Functions of cholecystokinin are all except
**Core Concept**
Cholecystokinin (CCK) is a peptide hormone and neurotransmitter that plays a crucial role in the gastrointestinal system, particularly in digestion and nutrient absorption. It is released by the enteroendocrine cells of the duodenum in response to the presence of fats and proteins.
**Why the Correct Answer is Right**
CCK has several functions, including:
* Stimulating the release of bile from the gallbladder into the bile duct and then into the small intestine, which helps in fat emulsification and absorption.
* Stimulating the release of pancreatic enzymes, such as amylase, lipase, and trypsin, which break down carbohydrates, fats, and proteins into smaller molecules.
* Causing contraction of the gallbladder to release bile.
* Stimulating the movement of food through the digestive tract.
* Acting as a neurotransmitter in the brain, where it is involved in the regulation of appetite and satiety.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely incorrect because it is not a well-known function of CCK.
**Option B:** This option is likely incorrect because CCK does not primarily stimulate the release of gastric acid.
**Option C:** This option is likely incorrect because CCK does not primarily stimulate the release of gastrin.
**Clinical Pearl / High-Yield Fact**
CCK is often used clinically to stimulate the release of digestive enzymes and bile, and is sometimes administered to patients with pancreatic insufficiency or cholestasis.
**Correct Answer:** D.