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BRS - Endo > Glucose Homeostasis > Flashcards

Glucose Homeostasis Flashcards

1
Q

Why is glucose important?

A

important as energy substrate, especially for cns

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2
Q

What are normal levels of blood glucose conc. for an adult?

A

4-5 mmol/L

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3
Q

What happens to the CNS when normal blood glucose levels fall?

A

cerebral function is increasingly impaired

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4
Q

What happens when blood glucose conc. falls under 2 mmol/L?

A

unconsciousness, coma, death

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5
Q

What kind of structure does the pancreas have?

A

retroperitoneal - has the peritoneum on the anterior side only

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6
Q

Are the pancreas secretions mainly exocrine or endocrine?

A

98% exocrine secretions via duct to the small intestines

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7
Q

What are the Islets of Langerhans?

A

small clumps of cells that make up 2% of pancreatic tissue

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8
Q

What are the 3 different types of cells in the Islets? What do they produce?

A

α cells ➜ GLUCAGON
ß cells ➜ INSULIN
δ cells ➜ SOMATOSTATIN

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9
Q

How do the cells of the Islets comunicate?

A

paracrine communication

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10
Q

What are the “gap junctions” in the Islets?

A

allow small molecules to pass directly between cells

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11
Q

What are the “tight junctions” in the Islets?

A

create small intercellular spaces

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12
Q

What is the general function of insulin?

A

decreases blood glucose + stimulates growth and development

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13
Q

What is the general function of glucagon?

A

increases blood glucose

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14
Q

What is the general function of somatostatin (in gluco homeo)?

A

inhibits insulin and glucagon

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15
Q

What processes increase/decrease due to insulin?

A 
↑ glycogenesis
↑ glycolysis
↑ glucose transport into cells via GLUT4
↑ amino acid transport
↑ protein synthesis
↑ lipogenesis
↓ lipolysis
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16
Q

What processes increase/decrease due to glucagon?

A

↑ amino acid transport into liver for gluconeogensis
↑ gluconeogenesis
↑ lipolysis for gluconeogenesis
↑ hepatic glycogenolysis

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17
Q

What stimulates beta cells to release insulin?

A

certain AAs, GI hormones, PNS activity, SNS activity to ß-receptors, glucagon release AND increase in plasma blood glucose

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18
Q

What inhibits insulin release from beta cells?

A

certain SNS activity via α-receptors + somatostatin release

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19
Q

What stimulates alpha cells to release glucagon?

A

certain AAs, GI hormones, PNS activity, SNS activity to α-receptors, AND decrease in plasma blood glucose

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20
Q

What inhibits glucagon release from alpha cells?

A

insulin and somatostatin release

21
Q

What glucose transporters do beta cells use?

A

GLUT2

22
Q

What is the main glucose sensor of the Islets?

A

Glucokinase (hexokinase IV) - not GLUT2 because it’s insulin independent
- glucokinase is the rate-limiting step of glycolysis

23
Q

What is the mechanism of insulin release?

A
  • high glucose plasma levels = beta cell uptake of glucose
  • cell metabolism = increase in ATP
  • ATP inhibits voltage gated K+ channels
  • depolarisation of cell membrane = Ca gates open
  • influx of Ca ions = exocytosis of insulin vesicles
24
Q

What is proinsulin?

A

inactive precursor for insulin, A-chain + C-peptide + B-chain

25
Q

What is C-peptide?

A

short 31 AA polypeptide, connects insulin’s A-chain to its B-chain in proinsulin molecule, removed by proteolytic cleavage

26
Q

Why is C-peptide clinically important?

A

measured as a surrogate marker for insulin:

  • insulin is difficult to measure
  • c-peptide : insulin is 1 : 1
27
Q

What is an incretin?

A

group of metabolic GI hormones that stimulate decrease in blood glucose levels by stimulating insulin release from beta cells

28
Q

What is GLP-1?

A

GI hormone, an incretin secreted in response to nutrients in gut (transcription product of pro-glucagon gene, mostly from L-cell)

30
Q

What does GLP-1 stand for?

A

glucagon like peptide - 1

31
Q

What is the function of GLP-1?

A

Stimulates insulin, suppresses glucagon, ↑ satiety (feeling of ‘fullness’)

32
Q

What is the half life of GLP-1 like?

A

Short half life due to rapid degradation from enzyme dipeptidyl peptidase-4 (DPPG-4 inhibitor)

33
Q

What is the clinical important of GLP-1?

A

Used in treatment of diabetes mellitus

34
Q

What are GLUT receptors?

A

glucose transporters, facilitated diffusion

34
Q

What are SGLT1 and SGLT2?

A

Glucose transporters for the luminal epithelial cells in the kidney + small intestine, uses active transport

35
Q

Where is GLUT-1 found?

A

endothelium, erythrocytes (RBCs)

36
Q

What is the function of GLUT-1?

A

basal transport (insulin independent)

37
Q

Where is GLUT-2 found?

A

kidney, small intestine, liver, pancreatic beta cells

38
Q

What is the function of GLUT-2?

A

low affinity, high capacity transport (insulin independent)

39
Q

Where is GLUT-3 found?

A

neurones, placenta

40
Q

What is the function of GLUT-3?

A

high affinity transport (insulin independent)

41
Q

Where is GLUT-4 found?

A

skeletal muscle, adipose

42
Q

What is the function of GLUT-4?

A

insulin-regulated glucose transport

43
Q

What is an insulin receptor?

A

receptor for insulin in adipocytes and myocytes to stimulate glucose uptake through GLUT-4

44
Q

How does the insulin receptor work?

A

insulin binds to α-subunits, ➜ causes a conformational change in the tyrosine
kinase domains of the b-subunits
➜ triggers a cascade of protein reactions that result in GLUT-4 vesicle to fuse w/ membrane so glucose can be taken in

45
Q

What is the basic structure of an insulin receptor?

A

2 α-subunits + 2 ß-subunits

46
Q

How many phases is insulin released in?

A

2 phases

47
Q

What is FPIR?

A

First Phase Insulin Release - insulin stored in pancreas is released immediately after a meal, lasts for 10-15 mins, prevents steep plasma glucose increase

48
Q

What disorder means that FPIR doesn’t happen?

A

Type 2 diabetes mellitus

BRS - Endo (9 decks)

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