Exam #4: Endocrine Physiology Flashcards
What are the cell types found in the pancreatic islets?
Alpha Beta Delta Epsilon PP of F
What hormones are secreted by the alpha cells of the pancreatic islets?
glucagon
proglucagon
What hormones are secreted by the beta cells of the pancreatic islets?
Insulin Proinsulin C-peptide IAPP GABA
What hormones are secreted by the delta cells of the pancreatic islets?
Somatostatin, negative regulator of insulin secretion
What hormones are secreted by the epsilon cells of the pancreatic islets?
Ghrelin
What hormones are secreted by the F cells of the pancreatic islets?
Pancreatic polypeptide
What are the biosythetic steps of insulin?
1) Insulin gene translated to preproinsulin in ER
2) Preproinsulin is cleaved immediately
3) Proinsulin is packaged into secretory vesicles
4) Conversion of proinsulin to insulin and C-peptide in the secretory vesicles
*Thus, C-peptide and insulin are secreted together. C-peptide is an emerging area of research & a marker of insulin secretion.
What is the half-life of insulin?
3-5 min because it circulates in a unbound form, which gives it a short half-life
What are the stimulators of insulin? Outline the mechanisms of insulin secretion by these stimulators.
Glucose= most potent stimulator of insulin release
- Glucose moves down its concentration gradient into the pancreatic beta cell; this increase in intracellular glucose leads to an increase in ATP/ ADP ratio
- Increased ATP/ADP ratio leads to closing of a K+ channel
- Beta cell membrane leads to DEPOLARIZATION b/c of the accumulation of K+ (positive charge) on the inside of the cell
- Sensed by a voltage-gated Ca++ channel
- Ca++ rushes in
- Insulin vesicles are exocytosed
Vagal stimulation
- ACh activates muscarininc 3 receptors
- Gq
- PLC
- Intracellular Ca++ increase leads to vesicular docking and insulin release
What are the amplifiers of insulin?
Hormones
- Glucagon like peptide (GLP1)*****
- Gastric inhibitory peptide (GIP)
- Cholecystokinin (CKK)
- Gastrin
- Secretin
Catecholamines
- B-adrenergic stimulation i.e. an epinephrine surge
What are the inhibitors of insulin?
Hormones
- Somatostatin
Catecholamines
- alpha-adrenergic stimulation
- SNS
What are the cellular events that occur following activation of the insulin receptor?
1) Insulin binds to the insulin receptor
2) Activation of large number of intracellular molecules
3) Promotion of GLUT4 transporters insertion into the membrane so glucose can flow down its concentration gradient into the cell
Insulin receptors regulate mitogenic and metabolic processes
What tissues utilize glucose transporters for the cellular uptake of glucose?
GLUT4 is the glucose transporter that is regulated by insulin, the other transporters ARE NOT
- Skeletal muscle
- Adipose tissue
What are the metabolic consequences of insulin in the liver?
1) Promotion of anabolism
- Glycogen synthesis & storage
- Inhibition of glycogen breakdown
- Increased protein synthesis
- Increased triglyceride synthesis
2) Inhibition of catabolism
- Inhibit glyocogenolysis
- Inhibit ketogenesis (fat to FFA)
- Inhibit gluconeogenesis
*Generally, you’re promoting the formation of bigger molecules and the breakdown of bigger molecules into smaller ones
What are the metabolic consequences of insulin in the adipose tissue?
Increased triglyceride storage by:
- Promoting FFA uptake
- Promoting esterification of FFA
- Inhibition of lipolysis
