포도당 glucose

[진성]

Glucose (포도당)

Preferred IUPAC name[hide] D-Glucose
Systematic name[hide] (2R,3S,4R,5R)-2,3,4,5,6-Pentahydroxyhexanal
Other names[hide] Blood sugar Dextrose Corn sugar D-Glucose Grape sugar
Identifiers
Abbreviations	Glc
CAS number	50-99-7 Y
PubChem	5793
ChemSpider	5589 Y
UNII	5SL0G7R0OK Y
EC number	200-075-1
KEGG	C00031 N
MeSH	Glucose
ChEBI	CHEBI:4167 Y
ChEMBL	CHEMBL1222250 Y
RTECS number	LZ6600000
ATC code	B05CX01,V04CA02, V06DC01
Beilstein Reference	1281604
Gmelin Reference	83256
3DMet	B04623
Jmol-3D images	Image 1 Image 2
·
Properties
Molecular formula	C6H12O6
Molar mass	180.16 g mol−1
Appearance	White powder
Density	1.54 g/cm3
Melting point	α-D-glucose: 146 °C β-D-glucose: 150 °C
Solubility in water	90.9 g/100 mL (25 °C)
Thermochemistry
Specific heat capacity C	218.6 J K−1 mol−1[1]
Std molar entropy So298	209.2 J K−1 mol−1[1]
Std enthalpy of formation ΔfHo298	−1271 kJ/mol [2]
Std enthalpy of combustion ΔcHo298	−2805 kJ/mol
Hazards
MSDS	ICSC 0865
EU Index	not listed

Glucose (C₆H₁₂O₆, also known as D-glucose, dextrose, or grape sugar)

is a simple aldosic monosaccharide found in plants.

It is one of the three dietary monosaccharides,

along with fructose and galactose,^{[citation needed]}

that are absorbed directly into the bloodstream during digestion.

It is an important carbohydrate in biology, which is indicated by the fact that cells use it

as a secondary source of energy and a metabolic intermediate.

Glucose is one of the main products of photosynthesis and fuels for cellular respiration.

Glucose exists in several different molecular structures,

but all of these structures can be divided into two families of mirror-images (stereoisomers).

Only one set of these isomers exists in nature, those derived from the particular chiral form

of glucose that is denoted D-glucose, or D-glucose.

The chemical D-glucose is sometimes referred to as dextrose,

a historical name that derives from dextrorotatory glucose because a solution of D-glucose in water

rotates the plane of polarized light to the right (dextro).^[3]

However, the D- in D-glucose refers to a chiral chemical similarity property in sugars,

not the property of rotating light (for example, D-fructose rotates light to the left).

For this reason, the D- and L- designations in sugars do not perfectly predict optical rotation,

and do not refer to this property.

Starch and cellulose are polymers derived from the dehydration of D-glucose.

The other stereoisomer, called L-glucose, is rarely found in nature.

The name "glucose" comes from the Greek word γλευχος, meaning "sweet wine, must".^[4]

The suffix "-ose" denotes a sugar.

Function [edit]

Why glucose — and not another monosaccharide such as fructose

— is so widely used in organisms is not clearly understood.^{[citation needed]}

One reason might be that glucose has a lower tendency than other hexose sugars to

react non-specifically with the amino groups of proteins.

This reaction - (glycation) - reduces or destroys the function of many enzymes.

The low rate of glycation is due to glucose's preference for the less reactive cyclic isomer.

Nevertheless, many of the long-term complications of diabetes

(e.g., blindness, renal failure, and peripheral neuropathy)

are probably due to the glycation of proteins or lipids.^[5]

In contrast, enzyme-regulated addition of glucose to proteins by glycosylation is often essential to

their function.

Another reason as to why glucose is the most common sugar is that

it is the most conformationally stable compared to other possibilities.

Analyte in medical blood test [edit]

Main article: Glucose test

Glucose is a common medical analyte measured in blood samples.

