The pancreas is a roughly pistol-shaped organ located deep in the upper abdomen, behind and below the stomach. It contains both endocrine and exocrine. The endocrine produce hormonal secretions that flow directly into the stream, and the exocrine produce secretions that flow into the intestinal tract.
The exocrine cells are arranged in rosette-shaped groups called acini around a small duct into which they secrete various enzymes essential for the breakdown of food in the process of digestion. These enzymes flow along the duct system, in response to the presence of food, into the small intestine where they assist the breakdown of food into small molecules that are then suitable for absorption through the wall of the intestine.
The endocrine cells are scattered among the exocrine acini in small clumps known as ‘islets of Langerhans’ named after their discoverer, the German pathologist Paul Langerhans. They contain two main types of cells: B cells, which secrete the vital hormone insulin, and A cells which secrete another hormone called glucagon, which has an opposite function.
Pancreas as a digestive organ
The liquid secreted by the pancreas in its exocrine role, known as pancreatic juice, is a clear watery fluid containing electrolytes (mostly sodium, potassium and bicarbonate ions) and 20 or more proteins. Nearly all the proteins are digestive enzymes. Secretion of pancreatic juice – between one and two litres per day -is stimulated by the presence of food in the stomach. The juice passes along the pancreatic duct into the duodenum, where some of the enzymes initiate the breakdown of proteins into peptides as a first step in their formation into amino acids. Another pancreatic enzyme, amylase, breaks down starch (carbohydrate) into various sugars, while the enzyme lipase acts with bile salts (from the gall bladder) to continue the digestion of fats.
Inflammation of the pancreas, particularly acute pancreatitis, is a serious condition which, if indicated, may lead to death. The principal symptoms are a sudden pain in the upper abdomen, often accompanied by vomiting, and shock. The patient may have a rapid pulse and cold, clammy skin. The cause cannot always be found, although alcoholism or obstruction of the bile duct by gallstones may be contributary factors. Injury to the pancreas – typically in a car accident – is another possible cause. Treatment usually involves the administration of pain killers and the emergency transfusion ofor plasma to counteract the effects of shock. Drugs to inhibit gastric and pancreatic secretions may also be given. Diabetes may be a secondary complication.
Insulin is one of the body’s most essentialbecause of its role in the metabolism of carbohydrates, fats and proteins. Its most important effect is to help to introduce glucose, the body’s prime source of energy, into practically all the body cells. Once in the cells, immediate use of it is made – to produce energy, except in the liver, where an excess of glucose is stored as a chemical called glycogen. In this form -as glycogen – glucose is available for use when needed in the short term. Other excess glucose is converted and stored as fat, a long-term source of energy. These functions are, of course, controlled by the amount of insulin secreted by the B cells. This in turn is regulated by the concentration of glucose in the blood. Immediately after a meal, the rise in blood glucose extracted and absorbed from food stimulates insulin secretion; this causes the storage of surplus glucose as glycogen in the liver, so that blood glucose level falls back to normal. Insulin secretion then decreases and glycogen is gradually converted back to glucose and released into the bloodstream until the next meal. Thus blood glucose is maintained fairly constant at an optimal level of about 90 mg of glucose per 100 ml of blood. This is equivalent to about 0.9 grams per litre of blood.
Insulin also increases the body’s fat and protein content by assisting in their formation from dietary sources and by inhibiting their breakdown in, in favour of carbohydrate utilization. When insulin secretion is low, for example during fasting or after destruction of B cells in diabetes, there is increased fat and protein breakdown, which results in weight loss.
Diabetes mellitus, often called sugar diabetes or simply diabetes, is a disorder that occurs when not enough insulin is secreted. In severe cases there is total, or near total, lack of insulin secretion so regular insulin administration – usually by injection – is essential for survival. This type of diabetes often, but not always, starts before the age of 30 years with an abrupt onset and requires urgent treatment with insulin. In the commoner and less severe type of diabetes, insulin deficiency is only partial, so treatment with insulin injections is not always needed. The onset of this type of diabetes is usually later in life and overweight people are particularly at risk. The condition may be controlled by a limited carbohydrate diet, and tablets that cause the pancreas to secrete more insulin. Often slimming helps the treatment of this condition. Because fewer kilograms of tissue are present, the total amount of insulin is relatively greater, and the shortage is less conspicuous. If insulin-secreting tablets are used or with insulin injections, sometimes there is too high a level of insulin in the blood and consequently a dangerously low drop in blood sugar can be the result. This is called hypoglycaemia.
Hypoglycaemia causes loss of concentration, drowsiness, sweating, hunger, palpitations and, if severe, loss of consciousness and convulsions. Sugar should be taken immediately to raise the blood glucose.
The main action of glucagon is to oppose and correct insulin-induced hypoglycaemia. It promotes the conversion of glycogen and proteins back into glucose and its secretion is stimulated by hypoglycaemia. When the level of glucose in the blood falls to an unacceptably low level, glucagon is secreted in the pancreas and this passes in the bloodstream to the liver. There it converts the glycogen into glucose. This in turn passes into the bloodstream to restore the level of glucose to what it should be.
Along with the other hormones adrenaline and Cortisol from the adrenal glands and growth hormone from the pituitary gland, glucagon acts as a safeguard against severe and prolonged hypoglycaemia. Glucagon injection is sometimes used to treat severe insulin-induced hypoglycaemia in diabetic patients.