Cardiovascular, respiratory and renal systems sample question 1

the filtered glucose load exceeds the proximal tubule's transport maximum.

Cardiovascular, respiratory and renal systems sample question 2

Fatty stools after long-chain fat meals, while medium-chain fats still reach portal blood

MCAT · Biological and Biochemical Foundations · Biology

Cardiovascular, respiratory and renal systems

Cardiovascular, respiratory and renal systems is part of Biology in the MCAT Biological and Biochemical Foundations section. The questions below are written in the style of the real test, each with the answer and a worked explanation.

Question types you will see here include cardiac output and Starling mechanism, flow, resistance and pressure, hemoglobin saturation and oxygen content and ventilation control and acid-base data.

Common traps: confusing preload with afterload; forgetting that very high rate shortens filling time; reading cardiac output as heart rate alone.

Sample questions

Question 1
Glucose appears in the urine of a patient with poorly controlled diabetes mellitus mainly because:
- A.
  the collecting duct secretes glucose into the urine.
- B.
  glucose transporters in the loop of Henle are destroyed.
- C.
  the filtered glucose load exceeds the proximal tubule's transport maximum.
- D.
  insulin deficiency makes the glomerular filtration barrier more permeable to glucose.
Answer: C. the filtered glucose load exceeds the proximal tubule's transport maximum.
Glucose is filtered freely, and when plasma glucose is high enough the amount filtered saturates the SGLT transporters in the proximal tubule, so the excess stays in the urine. Glucose is normally filtered anyway; the problem is saturation of reabsorption, not increased glomerular permeability or tubular secretion.
Question 2
A disease blocks the lymphatic vessels that drain the small intestine, including the lacteals. Which finding is most likely?
- A.
  Fatty stools after long-chain fat meals, while medium-chain fats still reach portal blood
- B.
  Loss of glucose in the stool, since monosaccharides leave the gut through the lacteals
- C.
  Higher plasma albumin, since protein no longer leaks into the intestinal interstitium
- D.
  Watery diarrhea that stops on a fat-free diet because ileal bile acids are no longer reabsorbed into blood
Answer: A. Fatty stools after long-chain fat meals, while medium-chain fats still reach portal blood
Long-chain fats leave enterocytes as chylomicrons through lacteals, so blocked lymph causes fat malabsorption, while medium-chain fatty acids enter portal blood directly (A). B: glucose enters capillaries and the portal vein. C: blocked lymph traps protein and fluid, causing loss of albumin and edema, not a rise. D: bile acids return via portal blood from the ileum.

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