Eating or fasting prior to taking a blood sample has an effect on the result.

A high fasting glucose blood sugar level may be a sign of prediabetes or diabetes mellitus.

Energy source [edit]

Glucose is a ubiquitous fuel in biology.

It is used as an energy source in most organisms, from bacteria to humans.

Use of glucose may be by either aerobic respiration, anaerobic respiration, or fermentation.

Glucose is the human body's key source of energy, through aerobic respiration,

providing about 3.75 kilocalories (16 kilojoules) of food energy per gram.^[6]

Breakdown of carbohydrates (e.g. starch) yields mono- and disaccharides,

most of which is glucose.

Through glycolysis and later in the reactions of the citric acid cycle, glucose is oxidized to

eventually form CO₂ and water, yielding energy sources, mostly in the form of ATP.

The insulin reaction, and other mechanisms, regulate the concentration of glucose in the blood.

Glucose is a primary source of energy for the brain,

so its availability influences psychological processes.

When glucose is low, psychological processes requiring mental effort

(e.g., self-control, effortful decision-making) are impaired.^{[7][8][9][10]}

Glycolysis [edit]

α-D-Glucose	Hexokinase		α-D-Glucose-6-phosphate
	ATP	ADP

  

Glucose metabolism and various forms of it in the process

Glucose-containing compounds and isomeric forms are digested and taken up by the body in the

Intestines, including starch, glycogen, disaccharides and monosaccharides.

 

Glucose is stored in mainly the liver and muscles as glycogen.

 

It is distributed and used in tissues as free glucose.

Use of glucose as an energy source in cells is by aerobic respiration or anaerobic respiration.

Both start with the early steps of the glycolysis metabolic pathway.

The first step of this is the phosphorylation of glucose by hexokinase to prepare it for later

breakdown to provide energy.

The major reason for the immediate phosphorylation of glucose by a hexokinase is to prevent

diffusion out of the cell.

The phosphorylation 인산화 adds a charged phosphate group so the glucose 6-phosphate

cannot easily cross the cell membrane.

Irreversible first steps of a metabolic pathway are common for regulatory purposes.

In anaerobic respiration 무산소호흡,

one glucose molecule produces a net gain of two ATP molecules

(four ATP molecules are produced during glycolysis,

but two are required by enzymes used during the process).^[11]

In aerobic respiration 유산소호흡,

a molecule of glucose is much more profitable in that a net worth of 32 ATP molecules is generated

(34 gross with two being required in the process).^[12]

Click on genes, proteins and metabolites below to link to respective articles. ^{[§ 1]}

 Precursor [edit]

Organisms use glucose as a precursor for the synthesis of several important substances.

Starch, cellulose, and glycogen ("animal starch") are common glucose polymers (polysaccharides).

Some of these polymers (starch or glycogen) serve as energy stores,

while others (cellulose and chitin, which is made from a derivative of glucose) have structural roles.

Oligosaccharides of glucose combined with other sugars serve as important energy stores.

These include lactose, the predominant sugar in milk, which is a glucose-galactose disaccharide,

and sucrose, another disaccharide of glucose and fructose.

Glucose is also added onto certain proteins and lipids in a process called glycosylation.

This is often critical for their functioning.

[[ [[

]] Glycolysis and Gluconeogenesis edit

The enzymes that join glucose to other molecules usually use phosphorylated glucose to power

the formation of the new bond by breaking the glucose-phosphate bond.

Other than its direct use as a monomer, glucose can be broken down to synthesize a wide variety

of other biomolecules.

This is important,

as glucose serves both as a primary store of energy and as a source of organic carbon.

Glucose can be broken down and converted into lipids.

It is also a precursor for the synthesis of other important molecules such as vitamin C

(ascorbic acid).

Though plants and some microbes can create all the compounds they need from glucose given the

necessary minerals, animals and many microbes cannot synthesize the necessary compounds and

thus have to obtain them from an external source, such as diet.

