In this article we will discuss about:- 1. Origin of Pancreas 2. Location and Structure of Pancreas 3. Hormones 4. Disorders.
Origin of Pancreas:
It is derived from the endoderm of the embryo.
Location and Structure of Pancreas:
The pancreas lies inferior to the stomach in a bend of the duodenum. It is both an exocrine and an endocrine gland. A large pancreatic duct runs through the gland, carrying enzymes and other exocrine digestive secretions from the pancreatic acinar cells to the small intestine.
The tissue of the pancreas has in addition to the acinar cells, groups of cells called islets of Langerhans, after the name of their discoverer (1869). These produce endocrine secretions.
Four kinds of cells have been identified in the islets:
(i) Alpha cells (about 15%) produce glucagon. Alpha cells are also called А-cells.
(ii) Beta cells (about 65%) produce insulin. Beta cells are also called В-cells.
(iii) Delta cells or D-cells (about 5%) produce somatostatin (SS), and
(iv) Pancreatic Polypeptide cells or PP cells or F-cells (15%), produce pancreatic polypeptide (PP). Beta cells are usually found towards the middle of the islet, the alpha cells towards the periphery of the islet and Delta (D) and F-cells are found scattered.
Hormones of Pancreas and Their Role:
(i) Glucagon:
It stimulates the liver to convert stored glycogen into glucose. Glucagon is also called an “anti-insulin” hormone.
Target Cells:
Glucagon acts on the cells of the liver and adipose tissue.
(ii) Insulin:
(a) It is antagonistic to glucagon. Insulin converts glucose into glycogen in the liver and muscles.
(b) It promotes protein synthesis in tissue from amino acids.
(c) Insulin reduces catabolism of proteins. It is an anabolic hormone.
(d) It increases the synthesis of fat in the adipose tissue from fatty acids.
(e) Insulin reduces the breakdown and oxidation of fat.
Target Cells:
Insulin acts on the cells of the liver muscles and adipose tissue. Alloxan and Cobalt chloride are compounds widely used by scientists to study cell physiology of islets of Langerhans. Alloxan is used to destroy the beta cells while cobalt chloride to destroy alpha cells of the islets of Langerhans.
(iii) Somatostatin (SS):
The same substance as growth inhibiting hormone from the hypothalamus, is produced not only by the pancreas and hypothalamus but also by some cells of the digestive tract. One of the actions of somatostatin seems to suppress the release of other hormones from the pancreas. It also appears to suppress the release of hormones from the digestive tract.
Target Cells:
Both somatostatin and pancreatic polypeptide act on the cells of the pancreas.
(iv) Pancreatic Polypeptide (PP):
It appears that pancreatic polypeptide inhibits the release of digestive secretion of the pancreas. Both somatostatin and pancreatic polypeptide are relatively newly discovered hormones of the pancreas, and both are still being studied.
Disorders of Pancreas:
(i) Diabetes mellitus (Hyperglycemia):
The most common endocrine disorder of the pancreas is the diabetes mellitus, now recognized to exist in two forms — insulin-dependent and non-insulin-dependent.
The insulin-dependent diabetes mellitus (IDDM) is caused by a failure of the Beta-cells to produce adequate amount of insulin while the non-insulin-dependent diabetes mellitus (NIDDM) appears to involve failure of insulin to facilitate the movement of glucose into cells.
In both disorders the blood glucose concentration is elevated above the normal range. Some of the glucose is excreted in the urine, and water follows the glucose, causing excessive urination and dehydration of body tissues. This causes excessive thirst (polydipsia). The cells are unable to utilize glucose and other carbohydrates for energy production.
They utilize their proteins for it. The person becomes very weak. Degradation of fats increases, producing ketone bodies (ketosis). The latter are acidic and poisonous. Blood cholesterol level rises. Healing power is impaired.
Administration of insulin lowers the blood-glucose level. It gives relief to the patient. A tendency towards non-insulin-dependent diabetes appears to be inherited as an autosomal recessive characteristic.
(ii) Hypoglycemia:
It occurs when the blood glucose level falls below normal. Theoretically, it may be caused by an excess of insulin, a deficiency of glucagon, or a failure of the secretion of the two hormones to completely regulate the blood sugar.
Some individuals have been found to have few or no Alpha cells and thus are deficient in glucagon, whereas others produce excess quantities of insulin usually because of a tumour of the beta cells.
The presence of excess insulin is more correctly referred to as hyperinsulinism. Symptoms of hypoglycemia include weakness, profuse sweating, irritability, confusion, unconsciousness and convulsions. It needs urgent intake of sugar or glucose.