pancreas hormones

Pancreas / Pancreatic Islets

Structure of pancreas, scattered acinar cells are 1-2 million tiny clusters of endocrine tissue called pancreatic islets or islets of Langerhans that produce pancreatic hormone.

There are no duct leading from clusters of islet cells. 

Pancreatic hormones are secreted directly into bloodstream and circulate throughout body.

In pancreas 99% are acinar cells, forming bulk of gland. Acinar cells, arranged in clusters, produce digestive enzyme rich juice that is ducted into small intestine during food digestion.

Types of Cell

1. Alpha cells

Constitute 17% of islets of Langerhans. These cells secretes glucagon.

2. Beta cell

Cells constitute about 70% of islets of Langerhans. These cells secrete insulin hormone.

3. Delta cells 

Constitute 7% of islets of Langerhans. These cell secretes somatostatin.

4. F cells 

Secrete pancreatic polypeptide.

Normal blood glucose level is between 63 to 144mg/100ml.

Blood glucose levels are controlled mainly by opposing actions of insulin and glucagon.

1. Glucagon increases blood glucose levels.

2. Insulin reduced blood glucose levels.

Hormones of pancreas

1. Insulin 

2. Glucagon

3. Somatostatin 

1. Insulin

Insulin is polypeptide consisting of about 50 amino acids.

It's main function is to lower raised blood nutrient levels, not only glucose but also amino acids and fatty acids.

Circulating insulin lowers blood glucose levels by the following actions;

The uptake of glucose by cells decreases blood glucose and increases availability of glucose for cellular reaction in which glucose participates.

Acting on cell membranes and stimulating uptake and use of glucose by muscle and connective tissue cells.

Increasing conversion of glucose to glycogen (glycogenesis), especially in liver and skeletal muscles.

Insulin inhibits glycogenolysis (breakdown of glycogen to glucose) and Gluconeogenesis (conversion of amino acid or fats to glucose).

It increases uptake of amino acids and increase protein synthesis in muscle tissue.

Promoting synthesis of fatty acids and storage of fats in adipose tissue (lipogenesis).

Regulation of insulin secretion

Secretion of insulin is stimulated by increased blood glucose level but rising plasma level of amino acids and fatty acids and release of acetylcholine by parasympathetic nerve fiber also trigger insulin release.

2. Glucagon 

Effects of glucagon increase blood glucose level.

One molecules of this hormone can cause release of 100 million molecules of glucose into blood.

The major target of glucagon is liver, where following function occurs;

1. Breakdown of glucogen to glucose (glycogenolysis) in liver and skeletal muscles.

2. Synthesis of glucose from lactic acid.

3. Release of glucose to blood by liver cells, which causes blood glucose levels to rise.

Secretion of glucagon is stimulated by low blood glucose level, exercise and decreases by somatostatin and insulin.

3. Somatostatin (GHRIH)

The effect of this hormone, also produced by hypothalamus, is to inhibit secretion of both insulin and glucagon in addition to inhibiting the secretion of GH from anterior pituitary.

4. Pancreatic polypeptide

It inhibits somatostatin secretion, gall bladder contraction and secretion of digestive enzymes by pancreas.