1.       Jump up ^ The interactive pathway map can be edited at WikiPathways: "GlycolysisGluconeogenesis_WP534". 

Structure and nomenclature [edit]

Glucose is a monosaccharide with formula C₆H₁₂O₆ or H-(C=O)-(CHOH)₅-H,

whose five hydroxyl (OH) groups are arranged in a specific way along its six-carbon backbone.

Open-chain form [edit]

 

Glucose can exist in both a straight-chain and ring form.

D-Glucose in Fischer projection

In its fleeting open-chain form, the glucose molecule has an open (as opposed to cyclic)

and unbranched backbone of six carbon atoms, C-1 through C-6;

where C-1 is part of an aldehyde group H(C=O)-,

and each of the other five carbons bears one hydroxyl group -OH.

The remaining bonds of the backbone carbons are satisfied by hydrogen atoms -H.

Therefore glucose is a hexose and an aldose, or an aldohexose.

The aldehyde group makes glucose a reducing sugar giving a positive reaction with the

Fehling test.

Each of the four carbons C-2 through C-5 is a stereocenter,

meaning that its four bonds connect to four different substitutents.

(Carbon C-2, for example, connects to -(C=O)H, -OH, -H, and -(CHOH)₄H.)

In D-glucose, these four parts must be in a specific three-dimensional arrangement.

Namely, when the molecule is drawn in the Fischer projection, the hydroxyls on C-2, C-4,

and C-5 must be on the right side, while that on C-3 must be on the left side.

The positions of those four hydroxyls are exactly reversed in the Fischer diagram of L-glucose.

D- and L-glucose are two of the 16 possible aldohexoses; the other 14 are allose, altrose,

mannose, gulose, idose, galactose, and talose, each with two enantiomers, "D-" and "L-".

The aldehyde form of glucose

Cyclic forms [edit]

In solutions, the open-chain form of glucose (either "D-" or "L-") exists in equilibrium with several

cyclic isomers, each containing a ring of carbons closed by one oxygen atom.

In aqueous solution however, more than 99% of glucose molecules, at any given time,

exist as pyranose.

The open-chain form is limited to about 0.25% and furanose exists in negligible amounts.

The terms "glucose" and "D-glucose" are generally used for these cyclic forms as well.

The ring arises from the open-chain form by a nucleophilic addition reaction between

the aldehyde group  -(C=O)H   at C-1 and the hydroxyl group -OH at C-4 or C-5,

yielding a hemiacetal group -C(OH)H-O-.

The reaction between C-1 and C-5 creates a molecule with a six-membered ring, called pyranose,

after the cyclic ether pyran, the simplest molecule with the same carbon-oxygen ring.

The (much rarer) reaction between C-1 and C-4 creates a molecule with a five-membered ring,

called furanose, after the cyclic ether furan.

In either case, each carbon in the ring has one hydrogen and one hydroxyl attached,

except for the last carbon (C-4 or C-5) where the hydroxyl is replaced by the remainder of

the open molecule (which is -(C(CH₂OH)HOH)-H or -(CHOH)-H, respectively).

The ring-closing reaction makes carbon C-1 chiral, too, since its four bonds lead to -H, to -OH,

to carbon C-2, and to the ring oxygen.

These four parts of the molecule may be arranged around C-1 (the anomeric carbon)

in two distinct ways, designated by the prefixes "α-" and "β-".

When a glucopyranose molecule is drawn in the Haworth projection, the designation "α-" means

that the hydroxyl group attached to C-1 and the -CH₂OH group at C-5 lies on opposite sides of

the ring's plane (a trans arrangement), while "β-" means that they are on the same side of the

plane (a cis arrangement).

Therefore, the open-chain isomer D-glucose gives rise to four distinct cyclic isomers:

α-D-glucopyranose, β-D-glucopyranose, α-D-glucofuranose, and β-D-glucofuranose.

These are all chiral.

