What are the major functions of “I” cells?
**Core Concept:** "I" cells, also known as Islets of Langerhans, are specialized cell clusters found in the pancreas. They consist of 5 types of cells: alpha, beta, delta, gamma, and PP cells. Each cell type has specific functions and roles in maintaining glucose homeostasis and hormonal regulation.
**Why the Correct Answer is Right:** The major functions of alpha cells are related to glucagon secretion, which helps control blood glucose levels by stimulating glycogen breakdown in the liver, leading to increased glucose output into the bloodstream. This helps lower blood glucose levels during hypoglycemia.
**Why Each Wrong Option is Incorrect:**
A. Beta cells primarily secrete insulin, which lowers blood glucose levels by promoting glucose uptake by target cells (e.g., muscle, adipose, and liver cells), glycogen synthesis in the liver, and inhibition of gluconeogenesis and glycogenolysis. Beta cells are not primarily responsible for glucagon secretion.
B. Delta cells are involved in the secretion of somatostatin, an inhibitory hormone that modulates the secretion of other pancreatic hormones (e.g., inhibiting insulin and glucagon release from B cells, and pancreatic polypeptide secretion from PP cells).
C. Gamma cells secrete pancreatic polypeptide (PP), which modulates the secretion of other pancreatic hormones (e.g., stimulating glucagon release from alpha cells and inhibiting insulin release from beta cells).
D. PP cells, also known as PP cells, secrete pancreatic polypeptide (PP), which modulates the secretion of other pancreatic hormones (e.g., stimulating glucagon release from alpha cells and inhibiting insulin release from beta cells).
**Clinical Pearl:** Understanding the various functions of "I" cells and their interactions is crucial for maintaining glucose homeostasis and preventing hypo- and hyperglycemia.
**Correct Answer:** D. Pancreatic polypeptide (PP) cells, also known as PP cells, secrete pancreatic polypeptide (PP), which modulates the secretion of other pancreatic hormones (e.g., stimulating glucagon release from alpha cells and inhibiting insulin release from beta cells).