USMLE Physiology

Question 1

A patient with COPD has pCO2 of 55 mmHg and bicarbonate of 32 mEq/L. What is the acid-base disturbance?

Accepted Answer

Chronic respiratory acidosis with metabolic compensation

Answer

Acute respiratory acidosis

Answer

Metabolic alkalosis with respiratory compensation

Answer

Mixed metabolic and respiratory acidosis

Question 2

Starling forces govern fluid movement across capillary membranes. Which force promotes fluid reabsorption from the interstitium into capillaries?

Accepted Answer

Plasma oncotic pressure (COP)

Answer

Capillary hydrostatic pressure

Answer

Interstitial oncotic pressure

Answer

Lymphatic obstruction

Question 3

The Frank-Starling mechanism states that increased preload leads to increased stroke volume. What is the molecular basis for this?

Accepted Answer

Increased overlap of actin and myosin leads to more cross-bridge formation

Answer

Increased calcium influx

Answer

Decreased afterload

Answer

Increased heart rate

Question 4

During exercise, which physiological change causes oxygen delivery to be increased to working muscles?

Accepted Answer

Rightward shift of the oxygen-hemoglobin dissociation curve

Answer

Leftward shift of the oxygen-hemoglobin dissociation curve

Answer

Increased hemoglobin oxygen affinity

Answer

Decreased 2,3-DPG

Question 5

A patient has syndrome of inappropriate antidiuretic hormone (SIADH). What is the expected urine osmolality?

Accepted Answer

High urine osmolality (>100 mOsm/kg)

Answer

Low urine osmolality (<50 mOsm/kg)

Answer

Isotonic urine

Answer

Variable depending on fluid intake

Question 6

Which segment of the nephron is responsible for the countercurrent multiplication that generates the medullary osmotic gradient?

Accepted Answer

Loop of Henle

Answer

Proximal convoluted tubule

Answer

Distal convoluted tubule

Answer

Collecting duct