The endocrine part of the pancreas is dispersed inpancreasIrregular clusters of cells in.There are at least three types of cells in the islet: A (or a2) cells secrete glucagon;B (or β) cells secrete insulin;Recently, another kind of cell, called D (or δ or α 1) cell, is found, which normally secretes growth hormone releasing inhibitory hormone.When D cells proliferate or tumors occur, they secrete a large amount of gastrin, which is called gastrinoma.Peptic ulcer that can cause excessive gastric acid secretion.The islets of langerhans are close to the capillaries, and the hormones secreted by these cells penetrate into the blood through the capillary wall, which has the function of regulating glucose metabolism.
1. Pancreatic islets are endocrine cell clusters distributed among the acini in the exocrine part of the pancreas, which are distributed unevenly in all parts of the pancreas, with the tail of the pancreas being the most.Pancreatic islets vary in size, with only a few cells for small ones and hundreds for large ones.In addition, there are scattered endocrine cells near the acini and ducts.People have about 500000 islets, accounting for 1-2% of the pancreas volume.The islets are homologous with the exocrine portion of the pancreas, and arise from the dorsal and abdominal pancreatic buds protruding from the endoderm at the end of the foregut.Most of the epithelial cells in the two pancreatic buds form exocrine parts;Some cells are scattered in the exocrine part to form islets.In recent years, it has been proposed that islets originate from neural crest cells transplanted into the pancreatic primordium early in the embryo, but there is still controversy.
2. Pancreatic islets are covered by a membrane composed of thin reticular fibers, but the membrane is not complete.The cells of the islets are arranged into cords, and the capillaries between the cords are abundant.The cells are smaller than acinar cells, polygonal and round in shape, different in size, and lightly stained in cytoplasm.The nucleus is round, located in the center of the cell, and the chromatin particles are dense.With special staining method, B cells, A cells and D cells can be distinguished in humans and some animals.PP cells and D1 cells were also found by electron microscopy and immunohistochemistry.In addition to C cells, other cells are known to secrete peptide hormones, and a series of scholars have listed them in the APUD cell system and in the gastrointestinal pancreatic endocrine system.Their organelles are underdeveloped, and their main feature is that they have secretory granules.The shape and structure of various cell secretory granules have their own characteristics.
3. There are abundant porous capillaries in the islets of langerhans.In recent years, it has been found that the artery entering the pancreas first goes to the islet and divides into capillaries, then converges into veins and divides into capillaries between the acini in the exocrine part, forming the islet acinar portal system.The blood flow from the islet to the acinus contains high concentrations of insulin and glucagon, which regulate the exocrine activity of the pancreas.There are cholinergic and adrenergic nerve endings in the islets of langerhans. The former may promote the secretion of B cells, while the latter promotes the secretion of A cells.
4、islet cellsIts secretion is regulated by blood glucose levels, gastrointestinal hormones and nerves.When the blood sugar level is high, it stimulates B cells to secrete insulin, and when the blood sugar level is low, it stimulates A cells to secrete glucagon.Enterotropin, glucagon and gastric inhibitory polypeptide promote B cell secretion.Growth hormone release inhibiting hormone inhibits the secretion of B and A cells.At ordinary times, the vagus nerve stimulates B and A cells to secrete a small amount of hormone to keep blood sugar at a normal level;When sympathetic nerve is excited, it can inhibit B cells, promote A cells and increase blood sugar content.
Main functions of insulin
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insulinIt mainly acts on liver, muscle and adipose tissue, controlling the metabolism and storage of protein, sugar and fat.
(1) Effect on sugar metabolism.It can accelerate the utilization of glucose and inhibit the production of glucose. Even if the destination of blood sugar increases and the source decreases, the blood sugar decreases.
① AccelerationglucoseUtilization of.Insulin can improve the permeability of cell membrane to glucose, promote the transport of glucose from outside the cell to inside the cell, provide favorable conditions for the tissue to use sugar, promote the activity of glucokinase (inside the liver) and hexokinase (outside the liver), promote the conversion of glucose to glucose 6-phosphate, and thus accelerate the fermentation and oxidation of glucose;It also promotes the synthesis and storage of liver glycogen and muscle glycogen under the action of glycogen synthase.
② Inhibiting the production of glucose can inhibit the decomposition of liver glycogen into glucose, and inhibit the conversion of glycerol, lactic acid and amino acid into glycogen, reducing the heterogenesis of glycogen.
(2) Effects on fat metabolism.Promote fat synthesis and storage, and inhibit fat decomposition.In diabetes, glucose metabolism is impaired, fat is mobilized in large quantities, and a large number of free fatty acids are produced, which are oxidized to acetyl coenzyme A in the liver, and then become ketone bodies. If too many ketone bodies are produced, ketosis will occur.Insulin can inhibit fat decomposition and promote the utilization of sugar, thus inhibiting the production of ketone body and correcting ketosis.