α-D- Glucopyranose

β-D- Glucopyranose

α-D- Glucofuranose

β-D- Glucofuranose

The other open-chain isomer L-glucose similarly gives rise to four distinct cyclic forms of L-glucose,

each the mirror image of the corresponding D-glucose.

The rings are not planar but twisted in three dimensions.

The glucopyranose ring (α or β) can assume several non-planar shapes,

analogous to the "chair" and "boat" conformations of cyclohexane.

Similarly, the glucofuranose ring may assume several shapes,

analogous to the "envelope" conformations of cyclopentane.

The glucopyranose forms of glucose predominate in solution,

and are the only forms observed in the solid state.

They are crystalline colorless solids, highly soluble in water and acetic acid,

poorly soluble in methanol and ethanol.

They melt at 146 °C (295 °F) (α) and 150 °C (302 °F) (β),

and decompose at higher temperatures into carbon and water.

Rotational isomers [edit]

Each glucose isomer is subject to rotational isomerism.

Within the cyclic form of glucose, rotation may occur around the O6-C6-C5-O5 torsion angle,

termed the ω-angle, to form three staggered rotamer conformations called gauche-gauche (gg),

gauche-trans (gt) and trans-gauche (tg).

For methyl α-D-glucopyranose at equilibrium the ratio of molecules in each rotamer conformation is

reported as 57:38:5 gg:gt:tg.^[13]

This tendency for the ω-angle to prefer to adopt a gauche conformation is attributed to the

gauche effect.

Physical properties [edit]

Solutions [edit]

Glucose 5%

All forms of glucose are colorless and easily soluble in water, acetic acid,

and several other solvents.

They are only sparingly 약간 soluble in methanol and ethanol.

The open-chain form is thermodynamically unstable,

and it spontaneously isomerizes to the cyclic forms.

(Although the ring closure reaction could in theory create four- or three-atom rings,

these would be highly strained and are not observed.)

In solutions at room temperature, the four cyclic isomers interconvert over a time scale of hours,

in a process called mutarotation.^[14]

Starting from any proportions, the mixture converges stable ratio of α:β= 36:64.

The ratio would be α:β = 11:89 if it were not for the influence of the anomeric effect.^[15]

Mutarotation is considerably slower at temperatures close to 0 °C.

Mutarotation consists of a temporary reversal of the ring-forming reaction,

resulting in the open-chain form, followed by a reforming of the ring.

The ring closure step may use a different -OH group than the one recreated by the opening step

(thus switching between pyranose and furanose forms),

and/or the new hemiacetal group created on C-1 may have the same or opposite handedness as

the original one (thus switching between the α and β forms).

Thus, though the open-chain form is barely detectable in solution,

it is an essential component of the equilibrium.

Solid state [edit]

Depending on conditions, three major solid forms of glucose can be crystallized from

water solutions: α-glucopyranose, β-glucopyranose, and β-glucopyranose hydrate.^[16]

Optical activity [edit]

Whether in water or in the solid form, D-glucose is dextrorotatory, meaning it will rotate the

direction of polarized light clockwise.

The effect is due to the chirality of the molecules, and indeed the mirror-image isomer,

L-glucose, is levorotatory (rotates polarized light counterclockwise) by the same amount.

The strength of the effect is different for each of the five tautomers.

Note that the D- prefix does not refer directly to the optical properties of the compound.

It indicates that the C-2 chiral center has the same handedness as that of D-glyceraldehyde

(which was so labeled because it is dextrorotatory).

The fact that D-glucose is dextrorotatory is a combined effect of its four chiral centers,

not just of C-2; and indeed some of the other D-aldohexoses are levorotatory.

Production [edit]

Metabolism of common monosaccharides and some biochemical reactions of glucose

Biosynthesis [edit]

In plants and some prokaryotes, glucose is a product of photosynthesis 광합성.

In animals and fungi, glucose results from the breakdown of glycogen,

a process known as glycogenolysis.

