Question 1

In an experiment,a researcher raises mice under completely germfree conditions so that colonization of their intestine with commensal bacteria cannot occur.In comparison with a conventionally raised animal,the concentration of which of the following would be expected to be increased in the colonic contents of such mice?

A)Butyrate
B)Taurochenodeoxycholic acid
C)Unconjugated bilirubin
D)Immunoglobulin A (IgA)
E)Lithocholic acid

B

Accepted Answer

In germfree mice, there is an increase in primary bile acids like taurochenodeoxycholic acid due to the lack of bacterial conversion to secondary bile acids.

Question 2

A child is brought to a gastroenterologist because of persistent diarrhea,particularly after fatty meals.An extensive workup eventually reveals that the child lacks the ability to synthesize peptide YY.The increased stool volume seen in the child is probably ascribable primarily to abnormally high active secretion of which of the following?

A)Short-chain fatty acids
B)Na⁺
C)K⁺
D)Cl⁻
E)Triglycerides

Accepted Answer

The child's lack of ability to synthesize peptide YY leads to increased active secretion of chloride ions (Cl-) in the intestine, which ultimately increases stool volume and causes diarrhea. Choice D, Cl⁻, represents the formula for chloride ion secretion. Therefore, the increased stool volume seen in the child is primarily ascribable to abnormally high active secretion of Cl-.

Question 3

A college student decides to enter the Peace Corps after graduation and is assigned to teach English in sub-Saharan Africa,where the ambient temperature averages 100 $\degree$ F.During the first few weeks of his stay,he notes copious sweating and mild constipation.His gastrointestinal symptoms are probably due in part to upregulated expression of which of the following transport proteins?

A)Cystic fibrosis transmembrane conductance regulator (CFTR)
B)Electrogenic Na⁺/HCO₃^- cotransporter 1 (NBC1)
C)Apical sodium-dependent bile acid transporter (ABST)
D)Na⁺/K⁺/2Cl^- cotransporter,isoform 1 (NKCC1)
E)Epithelial sodium channel (ENaC)

Epithelial sodium channel (ENaC)

Accepted Answer

The symptoms of copious sweating and mild constipation are consistent with the effects of increased absorption of sodium and water in the colon. This increased absorption is likely due to upregulation of the epithelial sodium channel (ENaC) in the colon. ENaC is responsible for the reabsorption of sodium ions from the lumen of the colon into the epithelial cells, which leads to water retention and dehydration of the fecal matter, causing constipation. The increased absorption of sodium ions also leads to increased intracellular water, making it difficult for sweat glands to secrete sweat, resulting in copious sweating.

Question 4

A 45-year-old woman receiving chemotherapy for breast cancer complains of nausea,abdominal pain,bloody diarrhea,and malnutrition.Her symptoms probably reflect toxic effects of the chemotherapy on which of the following gastrointestinal cell types?

A)Smooth muscle cells
B)Parietal cells
C)Pancreatic acinar cells
D)Hepatocytes
E)Epithelial cells

Accepted Answer

The symptoms described are consistent with gastrointestinal toxicity from chemotherapy. The epithelial cells lining the GI tract are often targeted by chemotherapy drugs, resulting in inflammation and damage to the mucosal lining, leading to symptoms such as nausea, abdominal pain, and bloody diarrhea. Chemotherapy drugs may also interfere with nutrient absorption, contributing to malnutrition.

Question 5

A college student notes that when sitting down to dinner,he is frequently struck by an intense impulse to use the restroom.The proximal signal that triggers the reflex arc promoting this response probably originates in which part of the system involved in the integrated response to a meal?

A)The brain
B)The pharynx
C)The esophagus
D)The stomach
E)The duodenum

Accepted Answer

The stomach is responsible for the initial breakdown of food and stretching of the stomach wall, which can trigger the gastrocolic reflex and the urge to defecate. The other options are not as directly involved in the digestive process or reflex arc related to bowel movements.

Deck 31: The Colonic Phase of the Integrated Response to a Meal