This man just consumed a large meal which will vastly alter the biochemistry of the gut. The S endocrine cells in the duodenum produce the hormone secretin, which increases pancreatic HCO3- secretion in response to the large meal and fatty acids/H+ entering the duodenum from the stomach.
There are 3 types of enteroendocrine cells in the duodenum, and each of them secretes a hormone that acts on the pancreas:
1. I Cells -> cholecystokinin (CCK) -> increase pancreatic secretions
2. S cells -> secretin -> increase pancreatic HCO3- secretion
3. K cells -> gastric inhibitory peptide (GIP) -> increase insulin release
In addition to its action on the pancreas, secretin also decreases gastric acid secretion and increases bile secretion. (Note that CCK and GIP also have additional actions that are discussed elsewhere in detail.) The release of gastric HCl into the duodenum is the most potent stimulator for secretin release. Increased levels of HCO3- act to neutralize gastric acid in the duodenum thereby allowing proper functioning of pancreatic enzymes.
When approaching this question it is best to first conceptualize what the question is asking which is essentially; which of the following could occur in the GI tract after eating a large meal? With this in mind it is most important to rule out the other incorrect answer choices and find the only correct physiological change that could occur after a large meal. In response to the large meal there will be an influx of fatty acids and protons from the stomach which will stimulate secretin release from the S cells. Though many other changes occur none of the other answer choices are correct and are discussed below.
Illustration A summarizes the physiology of the gut. The video is a tutorial of gut physiology.
Answer 1: Gastrin release would likely increase after a meal leading to an INCREASE in proton secretion.
Answer 2: CCK is released from the I cells of the duodenum in response to fatty acids in the duodenum thus release would be INCREASED not decreased.
Answer 4: The vagus nerve plays an important role in sensing stretch and promoting digestion by INCREASING Ach release.
Answer 5: Ghrelin is increased in times of fasting, stimulating hunger and decreased after a large meal leading to a decrease in appetite.
Secretin release is known to increase bicarbonate release from the pancreas. This unique feature allows it to be used as a valuable diagnostic test.. The secretin stimulation test should lead to an increase in release of bicarbonate and a decrease release of H+ but in certain pathologies such as Zollinger-Ellison (ZE) syndrome where gastrin is released by a gastrinoma this does not occur. For this reason it is the most accurate test for ZE syndrome (1).
Nair RJ, Lawler L, Miller MR. Chronic pancreatitis. Am Fam Physician. 2007 Dec 1;76(11):1679-88. Review. PubMed PMID: .
PMID:18092710 (Link to Abstract)