Glucose Homeostasis: Insulin

Question 1

What is the main hormone involved in glucose metabolism?

Answer 1

Insulin

Question 2

Insulin is important in control of which two supply storages?

Answer 2

Fats and Proteins

Question 3

Insulin is a peptide hormone. True or False

Answer 3

True

Question 4

Insulin consists of 2 chains - alpha and beta. What bond is the chains linked by?

Answer 4

S-S bonds

Question 5

Insulin acts as what kind of receptors?

Answer 5

Tyrosine kinase receptors

Question 6

Where is Insulin secreted from?

Answer 6

Secreted from beta-cells in the Islets of Langerhans in the endocrine pancreas into the hepatic portal vein.

Question 7

Insulin is synthesised as a pro-peptide by ribosomes located on the _________ ___________ ____________.

Answer 7

Rough endoplasmic reticulum

Question 8

What does the processing of Insulin Synthesis involve?

Answer 8

• Folding and formation of disulphide bonds
• Removal of the C peptide (31aa) to give 2 chains (A-21aa and B30aa) linked by disulphide bonds.

Question 9

Plasma C peptide level is a measure of what?

Answer 9

Is a measure of insulin secretion as, unlike insulin, it is not cleared rapidly from the blood.

Question 10

Insulin is not stored until secretion is stimulated. True or False

Answer 10

False - It is stored

Question 11

The major control factor for insulin secretion is level of blood glucose by which pathway?

Answer 11

Negative feedback pathway

Question 12

How is Insulin secretion controlled after a meal?

Answer 12

1. After a meal glucose concentration increases
2. Glucose diffuses into the pancreatic beta-cell (via GLUT-2)
3. Increased glucose concentration in the cell causes secretion of insulin
4. Insulin causes a decrease in blood glucose
5. Decreased glucose in the beta-cell decreases insulin secretion

Question 13

What 3 factors can influence insulin secretion?

Answer 13

• Some amino acids (leucine, arginine)
• Autonomic nervous system (parasympathetic increases; sympathetic decreases)
• Some gut hormones (incretins) - secreted in the GI tract in response to food e.g. GLP1

Question 14

Why is insulin secreted after a meal?

Answer 14

Due to an increase in blood glucose.

Question 15

Insulin acts to decrease blood glucose and what else?

Answer 15

Fatty acids and amino acids

Question 16

How does insulin decrease blood glucose?

Answer 16

It decreases blood glucose by increasing the uptake into cells and utilisation of glucose

Question 17

Which organs does insulin target?

Answer 17

• The liver
• Skeletal muscles
• Adipose tissue

Question 18

How does insulin work in the liver?

Answer 18

Insulin is secreted into the hepatic portal vein, transporting it directly to the liver. The liver removes 60% of the insulin before it enter the systemic circulation.

Question 19

What are the simple steps in Glucose Homeostasis?

Answer 19

Insulin lowers blood glucose by:
- Glucose uptake into cells increases (skeletal muscle and adipose tissue)
- Glycogenesis in the liver and skeletal muscle increases
- Glycogenolysis decreases
- Gluconeogenesis decreases
- Glycolysis increases

Question 20

Increased uptake of glucose is mediated a insulin-dependant facilitated glucose transporter called _________.

Answer 20

GLUT-4

Question 21

Does glucose require a transporter to move through the plasma membrane?

Answer 21

Yes - GLUT transporters

Question 22

What does GLUT transporters allow glucose to do?

Answer 22

GLUT transporters allow facilitated diffusion of glucose down its concentration gradient.

Question 23

In the presence of insulin, what happens to GLUT-4?

Answer 23

GLUT-4 moves from inside the cell to the cell membrane and therefore increases the uptake of glucose.

Question 24

Where is GLUT-4 abundant?

Answer 24

Skeletal muscle and adipose tissue

Question 25

In the liver, glucose uptake is via which transporter?

Answer 25

GLUT-2

Question 26

GLUT-2 is insulin dependant. True or False

Answer 26

False

Question 27

When insulin lowers blood fatty acids, it increases the synthesis of ______________.

Answer 27

Triglycerides

Question 28

What is the process of triglyceride synthesis?

Answer 28

1. Increase of fatty acid uptake into adipose tissue
2. Increase uptake of glucose into adipose cells where it is used for de novo synthesis of fatty acids and glycerol (–> triglycerides)
3. Decreases lipolysis