In plants the breakdown substrate is starch.

In animals, glucose is synthesized in the liver and kidneys from non-carbohydrate intermediates,

such as pyruvate, lactate and glycerol, by a process known as gluconeogenesis.

In some deep-sea bacteria, glucose is produced by chemosynthesis.

Commercial [edit]

Glucose is produced commercially via the enzymatic hydrolysis of starch.

Many crops can be used as the source of starch.

Maize, rice, wheat, cassava, corn husk and sago are all used in various parts of the world.

In the United States, cornstarch (from maize) is used almost exclusively.

Most commercial glucose occurs as a component of invert sugar,

a roughly 1:1 mixture of glucose and fructose.

In principle, cellulose could be hydrolyzed to glucose,

but this process is not yet commercially practical.^[16]

Sources and absorption [edit]

Most dietary carbohydrates contain glucose, either as their only building block,

as in starch and glycogen, or together with another monosaccharide, as in sucrose and lactose.

In the lumen of the duodenum and small intestine, the glucose oligo- and polysaccharides are

broken down to monosaccharides by the pancreatic and intestinal glycosidase

ther polysaccharides cannot be processed by the human intestine and require assistance by

intestinal flora if they are to be broken down;

the most notable exceptions are sucrose (fructose-glucose) and lactose (galactose-glucose).

Glucose is then transported across the apical membrane of the enterocytes by SLC5A1 (SGLT1),

and later across their basal membrane by SLC2A2 (GLUT2).^[17]

Some of the glucose is converted to lactic acid by astrocytes,

which is then utilized as an energy source by brain cells,

some of the glucose is used by intestinal cells and red blood cells,

while the rest reaches the liver, adipose tissue and muscle cells,

where it is absorbed and stored as glycogen (under the influence of insulin).

Liver cell glycogen can be converted to glucose and returned to the blood when

insulin is low or absent; muscle cell glycogen is not returned to the blood because of a lack of

enzymes.

In fat cells, glucose is used to power reactions that synthesize some fat types and have other

purposes.

Glycogen is the body's "glucose energy storage" mechanism,

because it is much more "space efficient" and less reactive than glucose itself.

In hypoglycemia저혈당 management [edit]

Individuals with diabetes or other conditions where hypoglycemia (low blood sugar) may occur

often carry small amounts of sugar in various forms.

One sugar commonly used is glucose, often in the form of glucose tablets

(glucose pressed into a tablet shape sometimes with one or more other ingredients as a binder).

History [edit]

Glucose was first isolated (from raisins) in 1747 by the German chemist Andreas Marggraf.^[18]

Because glucose is a basic necessity of many organisms, a correct understanding of its chemical

makeup and structure contributed greatly to a general advancement in organic chemistry.

This understanding occurred largely as a result of the investigations of Emil Fischer,

a German chemist who received the 1902 Nobel Prize in Chemistry as a result of his findings.^[19]

The synthesis of glucose established the structure of organic material and consequently formed

the first definitive validation of Jacobus Henricus van't Hoff's theories of chemical kinetics and

the arrangements of chemical bonds in carbon-bearing molecules.^[20]

Between 1891 and 1894, Fischer established the stereochemical configuration of all the known

sugars and correctly predicted the possible isomers, applying van't Hoff's theory of asymmetrical

carbon atoms.

Blood sugar

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The fluctuation of blood sugar (red) and the sugar-lowering hormone insulin (blue) in humans during the course of a day with three meals.

One of the effects of a sugar-rich vs a starch-rich meal is highlighted.^[1]

The blood sugar concentration or blood glucose level is the amount of glucose (sugar) present

in the blood of a human or animal.

The body naturally tightly regulates blood glucose levels as a part of metabolic homeostasis.

With some exceptions,^[2][3] glucose is the primary source of energy for the body's cells,^{[citation needed]}

and blood lipids (in the form of fats and oils) are primarily a compact energy store.

