Lecture 16: Endocrine Pancreas Flashcards
What hormones does the endocrine pancreas release and from where?
Alpha Cells: Glucagon
Beta Cells: Insulin and C peptide
Delta Cells: Somatostatin
F cells: pancreatic polypeptide (satiety signal)
Endocrine cells of the pancreas are arranged in clusters called what?
Islets of Langerhans
What do delta cells look like?
Neuronal
-send dendrite like cells to beta cells
How do endocrine cells of the pancreas communicate with each other?
Gap junctions
How does blood flow in the endocrine pancreas?
Starts at the center of the islet and flows to the periphery
What type of hormone is insulin: catabolic or anabolic?
Anabolic
- promotes glucose uptake
- promotes glycogenesis, lipogenesis, and protein synthesis
What is a peptide hormone?
2 chains linked by disulfide bridges
What is the difference between preproinsulin, proinsulin, and insulin?
Preproinsulin: Signal Peptide + A and B chains + C peptide (no disulfide bonds)
Proinsulin: A and B chains + C peptide
Insulin: A and B chains
What is the significance of C peptide?
Marker of endogenous insulin secretion
-normally, secreted in equimolar quantities of insulin
Where are GLUT-2 transporters normally found?
Liver (main)
Pancreatic Beta Cells
Describe how insulin is released from beta cells?
- Glucose enters via GLUT-2
- GLU –> GLU-6-Phosphate (promotes ATP production)
- ATP closes inward-rectifying potassium channels (cell becomes more negative)
- Plasma membrane is depolarized
- Voltage gated calcium channels open
- Calcium enters cells to release insulin
Why are sulfonylurea receptors targeted for type II diabetes treatment?
Increased membrane depolarization causes increased calcium entry –> more insulin released
Describe the biphasic model of insulin release.
First phase: rapid release of insulin
Second phase: slow release of insulin
In diabetic individuals, which phase of insulin secretion does not work?
First phase
After insulin receptors are phosphorylated and complete their downstream pathways, what vesicle is translocated to the membrane?
GLUT 4
Other than insulin, activation of what can result in GLUT 4 translocation?
Activation of AMP-kinase
-muscle contractions stimulate this process
What inhibits insulin secretion?
Somatostatin
What activates glucagon secretion?
Decreased glucose levels
CCK
β-adrenergic agonists
What inhibits glucagon secretion?
Insulin (main)
Somatostatin
Fatty Acids
Ketoacids
What is the physiology behind Type I diabetes?
Destruction of β-cells
-increased blood glucose, fatty acids, and keto acids
In type I diabetes, do patients have hyperkalemia or hypokalemia?
Hyperkalemia
-insulin plays a role in Na+/K+ ATPase (not working properly)
What is the physiology behind Type II diabetes?
Insulin resistance
-exhaustion of β-cells
Describe obesity induced insulin resistance.
Decreased GLUT-4 uptake of glucose
-more insulin and glucose in blood
What are incretin hormones?
Stimulate insulin secretion to lower blood glucose levels.
- released after eating from beta cells
- intestine derived hormone (GLP-1, GIP)
