Origin and Structure
(Image Courtesy: www.wikipedia.com)
Pancreas is derived from the endoderm of embryo. The pancreas is a mixed gland found between the stomach and duodenum. The pancreas consists of the groups of cell mass. These cells are involved in the secretion of digestive enzymes. Such cell masses constitute about 90% of the pancreas. The endocrine part of the pancreas consists of clusters of cells known as islets of Langerhans (reported by Langerhans in 1869) which constitute remaining 10% part of the organ. Three types of cell are identified in islets of Langerhans:
Hormones of Pancreas The islets of Langerhans produce the following three hormones :
Now I will explain these three hormones in detail.
Insulin Insulin is secreted by the beta cells of islets of Langerhans. Insulin was extracted by two Canadian scientists Banting and best in 1922. Insulin is protein hormone which contains 51 amino acid residues arranged in two chains. Recent studies have shown that insulin is synthesized in the beta cells as proinsulin. Proinsulin is biologically inactive and is present in very small quantity about 5% of total insulin content in the pancreas.
Function of Insulin The main function of Insulin is to regulate the amount of glucose in the blood by converting the excess of glucose into glycogen. The process of converting glucose into glycogen is called glycogenesis. This glycogen is stored in the liver and muscles.
Hyposecretion of Insulin Deficiency of Insulin, results in excess glucose in the blood, so much, so that it starts appearing in the urine. This disease is known as diabetes mellitus. Complete lack of insulin in the body may result in diabetes mellitus, a disease characterized by the following symptoms:
Hypersecretion of Insulin Hypersecretion of Insulin results in hypoglycemia. In this condition, the brain becomes more active or sensitive. The person is excessively tired due to the low glucose level in his blood. Intelligence and reproductive ability are also affected. Such symptoms may also arise if insulin is administered orally or intravenously in a person doing excess labour and exercise or in case of hunger and fast. This situation is known as insulin shock.
Glucagon Glucagon is secreted by the alpha cells of islets of Langerhans. Glucagon is a single chain of the polypeptide containing 29 amino acid residues. This hormone is secreted in response to hypoglycemia. Glucagon was discovered by Kimball and Martin in 1923.
Function of Glucagon The effect of glucagon is just opposite to that of insulin. Glucagon stimulates glycogenolysis, gluconeogenesis and glucose releases by the liver. Glucagon is also an important regulator of amino acid metabolism, lower level of calcium in the blood, higher excretory level of calcium, an increase in heartbeat and increase in the force of cardiac contraction.
Somatostatin Somatostatin is newly discovered hormone secreted by the pancreas. Somatostatin is the polypeptide and increases the duration of assimilation of digested food. Due to such an effect, the utility of food materials is maintained for a longer period. The hormone is secreted by gamma cells of the islets of Langerhans.
Regulation of Pancreas The secretion of the islet cells is directly controlled by the level of blood sugar via the negative feedback mechanism. When the blood sugar level falls below normal, alpha cells are stimulated to secreted glucagon but are no longer stimulated when the level of sugar rises. On the other hand, increased level of glucose in the blood stimulates the beta cells to secrete insulin while the lower concentration of the sugar does not stimulate beta cells. It is a self-regulating device.
Last words So, the pancreas is a mixed gland which performs both exocrine and endocrine functions. The exocrine part of pancreas produces digestive juice and helps in digestion while the endocrine part produces different hormones.
Hakimuddin Kuwakhedawala is based in India with over 15 years experience as a teacher. Teaching and writing are his passion. Most of the articles of Hakimuddin are related to education, exam, environmental problems, etc.
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A small correction, it is the delta cells of the pancreas that secrete Somatostatin and not the gamma cells. The gamma cells secrete pancreatic polypeptide.
The pancreatic digestive enzymes (exocrine part secretions) are available for treatment of chronic pancreatitis wherein people have difficulty to digest food. The pancreas is a gland that can be damaged by alcohol consumption leading to acute pancreatitis that can be life-threatening.