Glucose is transported from the intestines or liver to body cells via the bloodstream,

and is made available for cell absorption via the hormone insulin,

produced by the body primarily in the pancreas.

Glucose levels are usually lowest in the morning, before the first meal of the day

(termed "the fasting level"), and rise after meals for an hour or two by a few millimolar.

Blood sugar levels outside the normal range may be an indicator of a medical condition.

A persistently high level is referred to as hyperglycemia 고혈당;

low levels are referred to as hypoglycemia 저혈당.

Diabetes mellitus is characterized by persistent hyperglycemia from any of several causes,

and is the most prominent disease related to failure of blood sugar regulation.

Intake of alcohol causes an initial surge in blood sugar, and later tends to cause levels to fall.

Also, certain drugs can increase or decrease glucose levels.^[4]

Units [edit]

The international standard way of measuring blood glucose levels are in terms of a

molar concentration, measured in mmol/L (millimoles per litre; or millimolar, abbreviated mM).

In the United States, mass concentration is measured in mg/dL (milligrams per decilitre).^[5]

Since the molecular weight of glucose C₆H₁₂O₆ is 180, for the measurement of glucose,

the difference between the two scales is a factor of 18,

so that 1 mmol/L of glucose is equivalent to 18 mg/dL.^[6]

Normal values in humans [edit]

Normal value ranges may vary slightly among different laboratories.

Many factors affect a person's blood sugar level.

A body's homeostatic mechanism, when operating normally,

restores the blood sugar level to a narrow range of about 4.4 to 6.1 mmol/L (79.2 to 110 mg/dL)

(as measured by a fasting blood glucose test).^[7]

The normal blood glucose level (tested while fasting) for non-diabetics,

should be between 70 and 100 milligrams per deciliter (mg/dL).

The mean normal blood glucose level in humans is about 5.5 mM

(5.5 mmol/L or 100 mg/dL, i.e. milligrams/deciliter);^[6]

however, this level fluctuates throughout the day.

Blood sugar levels for those without diabetes and who are not fasting should be below

125 mg/dL.^[8]

The blood glucose target range for diabetics, according to the American Diabetes Association,

should be 90–130 (mg/dL) before meals, and less than 180 mg/dL after meals

(as measured by a blood glucose monitor).^[9]

Despite widely variable intervals between meals or the occasional consumption of meals with a

substantial carbohydrate load, human blood glucose levels tend to remain within the normal range.

However, shortly after eating, the blood glucose level may rise, in non-diabetics,

temporarily up to 7.8 mmol/L (140 mg/dL) or slightly more.

For people with diabetes maintaining 'tight diabetes control',

the American Diabetes Association recommends a post-meal glucose level of less than 10 mmol/L

(180 mg/dL) and a fasting plasma glucose of 3.9 to 7.2 mmol/L (70–130 mg/dL).^[10]

The actual amount of glucose in the blood and body fluids is very small.

In a healthy adult male of 75 kg with a blood volume of 5 liters,

a blood glucose level of 5.5 mmol/L (100 mg/dL) amounts to 5 grams,

slightly less than two typical American restaurant sugar packets for coffee or tea.^[11]

Part of the reason why this amount is so small is that,

to maintain an influx of glucose into cells,

enzymes modify glucose by adding phosphate or other groups to it.

Animals [edit]

In general, ranges of blood sugar in common domestic ruminants are lower than in many

monogastric mammals.^[12]

However this generalization does not extend to wild ruminants or camelids.

