**Question:** Peptide YY is secreted by

A. pancreatic endocrine cells
B. enteroendocrine L cells
C. central nervous system
D. gastrointestinal ECL cells

**Correct Answer:** B. enteroendocrine L cells

**Core Concept:** Peptide YY (PYY) is a peptide hormone that plays a role in regulating food intake, gastrointestinal motility, and glucose homeostasis. PYY is mainly produced by a subset of enteroendocrine L cells, which are scattered throughout the gastrointestinal tract, particularly in the colon and rectum.

**Why the Correct Answer is Right:** PYY is secreted in response to the presence of nutrients, particularly glucose, in the gastrointestinal tract. It acts on various target cells, including neurons in the central nervous system, to modulate food intake and gastrointestinal motility. PYY also has a role in glucose homeostasis, as it reduces glucose absorption in the gut and stimulates insulin secretion, which contributes to lowering blood glucose levels.

**Why Each Wrong Option is Incorrect:**

A. PYY is not secreted by pancreatic endocrine cells, which primarily produce insulin, glucagon, and other peptides involved in blood glucose regulation.

B. Although PYY is secreted by enteroendocrine L cells, the correct answer is "enteroendocrine L cells," not "enterohormones." Enteroendocrine cells are a broad term for cells that secrete hormones in response to the presence of nutrients in the gastrointestinal tract, and PYY is indeed one of them. However, the specific term for L cells is "enteroendocrine L cells," which clarifies the type of cells responsible for PYY secretion.

C. The central nervous system is involved in the processing of PYY signals, but it is not the site of PYY production. PYY is secreted by enteroendocrine L cells and acts on neurons in the central nervous system to modulate food intake and glucose homeostasis.

D. Gastrointestinal ECL cells are responsible for producing histamine, a different hormone involved in gastric acid secretion and gastrin release. PYY is secreted by enteroendocrine L cells, not ECL cells.

**Clinical Pearl:** Peptide YY is an essential hormone in the regulation of food intake, glucose homeostasis, and gastrointestinal motility. Understanding the correct source of PYY (enteroendocrine L cells) is crucial for appreciating its physiological role in gastrointestinal physiology and pathophysiology.