Cholecystokinin is

Options

A. Bile pigment
B. Enzyme
C. Lipid
D. Gastrointestinal hormone.

Answer

**Step-by-Step Solution:**

1. **Understanding Cholecystokinin (CCK)**: Cholecystokinin, commonly referred to as CCK, is a hormone involved in the digestive process. It was previously known as Pancreozymine.

2. **Function of CCK**: CCK plays a crucial role in digestion by stimulating the gallbladder to contract and release bile into the duodenum. It also stimulates the pancreas to release digestive enzymes.

3. **Stimulus for CCK Release**: The secretion of CCK is triggered by the presence of hydrochloric acid (HCl), amino acids, and fatty acids in the duodenum, which occurs when food moves from the stomach into the small intestine.

4. **Role in Digestion**: CCK not only helps in the digestion of fats and proteins by promoting enzyme secretion from the pancreas but also aids in the emulsification of fats by releasing bile from the gallbladder.

5. **Additional Functions**: Besides its digestive functions, CCK also induces a feeling of fullness (satiety) and inhibits gastric emptying, which helps regulate the pace of digestion.

6. **Classification of CCK**: Given its functions related to digestion and its secretion from the gastrointestinal tract, CCK is classified as a gastrointestinal hormone.

7. **Conclusion**: Based on the functions and characteristics discussed, the correct answer to the question "Cholecystokinin is" is that it is a gastrointestinal hormone.

**Final Answer**: Cholecystokinin is a gastrointestinal hormone.

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