For serum glucose in mg/dL, reference ranges of 42 to 75 for cows, 44 to 81 for sheep,

and 48 to 76 for goats, but 61 to 124 for cats; 62 to 108 for dogs, 62 to 114 for horses,

A 90 percent reference interval for serum glucose of 26 to 181 mg/dL has been reported for

captured mountain goats (Oreamnos americanus),

where no effects of the pursuit and capture on measured levels were evident.^[14]

For beluga whales,

the 25–75 percent range for serum glucose has been estimated to be 94 to 115 mg/dL.^[15]

For the white rhinoceros, one study has indicated that the 95 percent range is 28 to 140 mg/dL.^[16]

For harp seals, a serum glucose range of 4.9 to 12.1 mmol/L [i.e. 88 to 218 mg/dL] has been

reported; for hooded seals, a range of 7.5 to 15.7 mmol/L [i.e. about 135 to 283 mg/dL] has been

reported.^[17]

Regulation [edit]

Main article: Blood sugar regulation

The body's homeostatic mechanism keeps blood glucose levels within a narrow range.

It is composed of several interacting systems, of which hormone regulation is the most important.

There are two types of mutually antagonistic metabolic hormones affecting blood glucose levels:

• catabolic hormones (such as glucagon, cortisol and catecholamines) which increase blood glucose;
• and one anabolic hormone (insulin), which decreases blood glucose.

Abnormality in blood sugar levels [edit]

High blood sugar [edit]

Main article: hyperglycemia 고혈당

If blood sugar levels remain too high the body suppresses appetite over the short term.

Long-term hyperglycemia causes many of the long-term health problems including heart disease,

eye, kidney, and nerve damage.

The most common cause of hyperglycemia is diabetes.

When diabetes is the cause,

physicians typically recommend an anti-diabetic medication as treatment.

From the perspective the majority of patients, treatment with an old,

well-understood diabetes drug such as metformin (내가먹는 약) will be the safest,

most effective, least expensive, most comfortable route to managing the condition.^[18]

Diet changes and exercise implementation may also be part of a treatment plan for diabetes.

Low blood sugar 저혈당[edit]

Main article: hypoglycemia

If blood sugar levels drop too low, a potentially fatal condition called hypoglycemia develops.

Symptoms may include lethargy 혼수, impaired mental functioning; irritability 과민성; shaking,

twitching 경련, weakness in arm and leg muscles; pale complexion 창백한안색;

sweating 식은땀;paranoid 편집증or aggressive mentality and loss of consciousness 의식손실.

Mechanisms that restore satisfactory blood glucose levels after extreme hypoglycemia

(below 40 mg/dl) must be quick and effective to prevent extremely serious consequences of

insufficient glucose: confusion or unsteadiness and,

in the extreme (below 15 mg/dl) loss of consciousness and seizures 졸도.

It is far more dangerous to have too little glucose in the blood than too much, at least temporarily.

In healthy individuals, blood glucose-regulating mechanisms are generally quite effective,

and symptomatic hypoglycemia is generally found only in diabetics using insulin or other

pharmacological treatment^{[dubious – discuss]}.

Hypoglycemic episodes can vary greatly between persons and from time to time,

both in severity and swiftness of onset.

For severe cases, prompt medical assistance is essential, as damage to brain and other tissues

and even death will result from sufficiently low blood-glucose levels.

Glucose measurement [edit]

Further information: Blood glucose monitoring and Glucose meter

Sample source [edit]

In a fasting individual, glucose levels are comparable in arterial, venous, and capillary blood.

But following meals, capillary and arterial blood glucose levels can be significantly higher than

venous levels.

This is because tissue cells consume some of the glucose in the blood as it passes

from arteries through the capillary bed and into the veins.^[19]

Although these differences vary widely,

one study found that following the consumption of 50 grams of glucose,

"the mean capillary blood glucose concentration is higher than the mean venous

blood glucose concentration by 35%."^[20]

Sample type [edit]

Glucose is measured in whole blood, plasma or serum.

Historically, blood glucose values were given in terms of whole blood,

but most laboratories now measure and report plasma or serum glucose levels.

Because red blood cells (erythrocytes) have a higher concentration of protein (e.g., hemoglobin)

than serum, serum has a higher water content and consequently more dissolved glucose than

does whole blood.

To convert from whole-blood glucose,

multiplication by 1.15 has been shown to generally give the serum/plasma level.

