Islets of Langerhans: Structure, Function & Diseases

The islets of Langerhans are a collection of cells located in the pancreas. They produce insulin, secrete it, and regulate the level of blood sugar.

What are the islets of Langerhans?

The pancreas is made up of a wide variety of cell types. Between the glandular tissue, there are about a million of cell clusters arranged in an island shape called the islets of Langerhans. They were named after the physician Paul Langerhans and have the task of regulating blood glucose levels via the hormones glucagon and insulin.

Anatomy and structure

The islets of Langerhans are collections of cells consisting of about 2000 to 3000 cells. The islets account for about one to three percent of the mass of pancreatic tissue and are more abundant in the tail region than in the head region. A distinction is made between a total of four endocrine islet cell types: B cells are responsible for the production of insulin. They can be selectively visualized by immunohistochemistry and contain very typical secretory granules in the electron microscope as well as a crystalline center. Glucagon is produced by the A cells, which are located in the outer region of the islets. They are larger than the B cells and make up about twenty percent of the islet cells. If the glucose concentration in the blood drops, the A cells release glucagon. This increases glucose release or glucose synthesis, and the blood glucose concentration increases. The D cells produce somatostatin, which inhibits the secretion of glucagon and insulin. The fourth group is the PP cells, which form pancreatic polypeptiol, inhibiting pancreatic secretion. An islet is supplied by one to three islet arterioles each. These may split into capillaries in the outer part of the islet or in the center. Thus, the islets are supplied from the depth or from the surface. There are also several draining vessels through which blood leaves the islets. These are called insuloacinar portal vessels and open into the exocrine acinar cells.

Function and Tasks

Glucagon and insulin are produced in the islets of Langerhans, both of which are important for carbohydrate metabolism. Insulin is used to lower blood glucose levels. If carbohydrates are ingested, insulin is secreted, which promotes the utilization or absorption of glucose. When insulin is produced, proinsulin splits into a C-peptide and an insulin molecule, both of which are secreted in the same ratio. This makes it possible to determine whether the body’s own insulin is still being produced. Insulin also influences the appetite and prevents fat tissue from being broken down. If insulin is insufficiently effective, very high triglyceride levels can be detected. If there is a complete lack of insulin, the body is flooded with fatty acids and severe metabolic disorders occur. The counterpart to insulin is glucagon. Glucagon promotes glycogen breakdown in the liver and stimulates insulin secretion. If the blood glucose level drops or if a person eats a meal very rich in protein, glucagon is released. Glucose is then released in the liver, causing the blood glucose level to rise again. This reciprocal glucagon and insulin synthesis causes blood glucose levels to normalize very quickly.

Diseases

A very common disease is diabetes mellitus (diabetes). Diabetes is characterized by elevated blood glucose levels and sugar in the urine. Patients also complain of severe thirst, blurred vision, itching, skin infections, and weight loss. High blood sugar levels cause damage to blood vessels, and cholesterol and fats are deposited, increasing the risk of heart attack. In the eye, deterioration to blindness occurs and the kidney may fail completely. In addition, the nerves in the feet and legs can also be damaged, so that minor injuries are often not noticed. If the wounds become infected, ulcers develop, leading to a condition known as diabetic foot. In type 1 diabetics, very little or no insulin is secreted because the B cells have been destroyed by the immune system. In type 2 diabetics, the body cannot respond sufficiently to the insulin released and insulin production decreases.This type is also called “adult-onset diabetes” because it usually does not occur until the age of about 56, but it can also develop in overweight people or in people with elevated blood lipids. Another form of diabetes can also occur during pregnancy due to an insensitivity to insulin, which is hormonal. As a result, abnormal glucose tolerance occurs, but disappears after pregnancy. Secondary diabetes develops as a result of other diseases, for example due to diseases of the pancreas, hyperthyroidism, infections or long-term medication. Insulin secretion can be restored by transplanting isolated islet cells. To do this, islet cells are first isolated from the pancreas of a donor and purified in a very complex procedure. The cells are then transplanted into the liver via a catheter, where they resume the regulation of blood glucose. Immunosuppression (suppression of the body’s defenses with drugs) is necessary to prevent the foreign tissue from being rejected. Many diabetics can thus do without injected insulin, but the duration of success has been relatively limited so far. Many transplanted patients require insulin again after about a year, so islet cell transplantation is still not a routine procedure in diabetology.

Typical and common diseases of the pancreas.