**Question:** Peptide YY is secreted by

A. Enterochromaffin cells in the gastrointestinal tract
B. Pancreatic beta cells
C. Neurons in the hypothalamus
D. Neurons in the spinal cord

**Correct Answer:** Peptide YY (PYY) is secreted by **Enterochromaffin cells in the gastrointestinal tract**.

**Core Concept:** Peptide YY is a peptide hormone that plays a role in regulating energy homeostasis, satiety, and glucose homeostasis. It is secreted in response to meal ingestion and acts on Y1 and Y2 receptors in the brain to modulate feeding behavior and glucose homeostasis. PYY acts to reduce food intake, delay gastric emptying, and stimulate insulin secretion.

**Why the Correct Answer is Right:** Enterochromaffin cells are specialized cells found in the gastrointestinal tract, particularly in the distal small intestine and colon. These cells are known for producing and releasing the serotonin precursor, 5-hydroxytryptophan (5-HTP), into the bloodstream. PYY is one of the substances secreted by enterochromaffin cells in response to the presence of food, specifically the ingestion of carbohydrates and proteins. PYY acts as an inhibitory signal to the hypothalamus, leading to a decrease in hunger and food intake.

**Why Each Wrong Option is Incorrect:**

**A.** Enterochromaffin cells in the gastrointestinal tract also secrete other substances like serotonin and 5-HTP, but not PYY.

**B.** PYY is not secreted by pancreatic beta cells, which are responsible for insulin secretion and are part of the islets of Langerhans in the pancreas.

**C.** Neurons in the hypothalamus are involved in the regulation of feeding behavior and energy homeostasis, but they are not the site of PYY secretion.

**D.** PYY is not secreted by neurons in the spinal cord, which are responsible for transmitting sensory information about pain and touch, not regulating satiety and food intake.

**Clinical Pearls:**

**1. PYY and satiety:** PYY plays a crucial role in signaling satiety and regulating food intake. This hormone contributes to the overall control of energy homeostasis in the body.

**2. PYY and glucose homeostasis:** PYY, along with other gastrointestinal hormones like GLP-1, contributes to the regulation of glucose homeostasis by slowing gastric emptying, enhancing insulin secretion, and reducing glucagon secretion. This helps maintain stable blood glucose levels and prevents postprandial hyperglycemia.

**3. PYY and its role in diabetes:** In patients with type 2 diabetes, a decrease in PYY secretion or its sensitivity can lead to increased food intake and reduced satiety, contributing to weight gain and worsening of diabetes symptoms. Restoring PYY levels or sensitivity has been shown to improve glucose homeostasis and reduce body weight in animal models of diabetes.

In conclusion, PYY is primarily secreted by enteropause cells in the gastrointestinal tract in response to nutrient ingestion