(3) Effect on protein metabolism.Promote protein synthesis and prevent protein decomposition.
(4) Insulin can promote potassium and magnesium ions to pass through the cell membrane and enter the cell;It can promote the synthesis of deoxyribonucleic acid (DNA), ribonucleic acid (RNA) and adenosine triphosphate (ATP).
In addition, the entrance and exit of glucose in red blood cells and brain cell membranes, the reabsorption of glucose in renal tubules and the absorption of glucose by intestinal mucosal epithelial cells are not affected by insulin.The target cells of insulin mainly include liver cells, fat cells, muscle cells, blood cells, lung and kidney cells, testicular cells, etc.
Insulin related indications
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1. Patients with insulin analogue type 1 diabetes mellitus, due to their impaired islet beta cell function and absolute insufficient insulin secretion, need insulin treatment at the onset of disease, and need lifelong insulin replacement therapy to maintain life and life.It accounts for about 5% of the total number of diabetics.On the basis of lifestyle and combined treatment of oral hypoglycemic drugs, patients with type 2 diabetes can start combined treatment of oral drugs and insulin if their blood sugar still fails to reach the control goal.Generally, when HbA1c is still greater than 7.0% after a large dose of multiple oral drugs combined treatment, insulin treatment can be considered.Emaciated diabetic patients with new onset and difficult differentiation from type 1 diabetes.In the course of diabetes (including newly diagnosed type 2 diabetic patients), when there is no obvious cause of weight loss, insulin treatment should be used as early as possible.For patients with newly diagnosed type 2 diabetes mellitus with high blood sugar, it is difficult to control blood sugar satisfactorily with oral drugs, and rapid relief of hyperglycemia toxicity can partially reduce insulin resistance and reverse beta cell function, so insulin intensive treatment can be used when newly diagnosed type 2 diabetes mellitus is accompanied by significant hyperglycemia.There are also some special circumstances that require insulin treatment: perioperative period;In case of serious acute complications or stress, temporary insulin use is required to pass the dangerous period, such as diabetic ketoacidosis, hypertonic hyperglycemia, lactic acidosis, infection, etc;Serious chronic complications, such as diabetic foot, severe diabetic nephropathy, etc;Combined with some serious diseases, such as coronary heart disease, cerebrovascular disease, blood disease, liver disease, etc;For women with gestational diabetes mellitus and diabetes mellitus complicated with pregnancy, during pregnancy, before and after delivery, and during lactation, if the blood sugar can not be controlled by diet alone to reach the required target value, insulin treatment is required, and oral hypoglycemic drugs are prohibited.Patients with secondary diabetes and specific diabetes.
2. Adverse reaction of excessive injection
If insulin is injected excessively during treatment, it will lead to hypoglycemia. When the poisoning is mild, it will mainly affect the autonomic nervous system, manifested as hunger, dizziness, paleness, weakness and sweating, and may also have tremor, precordial discomfort, facial and limb numbness and headache.When the blood sugar is further reduced, it will affect the central nervous system, and there will be voice disorder, diplopia, muscle tremor, ataxia, followed by coma and convulsions of varying degrees. This state is called insulin shock. If it is not rescued in time, it will lead to death.
Insulin injection site
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Abdomen: It is the preferred part, because the subcutaneous fat of the abdomen is thick, which can reduce the risk of injection into the muscle layer. It is the easiest to pinch the abdominal skin, and it is the fastest part to absorb insulin.It should be injected from 3 to 4 fingers on both sides of the navel. The thinner the subcutaneous layer on both sides of the body, the easier it is to penetrate the muscle layer.This site is most suitable for injection of short acting insulin or insulin mixed with medium acting insulin.
In addition, the outer side of the thigh, the outer quarter of the upper arm and the buttocks are also suitable for insulin injection.
Outer thigh: injection into the thigh can only be performed from the front or the outer side. There are many blood vessels and nerves on the inner side, so injection is not suitable.When injecting thighs, be sure to pinch the skin or use a super short (5mm) pen needle.
The outer quarter of the upper arm: this is the most unsuitable part for self injection, because the subcutaneous tissue of the upper arm is thin, which is easy to be injected into the muscle layer: when self injection occurs, the skin cannot be pinched by itself.When it is necessary to inject the upper arm, it is recommended to use a super short pen needle (5mm) or use medical staff and family members to assist in the injection.
Hips: Hips are suitable for injecting medium and long-term insulin (such as medium and long-term insulin injected before sleep), because the subcutaneous layer of the hips is thick and the absorption rate of insulin is slow, which can better control fasting blood glucose, and at the same time, there is no need to pinch the skin and no risk of intramuscular injection.
