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chemistry > Glucose testing methods > Flashcards

Glucose testing methods Flashcards

1
Q

Metabolism of glucose (4)

A
  1. Converted to glycogen via glycogenesis & stored ( mainly in liver & muscle )
  2. Metabolized to CO2, H2O & energy via Tricarboxylic acid cycle, electron transport chain & Oxidative Phosphorylation
  3. Converted to ketoacids, amino acids & proteins ( transmission)
  4. Converted to fat & stored in adipose tissue as triglycerides ( via acetyl CoA)
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2
Q

Glycolysis

A

Metabolism of glucose to pyruvate or lactate for production of energy ( important for muscle tissue )

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3
Q

Glycogenolysis

A

Breakdown of glycogen to glucose for energy

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4
Q

Glycogenesis

A

Conversion of glucose to glycogen for storage

  • glucose can be used by the liver & other cells for energy or stored as glycogen for later use
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5
Q

Gluconeogeneisis

A

Formation of glucose from non carbohydrate sources

Ex. Conversion of amino acids by the liver

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6
Q

Lipogenesis

A

Conversion of carbohydrates to fatty acids

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7
Q

Lipolysis

A

Decomposition of fats

  • if glucose supply is low the liver can use glycogen ( lasts 12-16hrs) & other substrates to raise blood glucose concentration
    • glycerol from triglycerides
    • lactic acid from skin & muscle
    • amino acids
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8
Q

Hormonal control of glucose

A

Increase blood glucose

  • glucagon
  • Adrenalin ( Epinephrine)
  • glucocorticoids ( cortisol & cortisone )
  • growth hormone
  • adrenocorticotropic hormone ( ACTH)
  • thyroxine
  • somatostatin

Decreases blood glucose
- insulin

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9
Q

Glucagon

A

Primary hormone responsible for increasing glucose

Produced by alpha cells of islets of Langerhans in the pancreas

Released during stress & fasting states

Promotes glycogenolysis & gluconeogensis

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10
Q

Epinephrine

A

Aka adrenaline

Produced by adrenal medulla

Increases glucose production by:

  • inhibiting insulin secretion
  • increasing glycogenolysis ( breakdown of glycogen)
  • promoting lipolysis ( breakdown of fat )
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11
Q

Glucocorticoids

A

Primarily cortisol

Secreted by adrenal cortex when stimulated by ACTH

Increases plasma glucose by

  • decreasing intestinal entry into cell
  • increasing gluconeogenesis, liver glycogen & lipolysis
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12
Q

Growth hormone

A

Produced by anterior pituitary gland

Increases glucose production by:

  • decreasing entry of glucose into the cells
  • increasing glycolysis ( metabolism of glucose to pyruvate / lactate)
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13
Q

Adrenocorticotropic Hormone ( ACTH)

A

Produced by anterior pituitary gland

Increases release of cortisol

Increases plasma glucose by:

  • converting liver glycogen to glucose
  • promoting gluconeogenesis
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14
Q

Thyroxine

A

Produced by thyroid gland

Increases glucose production by :
- increasing glycogenolysis, gluconeogenesis & intestinal absorption of glucose

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15
Q

Somatosatin

A

Produced by the alpha- cells of the islets of Langerhans in the pancreas

Increases plasma glucose by :
- inhibiting insulin, glucagon & growth hormone

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16
Q

Insulin

A

Primary hormone responsible for decreasing glucose

Produced by beta - cells of islets of Langerhans
In the pancreas

Promotes the storage of glucose as glycogen

Promotes the formation of lipids from glucose

Increases the permeability of glucose to cell

17
Q

Theory of insulin action

A

Beta cells detect an increase in glucose, they release insulin
The insulin causes glucose to move into the cells ( muscle & adipose tissue ) via transport receptors Pg.98

18
Q

Sodium dependent glucose transporters

A

Promote uptake of glucose form lumen of the small bowel

Promote reabsorption of glucose from urine I’m the kidney

19
Q

Facilitative glucose transporters ( GLUTs)

A

Located on the surface of all cells

Designated GLUT1- GLUT14

Eleven mediate glucose transport

Divided into 3 subfamilies

  • class l ( GLUT1-4)
  • class ll ( GLUT 5,7,9,11)
  • class lll ( GLUT 6,8,10,12,14)
20
Q

GLUT 1&3

A

GLUT 1& 3 provide the glucose requirements of the brain

21
Q

GLUT 2 are found in

A

hepatocytes

B-cells of the pancreas

basolateral membranes of intimal & renal cells

allows the movement of glucose into & out of these cells

22
Q

GLUT 4

A

catalyzes a rate-limiting step for glucose uptake and metabolism in skeletal muscle
-skeletal muscle is the major organ of glucose consumption

when insulin concentration in the blood are low, GLUT 4 is localized in intracellular compartments & is inactive

insulin is released after a meal & stimulate the translocation of GLUT 4 to the plasma membrane
-this promotes uptake of glucose into skeletal muscle & fat

