Glucose Homeostasis: Insulin Flashcards
What is the main hormone involved in glucose metabolism?
Insulin
Insulin is important in control of which two supply storages?
Fats and Proteins
Insulin is a peptide hormone. True or False
True
Insulin consists of 2 chains - alpha and beta. What bond is the chains linked by?
S-S bonds
Insulin acts as what kind of receptors?
Tyrosine kinase receptors
Where is Insulin secreted from?
Secreted from beta-cells in the Islets of Langerhans in the endocrine pancreas into the hepatic portal vein.
Insulin is synthesised as a pro-peptide by ribosomes located on the _________ ___________ ____________.
Rough endoplasmic reticulum
What does the processing of Insulin Synthesis involve?
- Folding and formation of disulphide bonds
- Removal of the C peptide (31aa) to give 2 chains (A-21aa and B30aa) linked by disulphide bonds.
Plasma C peptide level is a measure of what?
Is a measure of insulin secretion as, unlike insulin, it is not cleared rapidly from the blood.
Insulin is not stored until secretion is stimulated. True or False
False - It is stored
The major control factor for insulin secretion is level of blood glucose by which pathway?
Negative feedback pathway
How is Insulin secretion controlled after a meal?
- After a meal glucose concentration increases
- Glucose diffuses into the pancreatic beta-cell (via GLUT-2)
- Increased glucose concentration in the cell causes secretion of insulin
- Insulin causes a decrease in blood glucose
- Decreased glucose in the beta-cell decreases insulin secretion
What 3 factors can influence insulin secretion?
- 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
Why is insulin secreted after a meal?
Due to an increase in blood glucose.
Insulin acts to decrease blood glucose and what else?
Fatty acids and amino acids
How does insulin decrease blood glucose?
It decreases blood glucose by increasing the uptake into cells and utilisation of glucose
Which organs does insulin target?
- The liver
- Skeletal muscles
- Adipose tissue
How does insulin work in the liver?
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.
What are the simple steps in Glucose Homeostasis?
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
Increased uptake of glucose is mediated a insulin-dependant facilitated glucose transporter called _________.
GLUT-4
Does glucose require a transporter to move through the plasma membrane?
Yes - GLUT transporters
What does GLUT transporters allow glucose to do?
GLUT transporters allow facilitated diffusion of glucose down its concentration gradient.
In the presence of insulin, what happens to GLUT-4?
GLUT-4 moves from inside the cell to the cell membrane and therefore increases the uptake of glucose.
Where is GLUT-4 abundant?
Skeletal muscle and adipose tissue
In the liver, glucose uptake is via which transporter?
GLUT-2
GLUT-2 is insulin dependant. True or False
False
When insulin lowers blood fatty acids, it increases the synthesis of ______________.
Triglycerides
What is the process of triglyceride synthesis?
- Increase of fatty acid uptake into adipose tissue
- Increase uptake of glucose into adipose cells where it is used for de novo synthesis of fatty acids and glycerol (–> triglycerides)
- Decreases lipolysis
