A group of researchers investigates why individuals who have undergone gastrectomy lose more weight than can be explained by dietary changes alone. They recruit several subjects who have had distal gastrectomy for benign gastric-outlet obstruction for a clinical study. Control subjects with matching baseline weight are also enrolled and are instructed to follow a diet similar to that of the postgastrectomy subjects during the study period. Plasma levels of several hormones are serially measured over 24 hours in both groups. Levels of one of the hormones are shown in the graph below: This profile most likely represents which of the following hormones?

Question

A group of researchers investigates why individuals who have undergone gastrectomy lose more weight than can be explained by dietary changes alone.  They recruit several subjects who have had distal gastrectomy for benign gastric-outlet obstruction for a clinical study.  Control subjects with matching baseline weight are also enrolled and are instructed to follow a diet similar to that of the postgastrectomy subjects during the study period.  Plasma levels of several hormones are serially measured over 24 hours in both groups.  Levels of one of the hormones are shown in the graph below:  This profile most likely represents which of the following hormones?

Quizplus · Accepted Answer

11ec160b_3bd3_7d5b_9249_2b7696e36dce_MD0001_00 The 24-hour hormone levels in the control subjects show increasing secretion leading up to meals, followed by a sharp postprandial drop. However, the subjects who have undergone gastrectomy show lower baseline levels with attenuation of meal-related fluctuations. This pattern suggests that the hormone is likely secreted in the stomach and suppressed by food intake, which is consistent with the secretory pattern of ghrelin. Ghrelin is produced primarily in the stomach in response to fasting; levels surge leading up to meals and fall after eating. Ghrelin stimulates appetite and promotes weight gain. Caloric restriction and falling fat stores lead to increased ghrelin levels (along with decreased leptin and insulin levels), which limits weight loss from dietary modification alone. However, patients who have undergone bariatric procedures that remove a portion of the stomach (eg, roux-en-Y gastric bypass, sleeve gastrectomy) can lose a significant number of ghrelin-secreting cells. This leads to lower ghrelin levels and less stimulation of appetite in response to fasting, promoting weight loss. (Choice A) Cholecystokinin stimulates gallbladder contraction and pancreatic enzyme and bicarbonate secretion. It is secreted in the duodenum and jejunum in response to fat and protein in the intestinal lumen, and levels rise following meals. (Choice B) Gastrin stimulates parietal cell acid production. It is secreted primarily by G cells of the gastric antrum in response to vagal activity, gastric distension, and the presence of amino acids in the gastric lumen. Although gastrin production would be lower in the postgastrectomy subjects, gastrin levels normally rise (not fall) in response to meals. (Choice D) Insulin levels rise rapidly in response to increased blood glucose following meals then gradually fall back to baseline. Insulin is secreted by pancreatic beta cells and would not be drastically reduced following gastrectomy. (Choice E) Leptin is produced primarily by fat cells in response to short-term food intake and long-term adequacy of fat stores. It acts on the hypothalamus to decrease appetite (obesity blunts this action). During fasting states, leptin levels fall. (Choice F) Motilin stimulates smooth muscle contraction in the upper gastrointestinal tract and generally increases gastric motility. Although secretion appears to increase during fasting and decrease following meals, it is produced primarily in the duodenal mucosa rather than the stomach. Educational objective: Ghrelin is produced in the stomach in response to fasting; levels surge leading up to meals and fall after eating. Ghrelin stimulates appetite and promotes weight gain. Patients who have undergone gastrectomy have reduced ghrelin levels, leading to weight loss. __________ References: The impact of laparoscopic sleeve gastrectomy on plasma ghrelin levels: a systematic review. (http://www.ncbi.nlm.nih.gov/pubmed/23794092)

A Group of Researchers Investigates Why Individuals Who Have Undergone