9th February 2024

Pancreas

Overview

The pancreas is responsible for both endocrine and exocrine functions. The islet of Langerhans contributes towards the endocrine function of the pancreas and consists of 3 main cell types:

Insulin

Insulin consists of an α chain and β chain linked by two disulphide bridges. It is synthesised from proinsulin within the β-cells. Hydrolysis of the C-peptide molecule from proinsulin produces the active insulin molecule. 

Its secretion is stimulated by glucose, fatty acids, parasympathetic response, gut hormones (e.g., gastrin, secretin, CCK, glucagon) and certain drugs (e.g., β agonists, sulphonylureas). Sympathetic response, β-blockers, dopamine and somatostatin inhibit its secretion.

It aids in reducing the serum concentration of glucose by stimulating glucose uptake by cells. This increases glycogen and lipid production within the liver while reducing gluconeogenesis and ketogenesis. Adipose tissues will increase their fatty acid synthesis and lipid storage. Muscles will increase their synthesis of glycogen and proteins and increase amino acid uptake. It is worth noting that insulin has no effect on glucose transport in the brain, kidneys, intestine and red blood cells.

The primary condition that involves insulin is diabetes mellitus ( both type 1 and type 2). Type 2 diabetes mellitus is caused by insulin resistance, which can be associated with several conditions, including obesity, pregnancy, polycystic ovarian syndrome, cystic fibrosis and acromegaly. 

Glucagon

Glucagon is a polypeptide that increases blood glucose concentrations by increasing glycogenolysis, gluconeogenesis and lipolysis. It also stimulates urea production. Its secretion is stimulated by decreasing blood glucose levels. 

Somatostatin

Somatostatin is a polypeptide hormone produced by the pancreas and the neurons within the hypothalamus. It suppresses the endocrine and exocrine functions of the pancreas. Along the rest of the digestive tract, it inhibits the secretion of other GI hormones, reducing gastric emptying and smooth muscle contractions. In the CNS, it inhibits the release of prolactin, GNRH and TSH. 

References

Tortora, G. J., & Derrickson, B. (2017). Tortora’s principles of anatomy and physiology. John Wiley and Sons.

Kumar, P. and Clark, M., (2012). Kumar & Clark’s clinical medicine. 8th ed.