Pancreas is an organ with both exocrine and endocrine functions that plays a crucial role in glucose homeostasis.¹ It is known to be composed of five different endocrine cell types that produce different types of hormones. The hormones insulin and glucagon – major players in glucose homeostasis – are produced by the beta and alpha cells of the pancreas, respectively.

Insulin

Insulin is a hormone produced by the pancreatic beta cells.¹ It is a peptide hormone, meaning it is made up of strings of amino acids. It is first produced as proinsulin and then becomes insulin that acts on the body when a part of the proinsulin (i.e., C-peptide) gets cut off. Although C-peptide has no biological action, it is often used to measure the level of insulin secretion. 

Insulin is secreted by the pancreas when blood glucose levels rise after a meal.² This signals the cells in the body to take up and use glucose and for excess glucose to be stored in the liver as glycogen molecules, ultimately lowering blood glucose levels. It primarily targets liver, muscle, and adipose (i.e., fat) tissues.

Glucagon

Glucagon is a hormone produced by the pancreatic alpha cells.¹ It is first produced as a preproglucagon, which then ultimately becomes secreted as glucagon after several enzymatic processes.

Glucagon is secreted by the pancreas when blood glucose levels fall.² One of its primary actions is on the liver, where it signals the stored glycogen molecules to be broken down and made into readily available glucose molecules through a process called glycogenolysis. It also promotes the body to synthesize new glucose molecules through a process called gluconeogenesis to provide the needed energy supply. This, in effect, raises blood glucose levels. 

Through opposing yet stabilizing actions of these two primary hormones, the body keeps glucose levels in a tight range, allowing physiological functions to run smoothly.