HUBS 191 Lecture 29 Flashcards
(45 cards)
why are brain cells so dependent on glucose
because unlike other cells they aren’t able to use alternative substrates to produce ATP
what can prolonged high BGLs cause
blood vessel and nerve damage
where is the pancreas located and what does it consist of
it is located in the curve of the duodenum (the first part of the small intestine) and it consists of a head, tail and body
99% of pancreatic cells are clustered into ___ that secrete _______ into ducts which empty into the duodenum
acini - digestive enzymes
what are the clusters of endocrine cells in the pancreas called and how many are typically in the human pancreas
islets of langerhans or pancreatic islets - there are normally 1-2 million islets in the pancreas
what are the two types of pancreatic endocrine cells that you need to know for HUBS 191
alpha and beta cells
what do alpha cells secrete and what do they secrete it in response to
they secrete glucagon in response to low blood glucose which increase BGL back to normal
what do beta cells secrete and what do they secrete it in response to
they secrete insulin in response to high blood glucose which reduces BGL back to normal
how is insulin synthesised
insulin is a protein hormone that is initially synthesised on the rough ER of beta cells as preprohormone with A, B and C chains. the C chain is removed in the Golgi and packaged into secretory vesicles to be exocytosed into the blood
is insulin bound in circulation and how long does it remain in circulation for
insulin circulates unbound in plasma and is mostly cleared from circulation within 10-15 minutes
how can the C chain of insulin be useful
if someone is administering their own insulin we can look for the C chain to see if they are producing any of their own insulin because artificial insulin doesn’t contain any of the C peptide chain
does insulin correct hypo or hyperglycaemia
hyperglycaemia - increased BGL
how does insulin correct hyperglycaemia
by facilitating glucose uptake into cells of most body tissues. without insulin glucose can’t be utilised by most cells for energy and blood glucose level will be too high
what happens when BGLs go up
released insulin binds to insulin receptors which triggers a cascade of reactions that results in transporters that are stored inside cells like muscle and fat cells being incorporated into the plasma membrane
what tissues have different glucose transporters and therefore don’t rely as heavily on insulin
the liver and brain
what are insulin receptors made up of
alpha and beta subunits
how do insulin receptors function
insulin binds to the alpha subunit which causes beta subunits to then get the phosphate groups from ATP for themselves. beta subunits are then able to phosphorylate proteins inside the cell that mediate insulins effects (insulin response substrates) - this leads to the insertion of GLUT4 transporters into the cell membrane of muscle and fat cells
what are the effect of insulin on skeletal muscle
increased glucose energy into muscle cells via GLUT4
increased glycogen synthesis (glycogenesis)
increased transport of amino acids into the muscle and other cells
increased protein synthesis
inhibition of protein breakdown
why do muscle store glucose in the form of glycogen
glycogen doesn’t exert an osmotic effect unlike glucose which would cause water to be drawn into the cell
what are the effects of insulin in adipose tissue
increased glucose transport via GLUT4
increased synthesis and storage of triacylglycerides
insulin inhibits lipolysis - stops the breakdown of fatty acids and triglycerides
what are the effects of insulin on the liver
uptake of glucose and conversion to glycogen
fatty acid synthesis
inhibits glyconeogenesis
suppresses the formation of ketone bodies
what is the entry of glucose into hepatocytes (liver cells) dependent on
GLUT2 which is insulin independent
why does insulin increase fatty acid synthesis in the liver
when the quantity of glucose entering the liver cells is more than can be stored as glycogen (or used for hepatocyte metabolism) then insulin promotes the conversion of excess glucose into fatty acids
can fatty acids in the liver be used by other parts of the body
yes - fatty acids are packaged into VLDL as a triglyceride. VLDL enters the bloodstream and transports triglycerides to other tissues
