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Semester 4 > case 6 - glucose and insulin physiology > Flashcards

case 6 - glucose and insulin physiology Flashcards

1
Q

where is delivery of glucose critical to

A

the CNS - it cannot substitute glucose

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2
Q

what is the stored reservoir of glucose

A

glycogen

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3
Q

what is normoglycaemia

A

4-6mmol/L
8mmol/L post-prandial (2 hrs after eating)

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4
Q

what is hypoglycaemia

A

<3mmol/L

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5
Q

what is hyperglycaemia

A

> 10mmol/L

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6
Q

what decreases blood glucose

A

glucose utilisation
energy expenditure
glucose loss <0.3g/day

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7
Q

what increases blood glucose

A

food intake - 160g/day
glucose uptake
glucose production
glucose reabsorption

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8
Q

what is insulin secreted by

A

the beta cells which are situated in the islets of Langerhans in the endocrine pancreas

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9
Q

what does insulin serve to do

A

decrease blood glucose levelds

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10
Q

what is glucagon secreted by

A

the alpha cells in the islets of langerhans

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11
Q

what is glucagon secreted in response to

A

low glucose levels and increase blood glucose levels

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12
Q

what are the glucagon sensitive tissues

A

liver
fat (adipocytes)
muscle

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13
Q

what are the insulin sensitive tissues

A

liver
fat (adipocytes)
muscle

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14
Q

what happens to our glucose levels when we have fasted

A

they are often quite low

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15
Q

what does low glucose levels trigger

A

the release of glucagon from the alpha cells

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16
Q

what also happens at low glucose levels

A

beta cells are not stimulated

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17
Q

what happens once the glucagon is released

A

it will act upon the liver to stimulate endogenous glucose production from its glycogen stores

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18
Q

where does this glucose go

A

into the blood stream

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19
Q

what are glucose levels like in the fed state and what does this stimulate

A

relatively high glucose levels, this stimulates the beta cells

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20
Q

what do these beta cells do

A

they secrete insulin

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21
Q

what does this insulin do

A

turns off glucagon production

acts on muscle and fat to increase their uptake of glucose - thus lowering blood glucose levels

it also acts upon the liver to switch of endogenous glucose production

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22
Q

what else happens when we are in the fed state

A

there are endocrine cells located within the small and large intestine called enteroednocrine cells and they are stimulated to produce hormones

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23
Q

what is the main hormone they produce and wha does it do

A

they produce GLP1. it is secreted in response to glucose load. it is an incretin hormone. GLP1 receptors are on the beta cells and this stimulated insulin secretion

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24
Q

what is T1DM

A

autoimmune destruction of beta cells

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25
Q

what is T2DM

A

defects in insulin release, sensing and/or signalling

26
Q

what is common in patients with diabetes receiving insulin

A

hypoglycaemia is common and there is a huge lack of awareness of it

27
Q

what is hyperinsulinism caused by

A

congenital defects in insulin release or insulin signalling

insulinoma

pancreatic tumours can produce too much insulin too - insulinomas

28
Q

what are the main transporters in glucose homeostasis

A

passive glucose transporters - GLUTs
sodium coupled/linked transporters - SGLTs

29
Q

what are the SGLTs

A

family of insulin insensitive transporters

30
Q

what are the two important SGLTs

A

Two are important:
- SGLT1 (SLC5A1) (2 sodiums per 1 glucose molecule per transport)
- SGLT2 (SLC5A2) (uniporter)

31
Q

what transporter has the highest affinity for glucose

A

SLGT2

32
Q

can SGLT inhibitors be used to treat diabetes

A

are approved for mono- and combination therapy of T2DM

33
Q

what mutations cause glucose-galactose malabsorption

A

SLC5A1

34
Q

what mutations cause familial glucosuria

A

SLC5A2

35
Q

what passive transporters have major functional roles

A

GLUT1, GLUT2, GLUT4

36
Q

which of these are insulin insensitive

A

GLUT1 and GLUT2 are insulin insensitive ; critical to glucose absorption and glucose signalling

37
Q

what are some features of GLUT4

A

it is insulin sensitive
found in adipose tissues, striated muscle and heart

38
Q

what are the Km values of the GLUTs

A

GLUT 4 and GLUT1 have similar Km for glucose (approx 5mM), lower than GLUT2 (17mM)

39
Q

how many transporters are in the GLUT family

A

13

40
Q

what do the GLUTs do

A

not only take glucose into the cell but also out of it aswell

41
Q

how does SGLT1 take glucose into the cell

A

takes glucose into the cells across the membrane by using 2 sodium ions

42
Q

how does glucose leave the enterocyte

A

via the passive transporters GLUT2

43
Q

what happens next to the glucose

A

it goes into the blood stream and goes into erythrocytes using the GLUT1 transporters

44
Q

what happens in the early primal tubule

A

in the early primal tubule >90% of glucose is absorbed by SGLT2

45
Q

what happens in the late proximal tubule

A

In the late proximal tubule, almost all of the remaining glucose os absorbed by SGLT1

46
Q

in healthy conditions, how much filtered glucose is reabsorbed

A

> 99%

47
Q

what happens in people with diabetes to this level

A

the absorptive capacity of glucose transporters is overwhelmed in people with diabetes

48
Q

what do SGLT2 inhibitors promote

A

insulin loss and are used as diabetes therapy, pass out much more glucose in the urine

49
Q

what are two different diabetes therapy

A

K channel inhibitor
enhance insulin secreiton

50
Q

describe the uptake of glucose into the beta cells

A

Uptake via the GLUT1 and GLUT2

Metabolism

Leads to generation of signalling molecules such as ATP which stimulates the closure of potassium channels - located within the cell membrane

When these potassium channels are closed, this leads to depolarisation of the beta cell which leads to an influx of sodium and calcium into the cell via calcium channels

This influx of calcium leads to exocytosis - insulin release from the beta cell and into the blood stream

51
Q

what is the class of drugs used to counteract this

A

sulphinurias

52
Q

describe the GLP-1 mediated insulin release cascade

A

Activation of GLP-1 receptor

G protein stimulation

Stimulation of adenylate cyclase

Elevation of cAMP

Exocytosis

Activation of PKA and Epac2

53
Q

what diabetes therapies are used for this

A

incretin minetics
enhance insulin secretion

54
Q

what is the mechanism of action of the beta cells

A

Uptake
Metabolism
K ATP channel closure

Activation of GLP1 receptor
G protein stimulation
Stimulation of adenylate cyclase
Elevation of cAMP
Exocytosis
Activation of PKA and Epac2
Insulin release

55
Q

describe the process of insulin sensitive glucose transport

A

GLUT 4 :

Insulin binding to receptors
Tyrosine kinase actiivation
Signalling molecules: PRS, P13K, PDK1, AKT, AS160 etc
Translocate GLUT4 transporters
Glucose uptake

56
Q

what therapies are given for this signalling pathway

A

enhance insulin signalling e.g metformin

57
Q

where are the immediate effects of insulin

A

in the cytoplasm

58
Q

what does lower insulin lead to

A

increase glucose production and lowered peripheral glucose uptake
this leads to hyperglycaemia

59
Q

what is the short term complications of hyperglycaemia

A

Glucosuria leading to dehydration, polydipsia, osmotic diuresis
This short term problem leads to ketoacidosis

60
Q

what are the long term effects of hyperglycaemia

A

leads to diabetes complications

61
Q

where does glucotoxicity take place

A

capillary endothelial cells; mesangial cells; neurones and Schwann cells in peripheral nerve

Semester 4 (80 decks)

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