Physiology Flashcards
6 cards from real USMLE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Physiology flashcards as text
A patient with chronic kidney disease has metabolic acidosis, hyperphosphatemia, and hypocalcemia. What secondary complication develops due to low 1,25-dihydroxyvitamin D3?
Answer: Secondary hyperparathyroidism
CKD impairs 1-alpha hydroxylase (kidney), reducing 1,25-OH vitamin D3 production, causing hypocalcemia and secondary hyperparathyroidism with elevated PTH and renal osteodystrophy.
Which hormone directly stimulates osteoclast activity and increases serum calcium and phosphate reabsorption in the kidney?
Answer: PTH (increases calcium, decreases phosphate reabsorption)
PTH activates osteoclasts (indirectly via osteoblasts), increases renal calcium reabsorption, decreases phosphate reabsorption, and stimulates 1-alpha hydroxylase, increasing calcitriol synthesis.
In the autonomic nervous system, which receptor mediates bradycardia when stimulated by the vagus nerve?
Answer: Muscarinic M2 receptor
Vagal parasympathetic stimulation releases acetylcholine that binds M2 muscarinic receptors in the SA node, activating GIRK channels, hyperpolarizing the cell, and slowing heart rate.
A patient has a Cushing reflex (hypertension, bradycardia, and irregular respirations). What does this indicate?
Answer: Increased intracranial pressure threatening brainstem herniation
The Cushing reflex is a late sign of severely elevated ICP causing brainstem ischemia; the hypertension is a compensatory response to maintain cerebral perfusion against rising ICP.
Which change in pulmonary vascular resistance occurs during lung hyperinflation in emphysema?
Answer: Increased pulmonary vascular resistance leading to cor pulmonale
Emphysema destroys alveolar walls and pulmonary capillaries, reducing the vascular bed and increasing resistance; hypoxic vasoconstriction further increases PVR, leading to right heart failure (cor pulmonale).
Erythropoietin (EPO) is produced primarily by which cell type in response to hypoxia?
Answer: Peritubular fibroblasts of the renal cortex
EPO is produced by peritubular fibroblasts (interstitial cells) in the renal cortex in response to hypoxia via HIF-1alpha stabilization, stimulating red blood cell production in the bone marrow.