Pancreatic islets

anatomy and physiology of pancreatic islets

1. Pancreas By Y.V.Vanaja Lecturer Vijay Marie College of Nursing

2. The pancreas is both an endocrine gland and exocrine gland. A flattened organ that measures about 12.5- 15cm in length, the pancreas is located in the curve of the duodenum, and consists of Head Body Tail Roughly 99% of the exocrine cells of the pancreas are arranged in clusters called acini . The acini produce digestive enzymes, which flow into the GI tract through a network of ducts. Scattered among the exocrine acini are 1-2 million tiny clusters of endocrine tissue called pancreatic islets or islets of Langerhans. Abundant capillaries serve both the exocrine and endocrine portions of the pancreas

3. Cell Types in the pancreas; 4 types of hormone secreting cells Alpha or A cells – constitute about 17% of pancreatic islet cells and secrete glucagon. Beta or B cells – constitute about 70% of pancreatic islet cells and secrete insulin Delta or D cells – constitute about 7% of pancreatic islet cells and secrete somatostatin F cells constitute the remainder of pancreatic islet cells and secrete pancreatic polypeptide Glucagon raises blood glucose level and insulin lowers it. Somatostatin acts in a paracrine manner to inhibit both insulin and glucagon release from neighboring beta and alpha cells. It may also act as circulating hormone to slow absorption of nutrients from the GI tract It inhibits the secretion of growth hormone Pancreatic polypeptide inhibits somatostatin secretion, gallbladder contraction and secretion of digestive enzymes by the pancreas

4. Physiology of pancreatic islets

5. Regulation of Glucagon and Insulin secretion Hypoglycemia stimulates secretion of glucagon from alpha cells of the pancreatic islets. Glucagon acts on hepatocytes to accelerate the conversion of glycogen into glucose and to promote formation of glucose from lactic acid and certain amino acids Hepatocytes release glucose into the blood more rapidly , and blood glucose level rises If blood glucose continues to rise, hyperglycemia inhibits release of glucagon

6. Insulin acts on various cells in the body to accelerate facilitated diffusion of glucose into cells To speed conversion of glucose into glycogen To i ncrease uptake of aminoacids by cells and to increase protein synthesis To speed synthesis of aminoacids To slow the conversion of glycogen to glucose from lactic acid and aminoacids . Blood glucose level falls If the blood glucose level drops below normal , low blood glucose inhibits release of insulin and stimulates release of g lucagon

7. Several hormones and neurotransmitters also regulate the release of these 2 hormones Indirectly human growth hormone ( hGH ) and adrenocorticotropic hormone (ACTH) stimulate secretion of insulin because they act to elevate blood glucose. Insulin secretion is also stimulated by; acetylcholine the neurotransmitter liberated from axon terminals of parasympathetic vagus nerve fibers that innervate the pancreatic islets The amino acid arginine and leucine , which would be present in the blood at higher levels after a protein – containing meal Glucose –dependent insulinotropic peptide , - hormone released by enteroendocrine cells of the small intestine Glucagon secretion is stimulated by; Increased activity of the sympathetic division of the ANS, as occurring during exercise a rise in blood aminoacids if blood glucose level is low, which could occur after a meal that contained mainly protein

8. Diabetes Mellitus DM is a multisystem disease related to abnormal insulin production, impaired insulin utilization, or both Types of DM; Type 1 DM Type 2 DM Type 1 DM: F ormerly known as juvenile onset or insulin dependent diabetes. Type 1 diabetes occurs because the insulin-producing cells of the pancreas (beta cells) are damaged. In type 1 diabetes, the pancreas makes little or no insulin, so sugar cannot get into the body's cells for use as energy. People with type 1 diabetes must use insulin injections to control their blood glucose. Type 1 is the most common form of diabetes in people who are under age 30, but it can occur at any age. Ten percent of people with diabetes are diagnosed with type 1.

9. Type 2 DM; In type 2 diabetes (adult onset diabetes), the pancreas makes insulin, but it either doesn't produce enough, or the insulin does not work properly. Nine out of 10 people with diabetes have type 2. This type occurs most often in people who are over 40 years old but can occur even in childhood if there are risk factors present. Type 2 diabetes may sometimes be controlled with a combination of diet, weight management and exercise. However, treatment also may include oral glucose-lowering medications (taken by mouth) or insulin injections (shots ). Gestational Diabetes; Gestational diabetes occurs when there is a high blood glucose level during pregnancy. As pregnancy progresses, the developing baby has a greater need for glucose. Hormone changes during pregnancy also affect the action of insulin, which brings about high blood glucose levels .

10. Causes; Family history of diabetes Being overweight Physical stress (such as surgery or illness) Use of certain medications, including steroids Injury to the pancreas (such as infection, tumor , surgery or accident) Autoimmune disease High blood pressure Abnormal blood cholesterol or triglyceride levels Age (risk increases with age) Smoking History of gestational diabetes

11. Signs and Symptoms; Increased thirst Increased hunger (especially after eating) Dry mouth Frequent urination Unexplained weight loss (even though you are eating and feel hungry) Weak, tired feeling Blurred vision Numbness or tingling in the hands or feet Slow-healing sores or cuts Dry and itchy skin Frequent yeast infections or urinary tract infections