blood glucose regulation

Question 1

what do beta cells contain for controlling insulin secretion and are they normally open or closed

Answer 1

-Ca 2+ and K+ channels
-Ca2+ channels are normally closed
-K+ channels are normally open= K+ diffuse out of cell making the inside more negative-at rest potential difference across cell membrane is -70mV

Question 2

explain how insulin secretion is controlled when blood glucose conc is high

Answer 2

1. high glucose conc outside of cell causes glucose to diffuse in by facilitated diffusion
   2.glucose is phosphorylated by glucokinase and used to produce ATP
   3.Extra ATP closes K+ channels and so K+ can no longer diffuse out
2. potential difference across membrane altered, inside of cell becomes less negative
3. change in p.d triggers opening of Ca2+ channels
4. Ca2+ enter cell and cause insulin-containing vesicles to fuse with cell membrane and release insulin by exocytosis

Question 3

why is it important to control blood glucose concentration

Answer 3

-if blood glucose becomes too high it affects the water potential of blood and can damage tissues and organs
-reduce effect of osmosis on surrounding tissue

Question 4

what might cause blood glucose levels to fall

Answer 4

-exercise
-starvation
-glycogenesis

Question 5

what is very low blood sugar and very high blood sugar called

Answer 5

-very low= hypoglycaemia
-very high= hyperglycaemia

Question 6

what might cause blood glucose levels to rise

Answer 6

-eating carbohydrates
-glycogenolysis
-gluconeogenesis

Question 7

define:
-glycogenesis
-glycogenolysis
-gluconeogenesis

Answer 7

-glycogenesis= conversion of glucose to glycogen

-glycogenolysis= conversion of glycogen to glucose

-gluconeogenesis= conversion of amino acids and glycerol to glucose

Question 8

which hormone inhibits glycogenesis

Answer 8

adrenaline

Question 9

which cells detect blood glucose rise and fall

Answer 9

rise= beta cells
fall= alpha cells

Question 10

what happens when blood glucose levels rise

Answer 10

-high blood glucose detected by beta cells
-beta cells secrete insulin
-insulin is delivered via blood to target cells in liver-hepatocytes-, muscles, other body cells and brain

Question 11

how does insulin act on target cells -hepatocytes-

Answer 11

-insulin is a small protein that is unable to pass through the phospholipid bilayer
-target cells have specific membrane bound receptors complementary to insulin
-when insulin binds to the receptor an enzyme called tyrosine kinase is activated in the cell
-activated tyrosine kinase phosphorylates inactive enzymes in the cell leading to a cascade of enzyme controlled reactions to reduce blood glucose e.g fusing of vesicles containing glucose transporter proteins with the membrane

Question 12

what are the reactions/ responses to insulin in cells to lower blood glucose conc

Answer 12

-increase in number of glucose transporter proteins on cell surface membrane
-more glucose enters cell
-glucose converted to glycogen for storage = glycogenesis
-more glucose converted to fats = lipogenesis
-more glucose used in respiration

=blood glucose conc falls

Question 13

what happens when blood glucose falls

Answer 13

-low blood glucose detected by alpha cells
-alpha cells secrete glucagon
-glucagon delivered via blood to target cells in liver
-glucagon binds specific cell membrane receptors, this stimulates a g protien which activates adenyl cyclase which converts ATP to cAMP which then activates series of enzyme controlled reactions to bring about the response of raising blood glucose

Question 14

what is the response of glucagon in cells

Answer 14

-conversion of glycogen to glucose = glycogenolysis
-more fatty acids used in respiration
-glucose produced from amino acids and fats = gluconeogenesis

Question 15

what are the major site for insulin and glucagon action

Answer 15

insulin= liver, muscle, adipose tissue

glucagon= liver