Digestive, immune and reproductive systems sample question 1

Seminiferous tubules, epididymis, vas deferens, ejaculatory duct, urethra, with maturation and motility gained in the epididymis

Digestive, immune and reproductive systems sample question 2

Secretin, which stimulates bicarbonate secretion by the pancreas

Digestive, immune and reproductive systems sample question 3

Secretin, released in response to acid, stimulates pancreatic bicarbonate, and CCK, released in response to fats and amino acids, stimulates enzymes and gallbladder contraction.

Digestive, immune and reproductive systems sample question 4

It stores and concentrates bile made by the liver and contracts when cholecystokinin signals fat in the duodenum.

Digestive, immune and reproductive systems sample question 5

Activation of naive CD4⁺ helper T cells by dendritic cells presenting antigen taken up from outside the cell

MCAT · Biological and Biochemical Foundations · Biology

Digestive, immune and reproductive systems

Digestive, immune and reproductive 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 digestive enzymes, sites and pH, absorption and malabsorption, immune cell roles and antibody response and memory.

Common traps: mixing pepsin's acid optimum with pancreatic enzymes in the duodenum; treating bile as an enzyme; reversing the targets of secretin and CCK.

Sample questions

Question 1
Which sequence correctly describes the path of sperm from the site of production to the urethra, and where they mature and gain motility?
- A.
  Seminiferous tubules, vas deferens, epididymis, ejaculatory duct, urethra, with maturation in the vas deferens
- B.
  Epididymis, seminiferous tubules, vas deferens, urethra, with motility gained in the seminal vesicles
- C.
  Seminiferous tubules, epididymis, ejaculatory duct, vas deferens, urethra, with motility gained in the prostate gland during ejaculation
- D.
  Seminiferous tubules, epididymis, vas deferens, ejaculatory duct, urethra, with maturation and motility gained in the epididymis
Answer: D. Seminiferous tubules, epididymis, vas deferens, ejaculatory duct, urethra, with maturation and motility gained in the epididymis
D is correct: sperm form in the seminiferous tubules, mature and become motile in the epididymis, and pass through the vas deferens and ejaculatory duct to the urethra. A puts the vas deferens before the epididymis; B reverses the first two; C swaps the vas deferens with the ejaculatory duct and credits the prostate with motility.
Question 2
Acidic chyme entering the duodenum triggers release of which hormone, and with what main effect?
- A.
  Secretin, which stimulates contraction of the gallbladder
- B.
  Gastrin, which stimulates bicarbonate secretion by the pancreas
- C.
  Cholecystokinin, which stimulates acid secretion by the stomach
- D.
  Secretin, which stimulates bicarbonate secretion by the pancreas
Answer: D. Secretin, which stimulates bicarbonate secretion by the pancreas
Low duodenal pH triggers S cells to release secretin, which causes pancreatic duct cells to secrete bicarbonate-rich fluid that neutralizes the acid. Gallbladder contraction is triggered mainly by cholecystokinin in response to fats and amino acids, not by secretin.
Question 3
Acidic chyme containing fatty acids and amino acids enters the duodenum. Which statement correctly describes the hormones released?
- A.
  Secretin from I cells stimulates enzyme release by the pancreas, and CCK from S cells stimulates bicarbonate release, and both hormones are released only in response to a rise in plasma glucose.
- B.
  Gastrin from the duodenum increases stomach acid secretion, and secretin inhibits gallbladder contraction.
- C.
  CCK from S cells responds to acid and stimulates bicarbonate secretion, while secretin stimulates bile release.
- D.
  Secretin, released in response to acid, stimulates pancreatic bicarbonate, and CCK, released in response to fats and amino acids, stimulates enzymes and gallbladder contraction.
Answer: D. Secretin, released in response to acid, stimulates pancreatic bicarbonate, and CCK, released in response to fats and amino acids, stimulates enzymes and gallbladder contraction.
Duodenal acid triggers secretin (from S cells), which raises bicarbonate secretion from pancreatic ducts to neutralize the chyme; fatty acids and amino acids trigger CCK (from I cells), which stimulates pancreatic enzymes and gallbladder contraction. A and C swap the hormones' stimuli and effects, and B misassigns gastrin and secretin.
Question 4
A patient has had the gallbladder removed. Which statement correctly describes the normal role of the gallbladder?
- A.
  It makes bile salts from cholesterol and releases them into the duodenum after each meal that the patient eats.
- B.
  It stores and concentrates bile made by the liver and contracts when cholecystokinin signals fat in the duodenum.
- C.
  It secretes pancreatic lipase into the bile duct when cholecystokinin is released.
- D.
  It releases bile in response to secretin, the main signal for fat in the duodenum.
Answer: B. It stores and concentrates bile made by the liver and contracts when cholecystokinin signals fat in the duodenum.
Hepatocytes make bile; the gallbladder holds and concentrates it and squeezes it out when CCK from the duodenum signals fat. After removal, dilute bile reaches the duodenum continuously and large fatty meals may be handled less well. A assigns bile synthesis to the gallbladder; C assigns a pancreatic enzyme to it; D confuses secretin (bicarbonate signal) with CCK.
Question 5
A mouse lacks MHC class II molecules only on its dendritic cells; its B cells, T cells and MHC class I are normal. After infection with a bacterium that stays outside host cells, which response is most impaired?
- A.
  Direct killing of infected cells by CD8⁺ T cells that recognize peptides presented by MHC class I molecules on the surface of infected cells
- B.
  Phagocytosis of the bacterium by neutrophils at the site of infection
- C.
  Production of IgM by B cells that bind the bacterium without T-cell help
- D.
  Activation of naive CD4⁺ helper T cells by dendritic cells presenting antigen taken up from outside the cell
Answer: D. Activation of naive CD4⁺ helper T cells by dendritic cells presenting antigen taken up from outside the cell
Dendritic cells present phagocytosed (extracellular) antigen on MHC II to naive CD4⁺ T cells, linking innate and adaptive immunity; without MHC II they cannot start helper responses, which also limits class switching. MHC I presentation is intact (A), neutrophils are innate cells that do not need MHC II (B), and T-independent IgM responses can occur without helpers (C).

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