1 - insulin secretion

Question 1

normal blood glucose conc.

Answer 1

4-7mmol

Question 2

what secretes insulin

Answer 2

pancreas

Question 3

role of alpha cells

Answer 3

glucagon production

Question 4

role of beta cells

Answer 4

insulin production

Question 5

effect of eating on insulin levels

Answer 5

increase insulin conc. to keep blood glucose conc. within tight range

Question 6

exocrine/endocrine parts of pancreas

Answer 6

pancreas is mainly exocrine

however islets of langerhans are endocrine

Question 7

which 3 tissues does insulin act on to lower blood glucose

Answer 7

liver
muscle
adipose

Question 8

effect of insulin on liver tissue

Answer 8

prevents glucose production

Question 9

effect of insulin on muscle tissue

Answer 9

increases glucose uptake

Question 10

effect of insulin on adipose tissue

Answer 10

prevents lipolysis

Question 11

role of GLUT4 in muscle/adipose tissue

Answer 11

translocates to plasma membrane so more glucose can enter

Question 12

what is glucagon

Answer 12

counter regulatory hormone to insulin

prevents hypoglycemia

Question 13

action of glucagon on liver

Answer 13

decreases glycogen levels –> inhibits glycolysis and glycogenesis

increases glucose levels –> stimulates glucogenesis and glycogenolysis

Question 14

3 lifestyle effects on blood sugar

Answer 14

exercise
illness
stress

Question 15

how does stress effect blood sugar

Answer 15

parasympathetic nervous system increases insulin therefore decreases blood glucose

Question 16

where is insulin stored

Answer 16

granule cells in cytoplasm of beta cells

Question 17

response of insulin to glucose

Answer 17

2 phases:

1st - immediate/rapid high peak of insulin
2nd - lower level sustained release of insulin

Question 18

glucagon receptors in liver

Answer 18

GPCR

glucagon binds and increases cAMP and PKA

Question 19

process of nutrient stimulated insulin secretion

Answer 19

increased blood glucose

detected by beta cells and taken up via up-regulated GLUT2 (facilitated diffusion down conc. gradient)

glycolysis:
glucose metabolised by glucokinase
increased ATP

ATP-sensitive K+ channels close –> membrane depolarises

voltage-gated Ca2+ channels open –> intracellular Ca2+ conc. increases

granules fuse with membrane and release insulin by exocytosis

Question 20

importance of fatty acids on nutrient stimulated insulin secretion

Answer 20

also metabolised in the krebs cycle
therefore more ATP produced
more K+channels close

Question 21

role of GPR40 receptor

Answer 21

GPCR fatty acid receptor
acts as a nutrient sensor
binds to free fatty acids
activates pathways to increase intracellular Ca2+

Question 22

which cells contain glucose instead of hexokinase IV

Answer 22

beta cells

Question 23

what is gluokinase

Answer 23

enzyme important for setting the threshold for insulin secretion in increased glucose

catalyses glucose phosphorylation

Question 24

phosphorylated glucose =

Answer 24

glucose-6-phosphate

Question 25

how is glucokinase different from hexokinase IV

Answer 25

it has low affinity for glucose therefore the glucose conc. has to be very high it is not inhibited by the substrate

Question 26

properties of beta cells

Answer 26

GLUT2 transporter (low affinity for glucose) vascularised islets for good blood supply controlled number highly specialised with unique transcription factors

Question 27

transcription factors specific to beta cells

Answer 27

PDX-1 NeuroD1 Nkx6

Question 28

GLUT2 adaptations

Answer 28

high capacity for glucose low affinity for glucose acts as a glucose "sensor"

Question 29

process of insulin uptake into cells

Answer 29

insulin binds to tyrosine kinase receptor RTK transautophosphorylates and dimerises IRS-1 signals to intracellular pathways PIP2 --> PIP3 (recruits Akt kinase) PDK-1 and PKB cause GLUT4 vesicles to move to membrane and uptake glucose

Question 30

role of IRS-1 | insulin receptor substrate

Answer 30

signalling adaptor protein signals from insulin/IGF-1 to intracellular signalling pathways such as PI3K/Erk/MAPK phosphorylation by RTK produces binding sites via SH2 domains

Question 31

process of glucagon secretion | at low glucose conc.

Answer 31

``` glucose cleaves GLUT1 transporter K+/ATP channel closes membrane depolarises voltage-gated Ca2+ channels open --> increased intracellular Ca2+ glucagon secreted from vesicles ```

Question 32

process of glucagon uptake

Answer 32

G-alpha-s --> adenyl cyclase --> cAMP --> pKA phosphorylation by glycogen phosphorylase - -> glucose-1-phosphate - -> glucose-6-phosphate glycogenolysis

Question 33

role of amino acids in insulin secretion

Answer 33

enter straight into krebs cycle for metabolism

Question 34

GLP-1

Answer 34

incretin released from gut acts on Beta cells to increase insulin secretion and decrease blood sugar 2nd messenger = cAMP

Question 35

how does parasympathetic NS effects glucose conc

Answer 35

cephalic stage of digestion stimulates insulin secretion