Control of blood glucose concentration Flashcards
how is blood glucose concentration controlled?
regulated by negative feedback
Blood glucose concentrations vary depending on food intake and energy requirements, however the concentration needs to be homeostatically controlled. It fluctuates within the normal range of 90mg in every 100cm cubed of blood
what is hyperglycaemia?
when blood glucose concentration rises too high
eg after a carbohydrate meal
describe what happens when blood glucose is too high?
- rise in blood glucose concentrations vary is detected by beta cells in the islets of langerhans within the pancreas
- beta cells secrete insulin into the blood
- alpha cells stop producing glucagon
- insulin lowers blood glucose concentrations vary depending by binding to receptor proteins found on the plasma membrane of liver, fat and muscle cells
- more glucose transport proteins are placed on the cell surface membrane (GLUT4 proteins)
- more glucose can therefore enter cell
- more glucose in the cell is converted to glycogen in glycogenesis
- more glucose used in respiration
what is Hypoglycaemia?
when blood glucose concentrations fall too low
describe what happens after blood glucose concnetrations fall to low
- alpha cells within the islets of langerhans in the pancreas detect this and release the hormone glucagon
- beta cells of the pancreas stop releasing insulin
- glucagon raises blood glucose concentraion by binding to receptors of the plasma membrane of the liver cells to convert the stored glycogen into glucose in glycogenolysis
- the glucose diffuses out of the liver cells into the blood
- target cells take up less glucose and the rate of respiration of glucose decreases
- glucagon also activates enzymes that are involved in the formation of glucose from non-carbohydrates (eg glycerol and amino acids)
- this is called gluconeogenesis
what are GLUT4 proteins?
- channel proteins which allow glucose to be transported across a plasma membrane
- found in skeletal and cardiac muscle cells
when insulin levels are low, GLUT4 is stored in vesicles in the cell cytoplasm. When insulin binds to receptors on the plasma membrane however, it causes themovement of GLUT4 to the membrane. Glucose can then be trasnported into the cell through the GLUT4 protein by facilitated diffusion
what is adrenaline?
a hormone secreted from the adrenal glands
when is adrenaline secreted?
when:
- theres a low concentration of glucose in your blood
- you are stressed
- you are exercising
what does adrenaline do?
binds to receptors in the plasma membrane of liver cells and does these things to increase blood glucose concentration
- activates glycogenolysis
- inhibits glycogenesis
it also activates glucagon secretion and inhibits insulin secretion. Adrenaline gets the body ready for action by making more glucose available for muscles to respire
what are first and second messengers?
- adrenaline and glucagon are first messengers, they activate glycogenolysis inside a cell, even though they bind to receptors on the outside
- they bind to hormone receptors, this activates an enzyme on the inside of the plasma membrane, which then causes a chemical to be produced
- this chemical is known as a second messenger
what is the second messenger that is activated by adrenaline and glucagon called?
cyclin AMP (cAMP)
what is the mode of action of adrenaline and glucagon?
- adrenaline or glucagon is the first messengers
- they are unable to enter the target cells
- adrenaline or glucagon binds to their complememtray shaped receptor proteins in their plasma membrane of target cells
- binding activates the enzyme adenylate cyclase which converts ATP to cAMP - the second messenger inside the cell
- cAMP activated a protein callef protein kinase A
- this starts a cascade of enzyme actions within the cell that causes glycogen to be broken down into glucose (glycogenolysis)
fill in the summary table