23
Q

measurement of blood glucose

A

serum, plasma, whole blood, urine, & CSF can be analyzed

serum & plasma should be separated from cells within 1 hour of collection

if delayed analysis, collect in sodium fluoride tube ( grey)
this will prevent glycolysis

fasting blood glucose tests should be performed in the morning after an 8 - 10 hour fast

  • higher in the morning than the afternoon ( diurnal)
  • diabetes may be missed in patients tested in afternoon
24
Q

glucose results based on sample type

A

serum& plasma values will be higher than whole blood values

venous whole blood ( lowest)
capillary/arterial
serum/plasma ( highest )

whole blood concentrations are approx. 10-12% lower than plasma

25
Q

methods for glucose testing

A

oxidation/reduction reaction methods

aromatic amines methods

enzymatic methods

  • glucose oxidase
  • hexokinase

electrode methods

26
Q

oxidation/reduction reaction- Copper Reduction

A

Cupric copper is reduced to cuprous copper by a reducing sugar ( glucose )

used in urinalysis ( clinitest)

( blue)                                                                (red)
  1. cuprous copper + reducing sugar ———> cuprous copper
  2. cuprous copper + Phosphomolybdic acid———————————>phosphomolybdous acid ( blue )

blue color measured using spectrophotometer and is related ti the sugar concentration

recorded as 1+ 2+ 3+ 4+

positive for all reducing sugars

used for determining genetic disorders
-ex. galactosemia
urine dipstick neg ( no glucose in urine)
urine flintiest pos ( galactose detected )

27
Q

glucose oxidase

A

most specific enzyme for glucose
only reacts with ß- D glucose

method:
glucose + O2—>Gluconic acid + H2O2
H2O2 + chromagen —> oxidized chromagen + H2O

chromagen is colorless until oxidized
conc of glucose is proportional to color

28
Q

what are 2 step reaction called

A

Trinder Reactions

29
Q

chromagens in glucose oxidase

A

chromogens are colourless chemical compounds that can be converted to a dye or color compound through a chemical reaction

o-dianisidine ( brown)

o-tolidine( blue)

4-aminophenizone( red) **

two other common chromogens:
3-methyl-2-benzothiazolinone hydrazone
N,N-Dimethylalaniine

30
Q

alpha & beta glucose

& what converts one to the other

A

Blood glucose :
alpha-D glucose ( 36%)
beta -D glucose ( 64%)

glucose oxidase can only cause oxidation of the Beta for,

Mutarotase can be added to convert alpha to beta forms
extend incubation time will allow spontaneous conversion

31
Q

interfering substances in glucose oxidase

A

in 2nd step other substances in the sample can be oxidized instead of the chromagen
- results in a decrease of color & a false decrease in glucose reading
other reducing substances :
uric acid
bilirubin
ascorbic acid ( vitamin C)
glutathione ( anti-oxidant)

a false increase in glucose conc. can be caused by strong oxidizing substances ( bleach )

32
Q

glucose oxidase -CSF

A

CSF glucose is a STAT ( freeze if cant do ASAP & freeze after)
CSF levels will be ~60% of blood glucose levels ( plasma )

reference range : 2.2-3.9 mol/L

decreased :

  • bacterial meningitis
  • fungal infection

increased :

  • hyperglycaemia
  • traumatic tap
33
Q

whats in the glucose reagent

A

BUFFER

NOT GLUCOSE

34
Q

what is the reference method for glucose

A

Hexokinase

  • more accurate than glucose oxidase
  • less interferences ( not affected by uric acid & ascorbic acid )
  • can be performed on serum, plasma , urine, CSF &serous fluid
35
Q

what causes a false decrease in hexokinase results

A

grosss hemolysis & very high bilirubin

36
Q

steps of hexokinase

A

Glucose + ATP –> glucose- 6-phosphate + ADP

G-6-P + NADP+ —-> 6- phosphogluconate + NADPH + H+

NADP+ no absorbance at 340 nm
NADPH absorbance at 340 nm

increase in absorbance is read @ 340 nm

37
Q

enzymatic methods- Glucose dehydrogenase

A

Glucose + NAD+ —-> Gluconolactone + NAD + H+

increased absorbance at 340 nm( form NADH) is measured

NADH generated is proportional to glucose conc
not widely used

38
Q

polarographic electrode methode ( oxygen electrode)

A

measures the rate of oxygen consumption ( depletion ) after sample is added to a solution containing glucose oxidase

glucose + O2 –> gluconic acid + H2O2

H2O2 needs to be eliminated through two side reactions with catalase & molybdate ( to prevent the reaction from reversing )

suitable for serum, plasma & CSF

NOT WHOLE BLOOD ( blood cells consume oxygen)

chemistry (13 decks)

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