Insulin and Glucagon PDF

Endocrine Part of Pancreas ( Islets Of Langerhans) Dr. Sherif Diaaeldin QUIZ next week (10 marks)  Endocrine Part of Pancreas ( Islets Of Langerhans) Endocrine part of pancreas constitute 1- 2% of pancreatic tissue. Hormones secreted by the pancreas are:- Insulin: Secreted...

Endocrine Part of Pancreas ( Islets Of Langerhans) Dr. Sherif Diaaeldin QUIZ next week (10 marks)  Endocrine Part of Pancreas ( Islets Of Langerhans) Endocrine part of pancreas constitute 1- 2% of pancreatic tissue. Hormones secreted by the pancreas are:- Insulin: Secreted from β cells. Glucagon: secreted from α cells. Somatostatin: Secreted from D cells of the pancreas and has inhibitory effect on insulin and glucagon secretion Pancreatic polypeptide: secreted from F cells. Pancreatic hormones are not under control of pituitary gland.  Insulin The glucose transporters Glucose enter the cells by facilitated diffusion i.e., a carrier protein called glucose transporter, or GLUT moves glucose down its concentration gradient from ECF into the cell without need to energy.  MECHANISM OF INSULIN SECRETION The beta cells have a large number of glucose transporters that permit glucose influx. Once inside the cells, glucose is oxidized to form adenosine triphosphate (ATP), which inhibits the ATP-sensitive potassium channels of the cell. Closure of the potassium channels depolarizes the cell membrane, thereby opening voltage-gated calcium channels this effect produces an influx of calcium that stimulates fusion of the insulin-containing vesicles with the cell membrane and secretion of insulin into the extracellular fluid by exocytosis. 7 types of GLUTs were discovered. The GLUT4 is the only one that is stimulated by insulin and is kept in vesicles in the cytoplasm of insulin sensitive cells.  Insulin is secreted from b –cells of the pancreas upon stimulation by the following factors: 1. Increased blood glucose level: It is the major stimulus of insulin release. It increase both release of preformed hormone as well as synthesis of new hormone. 2. Increased amino acid level in the blood: Some amino acids like arginine are potent stimulants for insulin release 3. Gut hormones: Gastric inhibiting peptide (GIP), Gastrin, and cholycystokinin increase insulin release. This explains why oral glucose stimulates insulin release more than I.V glucose 4. Parasympathetic stimulation Insulin exert the following effects: (A) Carbohydrate metabolism ‫هرمون التخزين والبناء‬ Increasing glucose utilization by the cells, thus blood glucose level is decreased. ❖ Increased glucose uptake by insulin sensitive tissue which are rich in GLUT4 e.g., all types of muscle, bone, skin, and adipose tissue. ❖ Increased glucose oxidation by body cells ❖ In the liver, insulin hormone causes an increase in glycogen synthesis, decrease glucogenolysis and gluconeogenesis. ❖ In the skeletal muscle, insulin hormone increase glycogenesis. (B) Lipid metabolism Increase storage as fat by adipose tissue cells and liver. Inhibits lipolysis. Inhibits ketogenesis. (C) Protein metabolism ‫يساعد على النمو‬ Increase uptake of amino acids into the cells and increase protein synthesis in the muscle and liver. Decrease protein catabolism. Treated  Glucagon Glucagon is secreted from a- cells of the pancreas in response to: 1. Decreased blood glucose level. e.g., during fasting. 2. Some amino acids ( alanine). 3. Gut hormones ( CCK, gastrin & GIP ). Functions of glucagon is to increase blood glucose level. This occurs by: 1. Breakdown of glycogen stores in the liver to glucose. 2. Synthesis of new glucose from gluconeogenic amino acids or glycerol (.i.e. gluconeogenesis) 3. Inhibition of glucose utilization by fat cells & skeletal muscle. 4. Lipolysis  After meals During fasting Glucagon Insulin Decreaase blood sugar Glucose Glucose Glucose Glucose Glucose Glycogen Glucagon release Glucose from the Cardiac pancreas muscle Liver Fat Skeletal cell muscle Decreaase blood sugar Increased blood Glucose sugar Glucose  Diabetes Mellitus It is the commonest endocrine disorder in the population. It is characterized by decreased body ability to metabolize glucose. It has the following symptoms & signs:- 1. Hyperglycemia. 2. Poluria. 3. Polydypsia. 4. Weight loss. It is caused by:- 1. Decreased insulin secretion by pancreas (Type I diabetes). 2. Insulin resistance ( Type II diabetes).  Type I & type II diabetes Type I Type II Onset Young age Middle age Incidence Less common More common 20% 80% Insulin level Low Normal, but tissue sensitivity is decreased Severity Severe Moderate hyperglycemia hyperglycemia Diabetic frequent Less common coma Management Insulin injection Diet control weight control