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brs (phase 1a) > (endo) glucose homeostasis > Flashcards

(endo) glucose homeostasis Flashcards

1
Q

what blood glucose concentration classifies as hypoglycaemia?

A

when blood glucose levels fall below 4-5 mmol/L
= hypoglycaemia
= cerebral function increasingly impaired

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2
Q

what happens if blood glucose levels are <2 mmol/L?

A

coma & untimely death can result

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3
Q

why is persistent hyperglycaemia bad?

A

can result in diabetes mellitus

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4
Q

which hormones act to increase blood glucose levels?

A

glucagon

cortisol
GH
catecholamines

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5
Q

which hormones act to decrease blood glucose levels?

A

insulin

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6
Q

what are the phenotypes of diabetes mellitus?

A

1) type 1 diabetes mellitus
2) type 2 diabetes mellitus
3) maturity-onset diabetes of the young (MODY)

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7
Q

what two types of cells are found in the pancreas?

A

1) exocrine acinar cells (98%)

2) islets of Langerhans (2%)

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8
Q

name the islet cells of the pancreas

A

1) alpha cells (glucagon)
2) beta cells (insulin)
3) delta cells (somatostatin)

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9
Q

what type of intercellular communication occurs between islet cells in the pancreas?

A

paracrine communication

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10
Q

how is paracrine communication enabled between islet cells of the pancreas?

A

via

1) gap junctions = allow small molecules to pass bw cells directly
2) tight junctions = create small intercellular spaces

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11
Q

what do alpha islet cells of the pancreas secrete?

A

glucagon

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12
Q

what do beta islet cells of the pancreas secrete?

A

insulin

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13
Q

what do gamma islet cells of the pancreas secrete?

A

somatostatin

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14
Q

what is the function of insulin?

A

1) reduce blood glucose

2) stimulate growth and development

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15
Q

what is the function of glucagon?

A

increases blood glucose levels

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16
Q

how does the body respond primarily to an increased blood glucose level?

A

increased blood glucose
= increased stimulation of pancreatic beta cells
= increased insulin secretion

17
Q

besides an increased blood glucose level, what also stimulates insulin secretion from beta cells?

A

1) some amino acids, GI hormones
2) SNS activity (via beta pathways)
3) PNS activity
4) glucagon from pancreatic alpha cells

18
Q

what inhibits insulin secretion from beta cells?

A

1) SNS activity (via alpha pathways)

2) somatostatin from pancreatic delta cells

19
Q

how does insulin act to reduce blood glucose levels?

A

1) increased glycogenesis, glycolysis and increased uptake of glucose via GLUT4 receptors
2) increased amino acid transport, increased protein synthesis
3) increased lipogenesis (reduced lipolysis)

20
Q

how does the body respond primarily to an reduced blood glucose level?

A

reduced blood glucose levels
= increased stimulation of alpha cells
= increased glucagon secretion

21
Q

besides a reduced blood glucose level, what also stimulates glucagon secretion from alpha cells?

A

1) some amino acids, GI hormones
2) SNS activity (via alpha pathways)
3) PNS activity

22
Q

what inhibits glucagon secretion from alpha cells?

A

1) insulin from pancreatic beta cells

2) somatostatin from pancreatic delta cells

23
Q

how does glucagon act to reduce blood glucose levels?

A

1) increased hepatic glycogenolysis
2) increased proteolysis and amino acid transport to the liver = gluconeogenesis
3) increased lipolysis = gluconeogenesis

24
Q

what is thought to be the main glucose sensor in beta cells?

A

glucokinase

i.e. hexokinase IV

25
Q

explain the process by which insulin secretion from pancreatic beta cells is controlled

(when blood glucose is high)

A

increased blood glucose concentration
= increased glucose uptake into beta cells via GLUT2 channels
= increased conversion of glucose to G6P via glucokinase
= reduced ATP (and increased ADP)
= reduced activation of ATP-sensitive K+ channels so they remian closed
= intracellula K+ conc remains high
= increased activation of Ca2+ channels
= increased intracellular Ca2+ influx
= stimulates increased insulin secretion into the bloodstream

26
Q

how is proinsulin converted into insulin?

A

proinsulin undergoes proteolytic cleavage into insulin

27
Q

compare the structure of proinsulin and insulin

A

proinsulin = A chain + B chain + C-peptide

insulin = just A chain + B-chain (the C-=peptide is cleaved off)

28
Q

a healthy person eats a Big Mac meal

what would you expect to happen to their C-peptide?

A

increases

29
Q

a person with Type 1 diabetes mellitus eats a Big Mac meal

what do you expect their C-peptide to be?

A

should increase but stays LOW

30
Q

what is the gastrointestinal ‘incretin’ effect?

A

when glucose is taken orally rather then intravenously
= in response to the nutrient ingestion, incretin is released
= stimulates insulin secretion even more

= higher plasma insulin levels are seen after an oral glucose load rather than an IV glucose load

31
Q

what is GLP-1?

A

a gut hormone secreted in response to nutrients in the gut

= stimulates insulin, inhibits glucagon

32
Q

what is the function of GLP-1?

A

1) stimulates insulin, suppresses glucagon

2) promotes satiety (‘fullness’)

33
Q

from where is GLP-1 secreted?

A

mainly L cells

short half life due to DPP-4 enzyme

34
Q

why is GLP-1 important?

A

used in the treatment of diabetes

= DPP-4 inhibitor will delay the degradation of GLP-1 so it remains within circulation longer to increase insulin secretion and keep glucagon secretion suppressed

35
Q

what is first-phase insulin release?

A

the initial burst of insulin, which is released in the first 5–10 min after the β-cell is exposed to a rapid increase in glucose

36
Q

how does the first-phase insulin release compare in a healthy person and one who has T2DM?

A

healthy = huge burst of insulin released in the first 10 mins following glucose increase

T2DM = the increase in insulin is not as larger or rapid

37
Q

what does insulin bind to?

A 
insulin receptor
(extracellular domain)
38
Q

what is the structure of the insulin receptor?

A

1) alpha subunit (extracellular)

2) beta subunit (through cell membrane + and intracellular)

39
Q

what occurs once insulin binds to its receptor?

A

insulin binds to the extracellular alpha subunit of the insulin receptor

= binding causes a conformational shape change in the tyrosine kinase domains of the beta subunits

brs (phase 1a) (7 decks)

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