The Endocrine Pancreas 2 (Insulin and Glucagon) Flashcards
What factors can increase insulin secretion?
Increased blood glucose concentration Presence of food within the gut Presence of certain hormones Vagal nerve activity Glucagon
What is insulin’s function?
To lower blood glucose
Where is insulin secreted from?
The pancreas
What is a Katp channel?
Specific potassium ion channel found on B-cells which is sensitive to the concentration of ATP within the cell
Through what channel does insulin enter on a B-cell?
GLUT transporter
What does an increase in glucose uptake of a B-cell cause?
Increases metabolism and thus increases the concentration of ATP via glycolysis and the critic acid cycle.
An increase in B-cell [ATP] within cells causes what?
The closure of the Katp channel
Closure of the Katp channel on B-cells leads to what?
Increase in intracellular potassium concentration leading to the depolarisation of the cell and thus voltage gated calcium channels open, triggering the release of insulin form the vesicles via exocytosis.
What second messenger does insulin then initiate on cell membranes?
Tyrosine kinase
What does insulin do to proteins?
Phosphorylates them
Where can you find GLUT-4 transporters?
In the cytoplasm of unstimulated muscle and adipose tissues
What is the function of GLUT-4 when stimulated?
Migrates to the cell membrane via exocytosis, to allow the uptake of glucose in muscle and fat cells.
Is the activation of GLUT-4 insulin dependant?
Yes, need insulin to bind to initiate the signal transduction cascade
Do most tissues require insulin to take up glucose?
No only fat and muscle, however this does make up around 60% of body weight
What is GLUT-1’s function? (and GLUT-3’s)
Required for basal glucose uptake by many cells such as brain, kidneys and RBC’s
Which transporter is required by beta-cells of the pancreas and liver to take up glucose?
GLUT-2
Are GLUT-2 transporters insulin dependant or independant? What is the consequence of this?
Insulin indépendant, therefore glucose enters down the concentration gradient
When insulin binds to its receptor on a liver cell what is the outcome of the signal cascade?
Hexokinase is activated which lowers the intracellular glucose concentration by converting it to GGP. This maintain the glucose concentration gradient
Describe the 5 anabolic or inhibiting catabolic process of of insulin
- Increases glycogen synthesis
- Increases amino acid uptake
- Increases protein synthesis
- Increases lipogenesis and inhibits lipolysis
- Inhibits the enzymes of gluconeogenesis
Give 2 non-anabolic effects of insulin
Permissive effect on growth hormone
Promotes potassium ion entry into cells by stimulating Na+/K+ ATPase
How does insulin bring about changes in cell metabolism?
Binds to receptor
Phosphorylates insulin-receptor substrates
Initiates second messier pathways, altering protein synthesis and existing proteins such as GLUT 4 to alter tenspot activity
Also up or down regulates enzymes which leads to a change in the metabolism of the cell
What is the half life of insulin?
5 minutes
Where is insulin degraded?
Liver and kidneys
What 2 enzymes are responsible for insulin degradation?
Insulin protease - breakdowns the remnants of insulin after it has been used in metabolic processes
Insulinase - breakdown free insulin in the plasma
