Mr p bio 9 homeostasis Flashcards
what does a feedback loop do?
informs the receptor of the changes to the system brought about by the effector.
what is negative feedback?
When there is a change away from the normal level/set point.
Effectors act to opposes the change to bring the level back to norm/set point.
what is positive feedback?
A change is amplified – a change causes further change – moves further away from the set point/norm.
why is positive feedback not always involved in homeostasis?
it doesn’t keep your internal environment stable within restricted limits.
why does homeostasis involve multiple negative feedback mechanisms?
for each factor being controlled.
Having more than one mechanism gives increased control over changes in your internal environment.
Having multiple negative feedback mechanisms means you can actively increase or decrease a level so it returns to normal, rather than just control the factor in one direction.
when does blood glucose level fall and rise?
Rises after eating food containing carbohydrates.
Falls after exercise, as glucose is used in respiration for the release of energy.
what hormones are used in blood glucose control?
Insulin and glucagon
where are Insulin and glucagon secreted from?
a cluster of cells in the pancreas called the islets of Langerhans.
how does insulin lower blood glucose?
- binds to receptors on membranes of muscle and liver cells
2.Increases membrane permeability to glucose so more glucose absorbed – by increasing no. of glucose carrier proteins in cell surface membrane
3.Activates enzymes in muscle and liver cells that convert glucose into glycogen which is stored in cytoplasm – glycogenesis.
4.Increases the rate of respiration of glucose in muscle cells.
how does insulin’s process decrease blood glucose?
reduce the concentration of glucose in the cell so maintains the conc. gradient, meaning more glucose diffuses into the cell by facilitated diffusion.
what is glycogenesis?
making glycogen from glucose in the liver
how does glucagon increase blood glucose?
- Binds to specific receptors on the membrane of hepatocytes and activates enzymes that hydrolyses glycogen to glucose – glycogenolysis
- Activates enzymes involved in the formation of glucose from glycerol and from amino acids – gluconeogenesis.
3.Glucagon decreases the rate of respiration of glucose in cells.
what is glycogenolysis?
Hydrolysing glycogen in the liver to glucose
what is gluconeogenesis?
making glucose from glycerol and amino acids in the liver
name 3 differenes between a hormonal response + a nervous response
1.Hormones travel in the blood to target organs = slower response than nervous one.
2.Also means response is widespread to all target organs/cells unlike localised nervous one.
3.longer response as hormones broken down slower than neurotransmitters.
when and where is adrenaline secreted?
Increased secretion from adrenal glands when blood glucose conc. is low/ stressed/ exercising.
how does adrenaline increase blood glucose?
Binds to receptors on the cell membrane of hepatocytes and increases blood glucose levels by:
1.Activating glycogenolysis.2.Inhibiting glycogenesis .
3.Activates glucagon secretion
4.Inhibits insulin secretion.
what is the second messenger model?
1.Adrenaline and glucagon bind to respective specific receptors, which activates enzyme called adenylate cyclase.
2.Activated adenylate cyclase converts ATP into a chemical called cyclic AMP (cAMP), which is a second messenger.
3.cAMP activates enzyme: protein kinase A.
4.Protein kinase A activates a cascade (chain of reactions) that hydrolyses glycogen into glucose.
what is type one diabetes?
Person does not make insulin – usually from birth
NEED MORE
what is type two diabetes?
Person makes insulin
Less receptors for Insulin (may still be some present)
