Structure and function of Pancreatic islets
Structure of Pancreatic islets:
In the human body, there is an organ called the pancreas, located at the bottom of the stomach and next to the duodenum. Its main function is to secrete many digestive enzymes. In addition to the organization that secretes digestive enzymes, there are also many scattered cells in the pancreas, like islands in the ocean, so they are called Pancreatic islets. As early as 1869, Langerhans discovered these cell clusters in the pancreas and they were also called Langerhans islands. There are 250,000 to 500,000 Pancreatic islets in a mature pancreas, accounting for 1% to 2% of the pancreas volume and weighing about 1 gram.
Pancreatic Islet size varies greatly, with small Pancreatic islets containing only a few cells and large Pancreatic islets containing over 5,000 cells, with a diameter of less than 40 microns. With age, Pancreatic islet cell quantity gradually decreases, with the newborn period accounting for 20%, children (1.5 years old to 11 years old) accounting for 7.5%, and adults accounting for only about 1%.
Function of the Pancreatic islets:
Modern medicine has found that the islet is composed of various cells, mainly four types: α cells, β cells, δ cells, and pp cells. Among them, insulin secreted by β cells is the main hormone regulating carbohydrate metabolism. Cells secrete glucagon, δ cells secrete gastrin and somatostatin, and pp cells secrete pancreatic polypeptide, all of which have many important physiological functions.
Physiological functions of Pancreatic islet hormone
Physiological function of insulin:
The secretion of insulin in normal people has a certain rule. About 50U is secreted every day, accounting for 1/5 of the total pancreatic insulin storage. In the basic state, 0.5~1.0u can be secreted every hour. Insulin secretion can increase 5-10 times after a meal. This is because the blood glucose increases after a meal, which increases the glucose concentration around the tissues in the body. When the blood glucose exceeds the fasting level, the insulin secretion of pancreatic islets β Cell stimulation was enhanced and insulin secretion rapidly increased. The higher the blood glucose, the more insulin secretion.
Generally, after eating carbohydrate food for 1 hour, blood glucose reaches the peak and insulin level also reaches the peak. Three hours after a meal, blood glucose and insulin levels fell to fasting basal levels. The regulation between blood glucose and insulin is automatic and sensitive. Once the regulation of insulin is abnormal, diabetes or other diseases will occur.
Glucose usually exists in the body fluid around tissue cells. Wells cannot directly enter cells. Only under the action of insulin can it enter cells and then be used. Each cell is like a small stove, and glucose is equivalent to firewood or coal, Through “combustion”, energy is generated to supply the body for use. In this process, insulin is equivalent to a key, which opens the door for glucose to enter the cell and transports glucose into the cell. That is to say, without insulin, the human body cannot make full use of glucose. On the other hand, insulin can store glucose in the human body, just like transporting glucose to a warehouse.
For example, in the liver, insulin converts glucose into liver glycogen, so that 60% – 70% of the glucose flowing through the liver is stored in liver cells in the form of liver glycogen, and it can also convert glucose into muscle glycogen in muscle and fat cells for storage. Once the blood glucose in the body is lower than normal, these “warehouses” are in addition, insulin can also inhibit hepatic glycogenolysis, prevent gluconeogenesis, reduce glucose production in the liver, and further stabilize blood glucose levels.
In addition to the above physiological functions, insulin is also involved in regulating protein and fat metabolism. It can inhibit protein breakdown, promote protein synthesis, and also inhibit lipolysis. During fasting, due to the low level of plasma insulin, nutrients in the body change from synthesis to decomposition, and fatty acid production increases. The main role of low-level insulin is to prevent ketosis or ketoacidosis.
The physiological function of glucagon
which can inhibit β Cells secrete insulin and promote δ Cells secrete somatostatin. Its main physiological functions are to promote liver glycogenolysis, xenogenesis, lipolysis and ketone body production, and cooperate with insulin to maintain normal blood glucose levels.
