Insulin Mechanism of Action

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Questions and Answers

What is the mechanism by which incretins increase insulin secretion?

Via the activation of G-protein-coupled receptors (correct)

Through the activation of calcium-induced endocytosis

By reducing the levels of cAMP

Through the inhibition of glucagon secretion

What is the role of the arcuate nucleus of the hypothalamus in regulating glucose metabolism?

To increase glucagon secretion

To regulate islet hormone secretion

To sense nutrient availability and relay neural signals to the liver (correct)

To decrease insulin secretion

How does a lack of insulin affect glucose levels in the blood?

Glucose is circulated in the blood, and excess glucose is secreted by the kidneys (correct)

Glucose is used for lipid metabolism

Glucose levels decrease in the blood

Glucose is taken up into cells more efficiently

What is the primary mechanism by which insulin regulates glucose metabolism?

By promoting glucose uptake into cells Signup and view all the answers

What is the primary mechanism by which incretins regulate islet hormone secretion?

By stimulating insulin secretion Signup and view all the answers

What is the result of insulin binding to specific membrane receptors on target cells?

Initiation of cascades of phosphorylation reactions Signup and view all the answers

What is the fate of glucose in the cell after insulin-mediated glucose uptake?

It is trapped as glucose-6-phosphate Signup and view all the answers

What is the effect of insulin on glycogenolysis, lipolysis, and proteolysis?

It inhibits all three processes Signup and view all the answers

What is the response to insulin binding to specific membrane receptors on target cells in terms of glucose transporters?

Intracellular vesicles containing a glucose transporter (GLUT-4) fuse with the plasma membrane Signup and view all the answers

What is the result of insulin-mediated inhibition of glycogenolysis, lipolysis, and proteolysis?

Decreased glucose release from stored glycogen Signup and view all the answers

What is the primary mechanism of insulin release in response to a meal?

Increased parasympathetic activity stimulating the release of stored insulin Signup and view all the answers

Which of the following would NOT inhibit insulin release?

Glucagon-like peptides Signup and view all the answers

What is the primary function of somatostatin in relation to insulin release?

Inhibiting insulin release and promoting glucagon release Signup and view all the answers

What is the reason why insulin must be administered parenterally to treat diabetes?

Insulin is rapidly digested in the gut with a half-life of only a few minutes Signup and view all the answers

What is the primary stimulus for the release of glucagon-like peptides from the digest tract?

Presence of food in the gut Signup and view all the answers

Study Notes

Insulin

Biological duration of action: 2-4 hours
Facilitates removal of glucose from blood into muscle and fat cells
Binds to specific membrane receptors on target cells and activates tyrosine kinase enzyme
Initiates cascades of phosphorylation reactions leading to many kinase and phosphatase activities, as well as DNA transcription and cell replication
Increases glucose uptake into cells, 'trapping' it as glucose-6-phosphate
Inhibits glycogenolysis, lipolysis, and proteolysis

Glucagon

Hormone secreted by alpha cells in the pancreas in response to hypoglycaemia and high-protein meals
Stimulates hepatic glycogenolysis and gluconeogenesis, lipolysis, and ketogenesis
Inhibits glycogen synthesis
Stimulates release of catecholamines, inhibiting tone and motility in GIT smooth muscle
Increases release of GH, ACTH, and insulin
Secretion is inhibited by insulin, hyperglycaemia, and incretins

Incretins

Peptide hormones secreted from the intestinal mucosa into the circulation in the presence of food
Increase insulin secretion via G-protein-coupled receptor activation, raised cAMP levels, and calcium-induced exocytosis
Regulate islet hormone secretion, glucose concentrations, lipid metabolism, gut motility, appetite, and body weight

Central Nervous System

Nutrient availability sensed in the arcuate nucleus of the hypothalamus
Neural signals relayed via efferent vagal fibres to the liver, inhibiting glucose production
In T2DM and obesity, the brain incorrectly perceives and responds to peripheral signals of low nutrient availability

Diabetes Mellitus

Characterized by polyuria associated with a chronic disorder of carbohydrate and lipid metabolism
Inappropriate rise in glucose level in the blood due to a relative or absolute lack of insulin
Type 1: complete lack of insulin, believed to be an autoimmune disease
Type 2: relative lack of insulin or defects of the insulin receptors due to poor diet/lifestyle, obesity, and other factors

Hyperglycaemia

Lack of insulin means glucose cannot be taken up into cells
Excess glucose circulated in blood, and excess glucose secreted by the kidneys (glycosuria)

Pancreas

Exocrine function: contains digestive enzymes, enzyme precursors, and electrolytes, discharged into the gastrointestinal tract
Endocrine function: produces hormones controlling blood glucose levels and some gastrointestinal functions
Insulin produced by beta cells, glucagon produced by alpha cells, and somatostatin produced by delta cells

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Description

This quiz covers the biological duration of action and mechanism of insulin, including its role in glucose removal and biochemical reactions in various cells.