
Topic 4.1 — Feedback Loops
Question 1
In a negative feedback loop:
Solution: Negative feedback opposes the change (e.g., thermoregulation: high T° → sweating, vasodilation → T° drops). Positive feedback amplifies (e.g., oxytocin in childbirth, blood clotting cascade).
Question 2
Which is an example of POSITIVE feedback?
Solution: In labor, uterine contractions stretch the cervix → oxytocin release → stronger contractions → more stretch → more oxytocin. Cycle terminates with delivery.
Topic 4.2 — Neuron Action Potential
Question 3
A neuron's resting membrane potential is approximately:
Solution: ~−70 mV. Maintained by Na+/K+ pump (3 Na+ out, 2 K+ in per ATP) and selective K+ leak channels. Inside is more negative than outside.
Question 4
During depolarization (rising phase of the action potential):
Solution: At threshold (−55 mV), voltage-gated Na+ channels open. Na+ rushes in → membrane potential rises rapidly to ~+30 mV. Then Na+ channels inactivate and K+ channels open → repolarization.
Question 5
Saltatory conduction in myelinated axons:
Solution: Myelin sheath (Schwann/oligodendrocytes) insulates the axon between Nodes of Ranvier. Action potentials regenerate only at nodes — a "jumping" pattern that speeds conduction up to ~120 m/s.
Topic 4.3 — Hormones & Glucose Regulation
Question 6
After a high-sugar meal, blood glucose rises. The pancreas releases ___, which causes the liver and muscles to ___.
Solution: Beta-cells of pancreatic islets secrete insulin → liver and muscle uptake glucose (GLUT4) and store as glycogen; adipose stores as fat. Lowers blood glucose toward set point (~5 mM). Glucagon (alpha-cells) reverses this when glucose is low.
Solution: Steroids are lipid-soluble and diffuse through the cell membrane. They bind intracellular receptors that translocate to the nucleus and alter transcription. Slow but long-lasting effects. Peptide hormones (insulin, glucagon) bind surface receptors → second messengers (cAMP).
Question 8
A patient has Type 1 diabetes. The most likely underlying issue is:
Solution: Type 1: autoimmune attack on beta-cells; insulin must be supplied exogenously. Type 2: insulin resistance plus relative insulin deficiency, often associated with obesity; managed with diet, exercise, oral agents, sometimes insulin.
Topic 4.4 — Kidney Nephron
Question 9
In the nephron, filtration occurs at:
Solution: Blood pressure forces water and small solutes out of glomerular capillaries into Bowman's capsule (~180 L/day filtrate). Cells and proteins remain in blood.
Question 10
ADH (antidiuretic hormone) acts on the collecting duct to:
Solution: ADH (vasopressin) from posterior pituitary inserts aquaporin-2 channels into collecting-duct cells; more water moves out of filtrate into the medullary interstitium → small volume of concentrated urine. Released when blood osmolarity rises.
Question 11
Glucose appears in the urine when blood glucose exceeds about 10 mM because:
Solution: Normally all filtered glucose is reabsorbed in the proximal tubule via SGLT2/GLUT2 transporters. Above the renal threshold (~10 mM blood glucose), transporters saturate and glucose appears in urine (glucosuria) — a classic sign of uncontrolled diabetes.
Question 12
A drop in blood pressure detected by the kidneys triggers release of ___ from the adrenal cortex, which causes ___.
Solution: Renin-angiotensin-aldosterone system: low BP → renin → angiotensin II → adrenal cortex releases aldosterone → distal tubule and collecting duct increase Na+ reabsorption (water follows) → blood volume and pressure rise.