Endocrine Pancreas II Flashcards
What are the effects on:
Energy
Glucose
Glycogen
Fat
Protein
By Insulin and Glucagon?
How is glucose utilized during strenuous exercise?
Utilization of glucose by muscle is matched by an increase in hepatic glucose production, mediated in large part by glucagon
–> prevents hypoglycemia and provides another adjustment vital to survival in “fight or flight” situations
How is glucose utilized during serious injury or shock?
- A prompt rise in glucagon occurs together with a relatively slow insulin level, bringing about “stress hyperglycemia”
–> maximizes glucose delivery to an under-perfused brain
What types of cells are in the Islet of Langerhans? What do they secrete?
Alpha = Glucagon
Beta = Insulin
Delta = Somatostatin (SRIF)
How does somatostatin (released by delta cells) affect other cells in the islet?
SRIF coordinates the secretion of both insulin (beta cells) and glucagon (alpha cells)
- it can inhibit release of either hormone
–> ALL actions of SRIF are inhibitory
What is the process of insulin biosynthesis?
- Formation of insulin mRNA
- Ribosomal translation: synthesis into proinsulin
- Transfer of proinsulin to the golgi complex
- Packing of proinsulin to golgi complex
- Conversion of proinsuiln into insulin (posttranslational modification)
- Formation of zinc-insulin crystals
- Translocation of granules to beta cell membrane
- Fusion of granul and cell membrane
- Liberation of granule (exocytosis)
What conditions are associated with insulin resistance?
–> Decreased insulin binding occurs in:
Obesity
Mature-onset Diabetes
Growth Hormone excess
Glucocorticoid excess
Lipoatrophic diabetes
What conditions are associated with Insulin hypersensitivity?
–> Increased insulin binding occurs in:
Trained athletes
Glucocorticoid deficiency
How does insulin regulate glucose uptake by cells?
Insulin activates a series of phosphorylations and dephosphorylations that result in increased expression of GLUT 4 transporters on the surface of the cell.
- After binding, insulin and its receptor are usually internalized, constituting an “off switch” for insulin activation
- Majority of internalized hormone undergoes enzymatic degredation in the lysosomes
What are the actions of insulin on the liver?
- Stimulate glucose intake and trapping of glucose via phosphorylation by glucokinase
- Promotes storage of glucose as glycogen by activating glucogen synthase
- Reduces glucose output by inhibiting gluconeogenesis
- Reduces glucose output by inhibiting glycogenolysis through decreasing glycogen phophorylase activity
- Reduces formation of ketone bodies by decreasing beta-oxidationg of FAs
What are the actions of insulin on muscle?
- Stimulates glucose and AA uptake
- Stimulates gluocse storage as glycogen
What are the actions of insulin on adipose tissue?
- Stimulate glucose and AA uptake
- Increase the formation of alpha-glycerophosphate for FA esterification and triglyceride storage
How does insulin promote storage of FAs?
- Accelerates uptake and storage of lipid in adipocytes by stimulating lipoprotein lipase (which converts triglycerides into free fatty acids which are able to enter adipocytes)
- Facilitates glucose uptake into adipocytes (becoming a 3C backbone for TG formation
- Enhances liver FA synthesis and TG release
- Dramatically inhibits hormonally sensitive lipases in adipocytes, further reducing blood levels of free FAs
- Inhibits conversion of FA to ketoacids in hepatocytes
What stimulates insulin release?
- Glucose
- AA
- Glucagon
- Acetylcholine
- Acetylcholine
- GI hormones (i.e. Glucagon-like peptide-I)
- B2 adrenergic receptors - Epinephrine
What inhibits insulin release?
- Somatostatin
- a2 adrenergic receptor
