A 3-month-old boy is evaluated for large-volume diarrhea and failure to thrive. The patient was born via spontaneous vaginal delivery at 38 weeks gestation. His mother reports that the pregnancy was uncomplicated and there is no family history of gastrointestinal disease. Physical examination shows mild abdominal distension, muscle wasting, and pitting edema. Histochemical evaluation reveals absence of enteropeptidase activity in the proximal intestinal villi. Activity of which of the following substances is most likely impaired in this patient?

Question

A 3-month-old boy is evaluated for large-volume diarrhea and failure to thrive.  The patient was born via spontaneous vaginal delivery at 38 weeks gestation.  His mother reports that the pregnancy was uncomplicated and there is no family history of gastrointestinal disease.  Physical examination shows mild abdominal distension, muscle wasting, and pitting edema.  Histochemical evaluation reveals absence of enteropeptidase activity in the proximal intestinal villi.  Activity of which of the following substances is most likely impaired in this patient?

Quizplus · Accepted Answer

11ec160b_3cc4_1fc9_9249_813ec60b1543_MD0001_00 Although chemical digestion of proteins begins in the stomach, the majority of enzymatic breakdown and absorption occurs in the small intestine. Dietary proteins exist predominately as polypeptides; in order to be absorbed, they must be hydrolyzed to tripeptides, dipeptides, and amino acids. Hydrolysis begins in the stomach with the activation of pepsin by hydrochloric acid; it continues in the proximal small intestine, catalyzed by the pancreatic enzymes trypsin, chymotrypsin, carboxypeptidase, and elastase. Pancreatic enzymes, including trypsin, are secreted in their inactive forms. Enteropeptidase, a duodenal brush border enzyme, is responsible for activation of trypsin from its inactive precursor, trypsinogen. Once active, trypsin functions to cleave peptide bonds in dietary proteins and activate the other pancreatic enzymes. Enteropeptidase deficiency leads to both protein and fat malabsorption as trypsin is required to activate enzymes required for both lipid and protein digestion. The disease causes diarrhea, failure to thrive, and edema (due to hypoproteinemia). (Choice A) Amylase is produced by the salivary glands and pancreas; it catalyzes the hydrolysis of complex carbohydrates to simple sugars. (Choice B) Bile salts are formed through bile acid conjugation with amino acids glycine and taurine. This increases their solubility, allowing them to aid in lipid digestion and absorption through the formation of micelles. (Choice C) Lactase is produced by the intestinal brush border and is responsible for the hydrolysis of lactose to glucose and galactose. Lactase non-persistence commonly develops during mid-childhood, resulting in lactose intolerance. (Choice D) Chief cells of the stomach release the inactive form of pepsin, pepsinogen. Exposure to hydrochloric acid in the stomach activates pepsin, initiating protein digestion. (Choice E) Secretin is a peptide hormone secreted by the S cells of the duodenum; it stimulates the secretion of bicarbonate from the pancreas and inhibits gastric acid secretion in the stomach. Neutralization of the acidic pH of food entering the duodenum from the stomach is necessary for the proper function of pancreatic enzymes. Educational objective: The duodenal brush border enzyme enteropeptidase activates trypsin from its inactive precursor, trypsinogen. Trypsin degrades complex polypeptides to dipeptides, tripeptides, and amino acids while activating other pancreatic enzymes. Enteropeptidase deficiency impairs both protein and fat absorption, leading to diarrhea, failure to thrive, and hypoproteinemia.

A 3-Month-Old Boy Is Evaluated for Large-Volume Diarrhea and Failure