Glucose Homeostasis

Question 1

What classes as hypoglycaemia?

Answer 1

when blood glucose falls below normal levels of 4-5mmol/L

Question 2

What happens to cerebral function during hypoglycaemia?

Answer 2

it is increasingly impaired

Question 3

what happens if blood glucose concentration falls below 2mmol/L?

Answer 3

unconsciousness, coma and death

Question 4

what blood glucose concentration range is classed as normoglycaemic?

Answer 4

4-7mmol/L

Question 5

Which 4 hormones are involved in increasing our blood glucose from a low level?

Answer 5

glucagon - pancreas
cortisol
GH - growth hormone
catecholamines

Question 6

which cells in the pancreas are involved in exocrine secretions? What are exocrine secretions? What percentage of the pancreas does this?

Answer 6

exocrine acinar cells
enzymes that help with digestion
98%

Question 7

How are exocrine secretions secreted?

Answer 7

via duct to small intestine

Question 8

what percentage of the pancreas is made up of islets of langerhans?

Answer 8

2%

Question 9

what do alpha cells secrete?

Answer 9

glucagon

Question 10

what do beta cells secrete?

Answer 10

insulin

Question 11

what do delta cells secrete?

Answer 11

somatostatin

Question 12

what is a gap junction?

Answer 12

allows small molecules to pass directly between cells

Question 13

what is a tight junction?

Answer 13

small intercellular spaces

Question 14

what is the function of insulin?

Answer 14

reduce blood glucose, stimulate growth and development

Question 15

what is the function of glucagon?

Answer 15

increases blood glucose

Question 16

what is the function of somatostatin?

Answer 16

inhibits both insulin and glucagon

Question 17

which factors other than blood glucose stimulate the beta cells to secrete insulin?

Answer 17

some amino acids
some GI hormones
parasympathetic nervous system activity (digestion)

Question 18

what effect does the sympathetic nervous system have on beta cells?

Answer 18

decreases insulin secretion via alpha cells by switching off their receptors
some minor stimulation by beta adrenergic receptors

Question 19

What does insulin cause?

Answer 19

build up of glycogen stores
breakdown of glucose
uptake of glucose
increases amino acid transport
increases protein synthesis
reduces breakdown of fat and increases storage of fat

Question 20

which factors increase glucagon?

Answer 20

decrease in blood glucose
some amino acids
some Gi hormones
SNS activity via alpha cells
PNS activity

Question 21

what does glucagon do?

Answer 21

Increase breakdown of fats to form more glucose
Increase amino acid transport into the liver to form more glucose (gluconeogenesis)
helps break down glycogen stores in the liver (hepatic glycogenolysis)

Question 22

Is GLUT-2 transporter insulin sensitive?

Answer 22

no

Question 23

how is glucose first metabolised once it enters the cell?

What is it eventually converted into?

Answer 23

converted to glucose-6-phosphate by hexokinase IV (glucokinase) - this is the rate limiting step as it depends on how much glucose is in the blood
ATP

Question 24

What does ATP do to ATP sensitive K+ channels during glucose uptake into beta cells and what affect does this have on the cell?

Answer 24

blocks them
which leads to increase in intracellular K+ levels, causing depolarisation
which stimulates Calcium voltage gated channels which causes influx of calcium ions

Question 25

how does influx of calcium affect the beta cell?

Answer 25

causes release of insulin and synthesis of insulin

Question 26

what do we usually measure when we want to test someone’s ability to produce their own insulin and why/

Answer 26

c-peptide
insulin assays aren’t as stable and more difficult to measure, c-peptide is easier to determine
c-peptide is the by-product produced during proteolytic cleavage of proinsulin

Question 27

what is the ‘incretin’ effect?

Answer 27

more insulin is released when glucose is given orally than when glucose is given intravenously due to the increased release of gut hormones that stimulate insulin release

Question 28

which is the key hormone involved in the incretin effect?

Answer 28

glucagon like peptide-1 (GLP-1)

Question 29

when is GLP-1 secreted and how is it produced?

Answer 29

in response to nutrients in the gut

transcription product of pro-glucagon gene, mostly from L-cell within stomach

Question 30

How does GLP-1 work?

Answer 30

stimulates insulin, suppresses glucagon

increases satiety

Question 31

why does GLP-1 have a short half life?

Answer 31

due to rapid degradation from enzyme dipeptidyl peptidase-4 (DPPG-4)

Question 32

what are GLP-1 levels like in people with diabetes mellitus?

Answer 32

low

Question 33

how can we utilise GLP-1?

Answer 33

administer injections to individuals with diabetes to promote satiety and increase insulin secretion

Question 34

what is first phase insulin release and how does it differ in those with diabetes?

Answer 34

release of stored insulin
people with type 2 diabetes have less stored insulin and have to synthesise new insulin which they cannot secrete fast enough to make a surge

Question 35

which part of the insulin receptor does insulin bind to?

what happens?

Answer 35

extracellular domain (because it is a very large peptide) of alpha subunit
causes a conformational change in the tyrosine kinase domains of the beta subunits