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Nutritional Physiology > Glucose Metabolism, Diabetes & Starvation > Flashcards

Glucose Metabolism, Diabetes & Starvation Flashcards

1
Q

What are the monosaccharides?

A

Glucose, galactose and fructose

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2
Q

What are the disaccharides?

A

Sucrose (Gl and Fr), lactose (Gl and Ga), maltose (Gl and Gl)

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3
Q

What are the polysaccharides?

A

Starch and cellulose

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4
Q

What supply of glucose does the brain need?

A

0.5mM/min

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5
Q

Low blood glucose=

A

Coma

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6
Q

High blood glucose=

A

Glycosylation of proteins

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7
Q

Islets of Langerhans

A
  • diameter= 1mm
  • 1 million present in each pancreas
  • 4 cell types: a, b, d, f
  • B cells = 75%
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8
Q

What stimulates the release of insulin?

A

Glucose
Amino acids (especially alanine)
Glucagon

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9
Q

What inhibits insulin secretion?

A

Somatostatin

Sympathetics

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10
Q

What is insulin?

A

Preproinsulin translational products

24aa

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11
Q

What is the cleaving process of preproinsulin?

A
  • occurs in trans Golgi

- packages into secretory granules and proteases cleave at 2 sites

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12
Q

What are the products of cleaved preproinsulin?

A

2 peptide chains:

  1. Insulin (A-21Aa, B: 30aa)
  2. C-peptide (31aa)
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13
Q

How does glucose increase the secretion of insulin? (5)

A
  1. GLUT2 transporter
  2. Glycolysis generates ATP
  3. ATP sensitive K+ channel activated : the more glucose, the more it is activated. Channel closes and K+ build up cases depolarisation
  4. Opens voltage gated Ca2+ channels
  5. When IC Ca2+ increases, vesicle release is stimulated
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14
Q

…. percent of insulin is cleared by the liver on the first pass

A

60

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15
Q

What is used to indicate B-cell function?

A

Circulating C-peptide

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16
Q

Insulin receptors characteristics

A
  • 2 extracellular alpha chains
  • 2 intracellular beta chains
  • beta chains have tyrosine kinase activity
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17
Q

What are the targets of insulin?

A
  • liver
  • skeletal muscle
  • adipose tissue
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18
Q

What are the risk factors for diabetes? (Type 2)

A
  • age: >40 years
  • family history
  • ethnicity
  • obesity
  • lack of exercise (exercise increases muscle glucose uptake independent of insulin)
  • hypertension, hyperlipidemia
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19
Q

What are the effects of insulin in the liver?

A
  1. GLUT2 transporter - not insulin dependent
  2. Promotes glycogenesis, inhibits glycogenolysis
  3. Promotes glycolysis and inhibits gluconeogenesis
  4. Promotes Limoges is
  5. Promotes protein deposition
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20
Q

What are the effects of insulin in the skeletal muscle?

A
  1. GLUT4 is insulin dependent and recruited to cell membrane
  2. Promotes glycogenesis, inhibits glycogenolysis
  3. Promotes glycolysis
  4. Promotes protein deposition and inhibits protein breakdown (maintains muscle mass)
21
Q

What are the effects of insulin in the adipose tissue?

A
  1. GLUT4 is insulin dependent and recruited to cell membrane
  2. Promotes glycolysis and shuttling of PEP to glycerol and AcetylCoA to FFA
  3. Promotes uptake of FFAs from VLDL (via lipoprotein lipase expression)
  4. Inhibits hormone sensitive lipase (breaks down TGs)

= lowers blood glucose, stores energy as triglycerides

22
Q

Free glucose energy stores

A

Amount: 12g
Energy (MJ): 0.2
Supply: 30min

23
Q

Glycogen energy stores

A

Amount: 450g
Energy (MJ): 7.7
Supply: 18h

24
Q

Triacyglycerol energy stores

A

Amount: 15kg
Energy (MJ): 550
Supply: 55d

25
Q

Protein energy stores

A

Amount: 15kg
Energy (MJ): 550
Supply: 21d

26
Q

What happens initially in short term fasting?

