CVD WK2 INSULN

What type of hormone is insulin?

Peptide hormone

How many chains does insulin have and how are they linked?

2 chains (α and β) linked by disulphide (S-S) bonds

What type of receptor does insulin act on?

Tyrosine kinase receptor

Which cells secrete insulin?

β-cells (beta cells) in the Islets of Langerhans

Where are β-cells located within the Islets of Langerhans?

In the centre of the islets

Where are α-cells located within the Islets of Langerhans?

On the periphery (outside) of the islets

Which cell type is the most abundant in the Islets of Langerhans?

β-cells (insulin-secreting cells)

Where is insulin secreted into?

The hepatic portal vein

What percentage of insulin is removed by the liver on first pass?

Approximately 60%

What is the major control factor for insulin secretion?

Blood glucose level

How does glucose enter the β-cell?

Via GLUT-2 transporters (facilitated diffusion)

What happens when glucose enters the β-cell?

Increased glucose inside the cell triggers insulin secretion

What is the overall effect of insulin on blood glucose?

DECREASES blood glucose

What is insulin synthesised as?

A pro-peptide (preproinsulin) by ribosomes on the RER

What is removed from proinsulin to form mature insulin?

C-peptide (31 amino acids)

What are the two chains of mature insulin called and how many amino acids do they have?

A-chain (21 amino acids) and B-chain (30 amino acids)

Is C-peptide secreted with insulin?

Yes, both insulin and C-peptide are secreted together

Why is C-peptide useful clinically?

Plasma C-peptide level is a measure of insulin secretion because it is not cleared rapidly from the blood

What are the three major target organs of insulin?

Liver, skeletal muscle, adipose tissue

What is the effect of insulin on glucose uptake into cells?

INCREASES glucose uptake (especially in skeletal muscle and adipose tissue)

What is the effect of insulin on glycogenesis?

INCREASES glycogenesis (glycogen synthesis)

What is the effect of insulin on glycogenolysis?

DECREASES glycogenolysis (glycogen breakdown)

What is the effect of insulin on gluconeogenesis?

DECREASES gluconeogenesis (new glucose production)

What is the effect of insulin on glycolysis?

INCREASES glycolysis (glucose breakdown for energy)

Which glucose transporter is insulin-dependent?

GLUT-4

Where is GLUT-4 found?

Abundant in skeletal muscle and adipose tissue

What happens to GLUT-4 in the presence of insulin?

GLUT-4 vesicles move from inside the cell to the cell membrane, increasing glucose uptake

What happens to GLUT-4 in the absence of insulin?

GLUT-4 is stored inside the cell in vesicles

Which glucose transporter is NOT insulin-dependent?

GLUT-2

Where is GLUT-2 found?

In the liver (and pancreatic β-cells)

What is the effect of insulin on fatty acid uptake?

INCREASES fatty acid uptake into adipose tissue

What is the effect of insulin on lipogenesis?

INCREASES lipogenesis (fat synthesis)

What is the effect of insulin on lipolysis?

DECREASES lipolysis (fat breakdown)

What is the overall effect of insulin on blood fatty acids?

DECREASES blood fatty acids

What is the effect of insulin on triglyceride synthesis?

INCREASES triglyceride synthesis (fat storage)

What is the effect of insulin on amino acid uptake?

INCREASES amino acid uptake into cells (especially skeletal muscle)

What is the effect of insulin on protein synthesis?

INCREASES protein synthesis

What is the effect of insulin on protein degradation (proteolysis)?

DECREASES protein degradation

What is the overall effect of insulin on blood amino acids?

DECREASES blood amino acids

Which amino acids stimulate insulin secretion?

Leucine and arginine

What is the effect of the parasympathetic nervous system on insulin secretion?

INCREASES insulin secretion

What is the effect of the sympathetic nervous system on insulin secretion?

DECREASES insulin secretion

Which gut hormone (incretin) increases insulin secretion?

GLP-1 (Glucagon-like Peptide-1)

What is the mechanism of glucose uptake via GLUT-4?

Insulin causes translocation of GLUT-4 vesicles to the cell membrane

What is the role of IRS (Insulin Receptor Substrate)?

IRS proteins are phosphorylated by the insulin receptor and trigger downstream signalling cascades

What is the difference between GLUT-2 and GLUT-4?

GLUT-2 is not insulin-dependent (liver, β-cells). GLUT-4 is insulin-dependent (muscle, adipose tissue)

What is the effect of insulin on the liver?

Stimulates glycogenesis, inhibits glycogenolysis and gluconeogenesis

What is the effect of insulin on skeletal muscle?

Increases glucose uptake, glycogenesis, and protein synthesis

What is the effect of insulin on adipose tissue?

Increases glucose and fatty acid uptake, stimulates lipogenesis, inhibits lipolysis

What is the overall metabolic state promoted by insulin?

STORAGE (fed state) - stores glucose as glycogen, fats as triglycerides, and amino acids as protein