Peptide hormones: Pancreatic secretions – 1
The pancreas was first identified for western civilization by Herophilus (335–280 BC), a Greek anatomist and surgeon. Only a few hundred years later, Rufus of Ephesus, another Greek anatomist, gave the pancreas its name. The pancreas secrets three different peptide hormones. They are Insulin, Glucagon and Stomatostatin.
Anatomy of Pancreas:
- The pancreas (from pankreas: panG=all, kreasG=flesh); effering to the fleshy nature of the tissue) is both exocrine & endocrine gland.
- It locates the below the stomach between the curve of duodenum & spleen.
- It is a compact & lobulated organ.
- The pancreas composed of two types of cell.
- The pancreas secretes peptide hormones.
- Pancreatic hormones are peptide hormones
1. Glandular cells (or) Acinar (or) Acinii (exocrine):
The cells make up the bulk of the pancreatic tissues & secrete digestive juices into the duodenum by the pancreatic duct.
2. Polygonal cells (or) islets of langerhans (or) islet tissue (endocrine):
Its secretion releases into the blood directly. These were discovered by “Langerhans” in 1867. The islets of Langerhans in mammals contain three major types of cells, they are a-cells, b-cells, g-cells.
- alpha-cells –> Secretes – “Glucagon” hormones
- beta-cells –> Secretes – “Insulin” hormones
- gamma-cells –> Secretes-“Somatostatin” hormone
The pancreas secretes three different hormones, namely,
Peptide Hormone – Glucagon:
Chemistry of Glucagon:
First isolated in crystalline form by “Benhrens”& other.
This peptide hormone has a molecular weight of 3,485 and PI-8 and it has 29 amino acid residues.
“His” is the N-terminal amino acid and “Thr”, the C-terminal amino acid.
It contains no Cys, Pro, Ile, but Meth & Try are present in appreciable amounts.
Mechanism of Action:
Secretion of Glucagon:
Functions of Peptide hormone – Glucagon:
Glucagon stimulates glycogenolysis.
Glucagon acts through cAMP as its second messenger.
Glucagon stimulates gluconeogenesis by activation of pyruvate carboxylase.
Glucagon inhibits glucose oxidation by inhibiting pyruvate kinase.
It increases potassium release from liver.
In adipose tissue as well as in liver it increases the breakdown of lipids to fatty acids and glycerol.