Pancreas Flashcards
(60 cards)
Pancreas
Islets of Langerhans cell types
All derived from pancreatic buds (embryologically)
- Alpha cells
- Beta cells
- Delta cells
Pancreatic Alpha cells
Factoids
- 20% of the islet cells
- Secret glucagon
- Located at the periphery
Pancreatic Beta cells
Factoids
- Major cell type
- Secret insulin (along with C peptide [long term marker])
- Located in the center
- Receive blood first
Pancreatic Delta cells
Factoids
- 5% of islet cells
- Secrete somatostatin
- Interspersed throughout the pancreas
Insulin
Factoids
- It is a peptide hormone
- Works through tyrosine kinase
- Anabolic
- Released along with C peptide (its long term marker)
Insulin
Effects on Glucose metabolism
- Increases glucose uptake by adipose tissue and skeletal muscles (GLUT-4)
- Increases glucose uptake by liver (by stimulating glucokinase)
- Decreases glucose breakdown
- Increases glucose storage
Insulin
Effects on Protein metabolism
- Increases amino acids uptake
- Increases protein synthesis
- Decreases protein degradation
Insulin
Effects on Fat metabolism
- Decreases hormone sensitive lipase activity
- Increases fatty acids uptake (by stimulating lipoprotein lipase)
- Increases triglycerides synthesis
- Increases acetyl CoA carboxylase enzyme activity
Insulin
Glucose storage mechanism
Through stimulating the following enzymes (by dephosphorylation):
- Glucokinase
- Glycogen synthase
- PFK-1 (via PFK-2)
- Pyruvate kinase
- Acetyl CoA carboxylase
Glucagon
Glucose release mechanism
Through stimulating the following enzymes (by phosphorylation):
- Glycogen phosphatase
- Pyruvate carboxylase
- PEPCK
- Fructose 1,6-bisphosphatase
- Glucose-6-phosphatase
Insulin
Secretion Stimuli
- Glucose
- Amino acids like arginine
- Intestinal hormones:
- GIP (gastric inhibitory peptide or glucose-dependent insulinotropic peptide)
- GLP-1 (glucagon like peptide): Exenatide is its synthetic analog
- Glucagon
- Hyperkalemia
- Dipeptidyl peptidase-IV (DPP-IV) [breaks down GLP-1] inhibitors like Sitagliptin
- Drugs that block ATP-sensitive K+ channels like sulfonylureas
Insulin
Secretion Inhibitors
- Somatostatin
- Sympathetic innervation and norepinephrine (alpha-2 receptors)
- Hypokalemia (like in hydrochlorothiazide)
Glucagon
Effects
- Glycogenolysis
- Gluconeogeneis
- Increases urea production
- Increases ketone bodies by inhibiting acetyl CoA carboxylase (though it is not the main regulator [insulin is])
- Increases lipolysis by stimulating hormone sensitive lipase
- Inotropic effect on the heart (cause it is working through Gs cAMP)
Insulin
Other Effects
- Moves K+ into cells by stimulating Na+/K+ ATPase
- Increases Na+ retention (kidneys)
- Decreases glucagon release
Glucagon
Secretion Stimuli
- Hypoglycemia
- Amino acids like arginine
Glucagon
Secretion Inhibitors
- Hyperglycemia
- Insulin
- Somatostatin
Insulin
Synthesis
- Preproinsulin synthesized in RER
- Then cleavage of presignal will produce proinsulin (insulin and C peptide) that is stored in secretory granules
Insulin
Secretion
- Increased metabolism of glucose in Beta cells will increase ATP production
- ATP will block the ATP sensitive K+ channels which results in generating an action potential (membrane depolarization)
- This depolarization will cause Ca++ entry into the cells which in turn causes cleavage of proinsulin and exocytosis of insulin and C peptide equally
Insulin-dependent glucose transports
Names and Locations
GLUT-4: in adipose tissue and striated muscles (exercise also increases their expression)
Insulin-independent glucose transports
Names and Locations
- GLUT-1: RBCs, brain, cornea and placenta (insulin does not cross the placenta)
- GLUT-2 (bidirectional): beta islet cells, liver, kidneys, and small intestine
- GLUT-3: brain and placenta
- GLUT-5 (fructose): spermatocytes and GI tract
Glucose
Hormonal Control
- When it is low, glucagon will raise it
- When it is very low, epinephrine will release glucose from liver and GH will inhibit GLUT-4 mediated uptake of glucose by the adipose tissue and skeletal muscles
- When it remains very low, cortisol will release glucose from liver and also makes amino acids from skeletal muscles available to the liver for gluconeogenesis
Diabetes Mellitus Type 1 vs. Type 2
Primary Cause, Insulin necessary for Rx, Age, Association with obesity
- 1: autoimmune destruction of Beta cells (due to glutamic acid decarboxylase antibodies [type IV hypersensitivity]). 2: increase resistance to insulin (post-receptor alternation), progressive pancreatic beta-cells failure
- 1: Always. 2: Sometimes
- 1: < 30 years. 2: > 40 years
- 1: No. 2: Yes
Diabetes Mellitus Type 1 vs. Type 2
Genetic predisposition, HLA system association, Glucose intolerance, Insulin sensitivity
- 1: Relatively weak (50% concordance in identical twins), ploygenic. 2: Relatively strong (90% concordance in identical twins), ploygenic
- 1: Yes (HLA-DR3 and -DR4). 2: No
- 1: Severe. 2: Mild to moderate
- 1: High. 2: Low
Diabetes Mellitus Type 1 vs. Type 2
Ketoacidosis, Beta-cell numbers, Serum insulin level, Classic symptoms [Presentation]
- 1: Common. 2: Rare
- 1: decreased (with islet lymphocytic infiltration [insulitis] and fibrosis). 2: variable (with islet amyloid polypeptide (IAPP) deposits)
- 1: Low. 2: variable
- 1: Common. 2: sometimes