Exam 3- The Endocrine Pancreas Flashcards
what nerves innervate the pancreas?
sympathetic and parasympathetic nerves
synapse directly on pancreatic cells
what does the sympathetic nervous system stimulate in the pancreas?
glucagon release
inhibits insulin release
what are the functional units of the endocrine pancreas?
islets of langerhans
what mass of the pancreas does the endocrine pancreas make up and how much of the overall pancreatic blood flow does it receive?
2%
10%
what are the cell types in the islets of langerhans?
alpha cells
beta cells
delta cells
F cells
what do alpha cells secrete?
glucagon
what do delta cells secrete?
somatostatin
how do cells communicate in the islets of langerhans?
gap junctions
blood supply
innervation
what is unique about the blood supply of the islets of langerhans?
arteriole enters center, spreads out it network fenestrated capillaries, then converges into venules
carries insulin from beta cells to alpha and delta cells
what cells perform regulatory functions from inside the islets of langerhans?
delta cells send dendrite-like processes onto beta cells
what is the overall structure of insulin?
peptide hormone: A and B chains with connecting peptide
2 disulfide bonds between A and B chains, one more within A chain
what electrolyte is important for releasing insulin from the secretory granules?
calcium
what is released with insulin from the granules?
C-peptide in equal proportion
true/false: insulin activity is highly species specific
false
what is the first step of insulin synthesis?
translation of mRNA
what transporter is on beta cells that allows glucose into the cells?
GLUT2: facilitated diffusion
what happens to glucose inside of the pancreatic beta cell?
phosporylated to glucose-6-phosphate by glucokinase
what happens to glucose-6-phosphate inside the beta cell?
oxidized, producing ATP
why is the production of ATP important for secreting insulin?
it closes ATP-sensitive K+ channels, decreasing conductance and leading to beta cell becoming depolarized
what does depolarization of the beta cell lead to?
opening of voltage-gated Ca++ channels and increasing Ca++ concentration inside the cell
what does increased Ca++ concentration inside the beta cell lead to?
Ca++ mediated exocytosis of insulin-containing granules
is oral or intravenous glucose a stronger stimulator of insulin secretion?
oral glucose
what hormones does oral glucose stimulate?
glucose dependent insulinotropic peptide (GIP) and glucagon-like peptide 1 (GLP-1)
what is the structure of the insulin receptor?
tetramer with 2 alpha and 2 beta subunits
what is the mechanism of action of the insulin receptor?
insulin binds to alpha subunits
conformational change in beta subunits: activated tyrosine kinase activity
phosphorylates other proteins and enzymes
insulin-receptor complex internalized and degraded or recycled
does insulin bind to other places than the insulin receptor?
yes- in nucleus, golgi, and endoplasmic reticulum to influence gene transcription
how does insulin decrease blood glucose?
increases GLUT4 transporters in cell membranes
promotes formation glycogen from glucose in muscle and liver
inhibits glycogenolysis
inhibits gluconeogenesis
what does insulin do to blood fatty acid concentration?
lowers it: stimulates storage and inhibits lipolysis
how does insulin affect blood amino acid concentration?
increased amino acid and protein uptake by tissues
does insulin affect the hypothalamic satiety center?
yes- direct effect
what is glucagon’s primary target?
liver
what cells release glucagon?
alpha cells
what is the direction of blood flow in the pancreas?
center to periphery
dense network fenestrated capillaries
what percentage of the islet of langerhans do beta cells make up?
65%
what do F cells secrete in the endocrine pancreas?
pancreatic polypeptide
what nerves carry the sympathetic and parasympathetic innervation to the endocrine pancreas?
splanchnic nerves carry sympathetic (celiac ganglion)
vagus nerve carries parasympathetic
between what cells are gap junctions in the endocrine pancreas?
beta cells and beta cells
alpha cells and beta cells
what is the sequence of events for insulin synthesis?
translation of mRNA: preproinsulin
signal peptide cleaved: proinsulin
shuttled to endoplasmic reticulum
secretory granules in golgi
proteases cleave connected peptide
what does exercise do to insulin secretion?
inhibits it: stimulates alpha-1 adrenergic receptors on beta cells: prevents hypoglycemia
