Origin. The pancreas develops from the endoderm of the embryo.
Pancreas Location. The pancreas lies below the stomach.
Pancreas Structure. The pancreas is an elongated, yellowish gland. It consists largely of lobules (acini, alveoli) that secrete pancreatic juice. Interspersed at random among the acini are islands of Langerhans which produce hormones. The islands of Lan-gerhans consist of four types of cells : fewer larger alpha cells, numerous beta cells , delta cells and F cells.
The islands of Langerhans secrete four hormones : insulin, glucagon, somatostatin and pancreatic polypeptide.
(i) Insulin. It is secreted by the beta cells on “stimulation by a rise in blood-glucose level, such as after a meal. Insulin serves many functions.
(a) It enables the liver and muscles to store glucose as glycogen (glycogenesis) and enables the tissues to take up and use glucose as a source of energy . This lowers the blood-glucose level.
(b) It promotes synthesis of proteins from amino acids in the tissues.
(c) It reduces breakdown of proteins to maintain the tissues.
(d) It promotes synthesis of fats from fatty acids and glucose in the adipose tissue.
(e) It reduces respiratory breakdown of fats in the body.
Insulin is an anabolic hormone.
Deficiency Disorder of insulin
Deficiency of insulin causes diabetes mellitus. The patient cannot use or store glucose. Thus, glucose, accumulates in the blood from where it is excreted by kidneys in urine. Glucose increases osmotic pressure of urine, causing loss of water from the body in urine. This produces excessive thirst. Degradation of fats increases, producing ketone bodies such as acetoacetate and acetone. Blood cholesterol rises. Breakdown of proteins also increases, leading to wasting of body tissues. Healing power is impaired. Injuries may change into gangrenes*. The diabetic person has blurred vision, and is weak, tired, irritable, nauseated, and underweight. In extreme cases, patient may pass into coma (complete loss of consciousness) and die. Administration of insulin gives relief by lowering blood-glucose level. Diabetes caused by insufficient insulin production is called insulin-dependent diabetes.
Diabetes mellitus may also be caused by failure of insulin to move glucose from the blood into the cells for storage or consumption. This may be due to defective insulin receptors on cell surfaces, starving the cells of glucose; or to an abnormality in a recently discovered pancreatic protein amylin, which is thought to regulate insulin’s activity. Diabetes due to person’s inability to use insulin is termed insulin- independent diabetes. It is more common than insulin-dependent diabetes.
(ii) Glucagon. It is secreted by the alpha cells of the islands of Langerhans in response to a fall in the blood glucose level. Its action is opposite to that of insulin. It brings about change of liver glycogen to blood glucose (glycogenolysis). It also forms glucose from amino glucose from acids and fats (gluconeogenesis). Both the processes increase blood-glucose level to provide energy between meals. It is, therefore, also known as hyperglycemic hormone. Excess of glucose in the blood suppresses the secretion of glucagon whereas fall in glucose level starts glucagon production.
(iii) Somatostatin (SS). It is secreted by the delta cells. This hormone decreases the rate of nutrient absorption into the blood stream from the gastrointestinal tract. It also inhibits the secretion of hypophysial growth hormone. It is an inhibitor of both insulin and glucagon too.
(iv) Pancreatic Polypeplide. It is secreted by the F cells. It inhibits the release of pancreatic juice.
Differences between Diabetes Mellitus and Diabetes Insipidus
1. It is caused by deficiency of insulin.
2. It is, thus, a pancreatic diaorder.
3. Blood sugar rises and glucose is excreted in urine.
4. Blood chloesterol increases and ketone bodies appear in urine.
1. It is caused by deficiency of antidiuretic hormone (ADH).
2. It is, thus, a hypothalamic disorder.
3. Blood sugar remains normal and glucose is not lost in urine.
4. These symptoms are lacking.