A
  • decrease plasma glucose
  • decrease insulin
  • increase glucagon
27
Q

What stimulates glucagon secretion from alpha cells?

A
  • decrease in glucose

- increase in amino acids (especially alanine - prevents hypoglycaemia in response to a pure protein meal)

28
Q

In fasting:

A
  • main target of glucagon is the liver
  • all the things that insulin stimulates are reduced
  • glucagon often stimulates reverse pathway
29
Q

What does glucagon do in the liver?

A
  • inhibits glycogenesis
  • promotes glycogenolysis
  • glucose is formed from glycogen (via glucose-6-phosphatase) and released into the blood
30
Q

Glucagon: liver vs muscle

A
  • glucose-6-phosphatase is not present in skeletal muscle

- muscle uses stores but doesn’t release into bloodstream

31
Q

Glycogen in liver

A

Amount: 100g
Energy (MJ): 1.7
Supply: 4h

32
Q

Glycogen in muscle

A

Amount: 350g
Energy (MJ): 6
Supply: 14h

33
Q

Glycogen reserves in starvation are exhausted after……

A

A single day

34
Q

What are the problems and solutions of using fat as our biggest energy store?

A

Problems

  • not all tissues oxidise FFAs
  • still require non-fat sources

Solutions

  • gluconeogenesis
  • ketone body metabolism
35
Q

Where are the 3 carbon substrates for glucose creation found?

A
  • lactate
  • pyruvate
  • AAs
  • glycerol

NOT FFAs

36
Q

Gluconeogenesis requires energy from……. for…….

A

Fat for resynthesis of NAD+

37
Q

What are the effects of glucagon in the liver?

A
  1. Inhibits glycolysis
  2. Promotes gluconeogenesis
  3. Glucose made from amino acids is then available for use by the body
38
Q

What happens in adipose tissue during fasting?

A
  1. Triglycerols are mobilised

2. Results in release of non-esterified fatty acids (NEFA)

39
Q

In starvation, muscles use mostly ….. for fuel

A

Fats, not glucose

40
Q

What effects does glucagon have in the liver in terms of fats?

A
  • FFAs are enzymatically broken down by beta-oxidation to form Acetyl CoA
  • the liver produces large amounts of ketone bodies from this
  • promotes lipolysis, FA oxidation
  • inhibits lipogenesis
41
Q

What are the ketone bodies?

A
  • acetoacetate
  • beta-hydroxybutyrate
  • acetone (minor)
42
Q

Ketone bodies are taken up by ………, especially the …….

A

Other tissues, the brain

43
Q

What happens when ketone bodies are uptakes by cells?

A
  • converted back to AcetylCoA

- oxidised via citric acid cycle to produce ATP

44
Q

Ketone production is ‘…….. …….’, as it helps minimise muscle breakdown

A

Muscle sparing

45
Q

What is the timeline of fasting/starvation?

A
  • stop eating
  • insulin decreases, glucagon increases
  • liver glycogen depleted (18hrs)
  • plasma glucose decreases, NEFA increases
  • tissues switch to FA metabolism
  • liver gluconeogenesis and ketone production
  • general metabolism decreases - T3 decreases
46
Q

What is the total number of days you can survive without food?

A

77

47
Q

What usually causes death after starvation?

A
  • heart attack
  • renal failure
  • muscle weakness (diaphragm) leading to pneumonia
48
Q

What happens during long term starvation? (5)

A
  1. Body reaches a kind of steady state
  2. There is a gradual depletion of body protein and steady depletion of fat stores
  3. Blood ketones reach 6-8mmol/L, brain uses 2/3 of ketones
  4. Some other tissues use glucose but release lactate, which is recycled to glucose by the liver using energy from FFAs
  5. Essential vitamins such as B-group vitamins and vitamin C are short lived, and severe deficiencies occur after a few weeks

Nutritional Physiology (13 decks)

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