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 COPD has pCO2 of 55 mmHg and bicarbonate of 32 mEq/L. What is the acid-base disturbance?
Answer: Chronic respiratory acidosis with metabolic compensation
Chronic respiratory acidosis shows elevated pCO2 (hypoventilation) with appropriately elevated bicarbonate (renal compensation of 3.5 mEq/L per 10 mmHg rise in pCO2), distinguishing chronic from acute forms.
Starling forces govern fluid movement across capillary membranes. Which force promotes fluid reabsorption from the interstitium into capillaries?
Answer: Plasma oncotic pressure (COP)
Plasma oncotic pressure (colloid osmotic pressure from plasma proteins, mainly albumin) draws fluid from the interstitium back into capillaries, counteracting capillary hydrostatic pressure.
The Frank-Starling mechanism states that increased preload leads to increased stroke volume. What is the molecular basis for this?
Answer: Increased overlap of actin and myosin leads to more cross-bridge formation
Stretching myocardial fibers (increased preload) increases actin-myosin overlap and sensitizes troponin C to calcium, increasing cross-bridge formation and contractile force.
During exercise, which physiological change causes oxygen delivery to be increased to working muscles?
Answer: Rightward shift of the oxygen-hemoglobin dissociation curve
Exercise increases CO2, temperature, H+, and 2,3-DPG in working muscles, shifting the O2-Hb dissociation curve rightward (Bohr effect), decreasing hemoglobin affinity and increasing O2 delivery.
A patient has syndrome of inappropriate antidiuretic hormone (SIADH). What is the expected urine osmolality?
Answer: High urine osmolality (>100 mOsm/kg)
In SIADH, excess ADH causes inappropriate water retention and concentrated urine (>100 mOsm/kg, often >300 mOsm/kg) despite low serum osmolality.
Which segment of the nephron is responsible for the countercurrent multiplication that generates the medullary osmotic gradient?
Answer: Loop of Henle
The loop of Henle creates the medullary osmotic gradient through countercurrent multiplication: the descending limb is permeable to water (concentrating tubular fluid) while the ascending limb actively pumps NaCl out.