What triggers Insulin release? Elevated blood glucose levels stimulate pancreatic beta cells to produce and release insulin into the circulation.

Upon entering the ER, the preproinsulin signal sequence, now useless, is proteolytically removed to form proinsulin.

Is a single-chain polypeptide with three disulfide bridges. Proteolytic cleavage of Proinsulin produces a) Insulin, which consists of 51 amino acids in two chains joined by two disulfide bridges. b) The connecting peptide (C-peptide); a single polypeptide chain containing 31amino acids.

Measurement of C-peptide provides a sensitive assessment of endogenous insulin secretion and therefore ß-cell function

1) Elevated levels of both suggest an insulinoma. 2) Elevated insulin level and low C-peptide level suggest exogenous insulin administration because commercial insulin preparations do not contain C-peptide. 3) Insulin and C-peptide measurements may be relied upon to distinguish between type 1 and type 2 diabetes.

Stimulation Inhibition

-Low dietary fuels. -Counter regulatory hormones e.g. glucagon,epinephrine, growth hormone and cortisol. -They increase plasma glucose levels by stimulating the breakdown of glycogen to glucose (glycogenolysis) and the synthesis of glucose (gluconeogenesis).

-In liver and to a lesser extent in the kidney. -By insulinase. -The separated α- and β- chains are then hydrolyzed to amino acids by proteolytic enzymes.

It is a hypoglycemic hormone : 1- It decreases blood glucose level through its uptake by most cells except the brain and hepatocytes. 2- increases its oxidation (glycolysis) and glycogenesis. 3-Insulin decreases gluconeogenesis. Effects on Carbohydrate Metabolism

It is considered an anabolic hormone, stimulates protein synthesis & positive N2-balance.

1- increase in glucose transport into adipocytes and skeletal muscles ( seconds). 2- changes in P status of existing enzymes (min to hours). 3- increase in amounts of many enzymes such as Glucokinase, PFK1 and Pyruvate Kinase (hours to days)

Glucagon is a polypeptide hormone secreted by α cells of the pancreas. It is synthesized as a large precursor molecule ( preproglucagon ) that is converted to Glucagon through a series of selective proteolytic cleavages.

Is composed of 29 AAs arranged in a single polypeptide chain

1) Low blood glucose 2) AAs derived from a meal containing protein 3) Elevated levels of circulating epinephrine and norepinephrine e.g in stress, trauma or severe exercise.

By elevated blood glucose and by insulin

a-It increased blood glucose via activation of phosphorylase b-It activates the enzymes of gluconeogenesis. c-Glucagon is a potent lipolytic hormone. The FAs are oxidized by the liver and used in ketone bodies synthesis. D- uptake of amino acids by the Liver.

Q) In which one of the following tissues is glucose transport into the cell enhanced by insulin? A. Brain. B. Lens. C. Red blood cells. D. Adipose tissue. E. Liver.

Q) Which one of the following is characteristic of low insulin levels? A. Increased glycogen synthesis. B. Decreased gluconeogenesis from lactate. C. Decreased glycogenolysis. D. Increased formation of 3-hydroxybutyrate. E. Decreased action of hormone-sensitive lipase.

Q) Which one of the following statements about glucagon is correct? A. High levels of blood glucose increase the release of glucagon from the α cells of the pancreas. B. Glucagon levels decrease following ingestion of a protein-rich meal. C. Glucagon increases the intracellular levels of cAMP in liver cells, causing an increase in glycogen breakdown. D. Glucagon is the only hormone important in combating hypoglycemia. E. Glucagon depresses the formation of ketone bodies by the liver.

Thank you and good Luck Dr. Manal Louis