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USMLE Step 1 Questions
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After an overnight fast, a child eats a breakfast of cornflakes and milk. The amount of trypsinogen in his duodenum increases because the vagus nerve signals the pancreas to increase which of the following?
Correct Answer: B. Exocytosis of preexisting trypsinogen
During the cephalic and gastric phases that occur after the child eats breakfast, secretions from the pancreas have high concentrations of digestive enzymes in the form of inactive precursors, including trypsinogen. The increased amount of trypsinogen in the duodenum is a result of stimulation of acinar cells by vagal input during cephalic phase and vago-vagal reflex secondary to stomach distention.
Degradation of trypsin does not lead to increased trypsinogen within the duodenum.
The rate of trypsinogen activation does not increase the amount of trypsinogen in the duodenum. It only increases the amount of activated trypsinogen or trypsin in the duodenum. Therefore, the actual amount of trypsinogen in the duodenum decreases as the trypsinogen is activated to trypsin.
Transcription of the trypsinogen gene and translation of the trypsinogen mRNA occur within the acinar cells of the exocrine pancreas and these processes increase the amount of trypsinogen within the acinar cells. However, it is the action of the vagus nerve to increase exocytosis of trypsinogen that leads to an increase of trypsinogen within the duodenum.
1. QuestionCategory: Physiology
After an overnight fast, a child eats a breakfast of cornflakes and milk. The amount of trypsinogen in his duodenum increases because the vagus nerve signals the pancreas to increase which of the following?Correct