Overview
The endocrine pancreas controls blood glucose mainly through insulin from β cells, glucagon from α cells and somatostatin from δ cells. This topic covers their synthesis, secretion, signaling pathways and effects.
The endocrine pancreas and glucose transport
The endocrine pancreas plays a critical role in glucose homeostasis, maintaining near-constant blood glucose levels unlike other sugars like lactose and galactose. It achieves this through the secretion of key hormones: insulin from β-cells and glucagon from α-cells. These hormones, along with others like epinephrine and cortisol from the adrenal glands, work in concert to regulate blood glucose.
The endocrine portion of the pancreas is composed of clusters of cells called the islets of Langerhans, which constitute only about 1% of the total pancreatic mass. These islets contain four main cell types, each responsible for secreting a specific hormone:
- β cells: Secrete insulin, the most abundant hormone of the islet.
- α cells: Secrete glucagon.
- δ cells: Secrete somatostatin, which has a modulatory role on other islet cell secretions.
- Other cells: Secrete pancreatic polypeptide and other less understood peptides.
Glucose is transported into the cells via 2 mechanisms,
- ♦ Co-transport with Na+.
- ♦ Facilitated diffusion via GLUT, there are 5 types of GLUT:
- GLUT 1, is found in many tissues, e.g. erythrocytes, muscles, brain, kidney, colon, placenta etc.
- GLUT 2, is found in liver, pancreatic β-cells.
- GLUT 3, is found in the brain.
- GLUT 4, is found in skeletal muscle, adipose tissue.
- GLUT 5, is found in small intestine (* fructose transporter)