Glucose testing methods

Question 1

Metabolism of glucose (4)

Answer 1

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)

Question 2

Glycolysis

Answer 2

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

Question 3

Glycogenolysis

Answer 3

Breakdown of glycogen to glucose for energy

Question 4

Glycogenesis

Answer 4

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

Question 5

Gluconeogeneisis

Answer 5

Formation of glucose from non carbohydrate sources

Ex. Conversion of amino acids by the liver

Question 6

Lipogenesis

Answer 6

Conversion of carbohydrates to fatty acids

Question 7

Lipolysis

Answer 7

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

Question 8

Hormonal control of glucose

Answer 8

Increase blood glucose

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

Decreases blood glucose
- insulin

Question 9

Glucagon

Answer 9

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

Question 10

Epinephrine

Answer 10

Aka adrenaline

Produced by adrenal medulla

Increases glucose production by:

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

Question 11

Glucocorticoids

Answer 11

Primarily cortisol

Secreted by adrenal cortex when stimulated by ACTH

Increases plasma glucose by

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

Question 12

Growth hormone

Answer 12

Produced by anterior pituitary gland

Increases glucose production by:

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

Question 13

Adrenocorticotropic Hormone ( ACTH)

Answer 13

Produced by anterior pituitary gland

Increases release of cortisol

Increases plasma glucose by:

• converting liver glycogen to glucose
• promoting gluconeogenesis

Question 14

Thyroxine

Answer 14

Produced by thyroid gland

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

Question 15

Somatosatin

Answer 15

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

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

Question 16

Insulin

Answer 16

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

Question 17

Theory of insulin action

Answer 17

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

Question 18

Sodium dependent glucose transporters

Answer 18

Promote uptake of glucose form lumen of the small bowel

Promote reabsorption of glucose from urine I’m the kidney

Question 19

Facilitative glucose transporters ( GLUTs)

Answer 19

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)

Question 20

GLUT 1&3

Answer 20

GLUT 1& 3 provide the glucose requirements of the brain

Question 21

GLUT 2 are found in

Answer 21

hepatocytes

B-cells of the pancreas

basolateral membranes of intimal & renal cells

allows the movement of glucose into & out of these cells

Question 22

GLUT 4

Answer 22

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

Question 23

measurement of blood glucose

Answer 23

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

Question 24

glucose results based on sample type

Answer 24

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

Question 25

methods for glucose testing

Answer 25

oxidation/reduction reaction methods aromatic amines methods enzymatic methods - glucose oxidase - hexokinase electrode methods

Question 26

oxidation/reduction reaction- Copper Reduction

Answer 26

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 )

Question 27

glucose oxidase

Answer 27

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

Question 28

what are 2 step reaction called

Answer 28

Trinder Reactions

Question 29

chromagens in glucose oxidase

Answer 29

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

Question 30

alpha & beta glucose | & what converts one to the other

Answer 30

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

Question 31

interfering substances in glucose oxidase

Answer 31

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 )

Question 32

glucose oxidase -CSF

Answer 32

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

Question 33

whats in the glucose reagent

Answer 33

BUFFER | NOT GLUCOSE

Question 34

what is the reference method for glucose

Answer 34

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

Question 35

what causes a false decrease in hexokinase results

Answer 35

grosss hemolysis & very high bilirubin

Question 36

steps of hexokinase

Answer 36

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

Question 37

enzymatic methods- Glucose dehydrogenase

Answer 37

Glucose + NAD+ ----> Gluconolactone + NAD + H+ increased absorbance at 340 nm( form NADH) is measured NADH generated is proportional to glucose conc not widely used

Question 38

polarographic electrode methode ( oxygen electrode)

Answer 38

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)