Researchers measure the serum insulin levels of healthy volunteers after equivalent loads of oral and intravenous glucose. The following curves are observed: Which of the following endogenous substances best explains the difference between the curves?

Question

Researchers measure the serum insulin levels of healthy volunteers after equivalent loads of oral and intravenous glucose.  The following curves are observed:  Which of the following endogenous substances best explains the difference between the curves?

Quizplus · Accepted Answer

Incretins are gastrointestinal hormones produced by the gut mucosa that stimulate pancreatic insulin secretion in response to sugar-containing meals. This response is independent of blood glucose levels, and typically occurs prior to any elevation in blood glucose level following a meal. Two hormones with incretin effects are glucagon-like peptide-1 (GLP-1) and gastric inhibitory peptide (glucose-dependent insulinotropic peptide, GIP). Insulin levels will also increase following intravenous administration of glucose due to the sensitivity of the pancreatic beta-cells to increases in blood glucose, but this increase will not be as marked as that seen following oral glucose administration because the effect of incretin is absent. (Choice A) Insulin-like growth factor-1 is produced by the liver in response to stimulation by growth hormone. It functions as a mitogen and as an inhibitor of apoptosis. (Choice C) Somatostatin is produced by cells in the stomach, small bowel and pancreas and inhibits the production and release of most other gastrointestinal hormones, including insulin. (Choice D) Secretin is a hormone produced in the duodenum in response to increased luminal acidity. It stimulates the release of bicarbonate-rich secretions from the pancreas, gallbladder and duodenum. It also increases the activity of cholecystokinin. (Choice E) Cholecystokinin is produced by the duodenum in response to a fat or protein-rich meal. It has many functions including inhibition of further gastric emptying, stimulation of pancreatic enzyme secretion and stimulation of bile production and gallbladder contraction. Educational objective: Incretin functions by stimulating insulin release following oral consumption of glucose. Incretin-stimulated insulin release is independent of the increase in insulin secretion brought on by elevations in the blood glucose level.

Researchers Measure the Serum Insulin Levels of Healthy Volunteers After