Collection of blood in clot tubes for serum chemistry analysis permits the metabolism of glucose

in the sample by blood cells until separated by centrifugation.

Red blood cells, for instance, do not require insulin to intake glucose from the blood.

Higher than normal amounts of white or red blood cell counts can lead to excessive glycolysis in

the sample, with substantial reduction of glucose level if the sample is not processed quickly.

Ambient temperature at which the blood sample is kept prior to centrifuging and separation of

plasma/serum also affects glucose levels.

At refrigerator temperatures, glucose remains relatively stable for several hours in a blood sample.

Loss of glucose can be prevented by using Fluoride tubes (i.e., gray-top)

since fluoride inhibits glycolysis.

However, these should only be used when blood will be transported from one hospital laboratory

to another for glucose measurement.

Red-top serum separator tubes also preserve glucose in samples after being centrifuged isolating

the serum from cells.

To prevent contamination of the sample with intravenous fluids, particular care should be given to

drawing blood samples from the arm opposite the one in which an intravenous line is inserted.

Alternatively, blood can be drawn from the same arm with an IV line after the IV has been turned

off for at least 5 minutes, and the arm has been elevated to drain infused fluids away from the vein.

Inattention can lead to large errors, since as little as 10% contamination with a 5% glucose solution

(D5W) will elevate glucose in a sample by 500 mg/dL or more.

Remember that the actual concentration of glucose in blood is very low, even in the hyperglycemic.

Measurement techniques [edit]

Two major methods have been used to measure glucose.

The first, still in use in some places, is a chemical method exploiting the nonspecific reducing

property of glucose in a reaction with an indicator substance that changes color when reduced.

Since other blood compounds also have reducing properties

(e.g., urea, which can be abnormally high in uremic patients),

this technique can produce erroneous readings in some situations

(5 to 15 mg/dL has been reported).

The more recent technique, using enzymes specific to glucose,

is less susceptible to this kind of error.

The two most common employed enzymes are glucose oxidase and hexokinase.

In either case,

the chemical system is commonly contained on a test strip which is inserted into a meter,

and then has a blood sample applied.

Test-strip shapes and their exact chemical composition vary between meter systems and

cannot be interchanged.

Formerly, some test strips were read (after timing and wiping away the blood sample) by visual

comparison against a color chart printed on the vial label.

Strips of this type are still used for urine glucose readings,

but for blood glucose levels they are obsolete.

Their error rates were, in any case, much higher.

More precise blood glucose measurements are performed in a medical laboratory,

using hexokinase, glucose oxidase, or glucose dehydrogenase enzymes.

Urine glucose readings, however taken, are much less useful.

In properly functioning kidneys,

glucose does not appear in urine until the renal threshold for glucose has been exceeded.

This is substantially above any normal glucose level,

and is evidence of an existing severe hyperglycemic condition.

However, as urine is stored in the bladder, any glucose in it might have been produced at any time

since the last time the bladder was emptied.

Since metabolic conditions change rapidly, as a result of any of several factors,

this is delayed news and gives no warning of a developing condition.

Blood glucose monitoring is far preferable, both clinically and for home monitoring by patients.

Healthy urine glucose levels were first standardized and published in 1965 ^[21] by Hans Renschler.

I. CHEMICAL METHODS
A. Oxidation-reduction reaction
1. Alkaline copper reduction
Folin-Wu method		Blue end-product
Benedict's method	Modification of Folin-Wu method for qualitative urine glucose
Nelson-Somogyi method		Blue end-product
Neocuproine method	*	Yellow-orange color neocuproine[22]
Shaeffer-Hartmann-Somogyi	Uses the principle of iodine reaction with cuprous byproduct. Excess I2 is then titrated with thiosulfate.
2. Alkaline Ferricyanide Reduction
Hagedorn-Jensen		Colorless end product; other reducing substances interfere with reaction
B. Condensation
Ortho-toluidine method	Uses aromatic amines and hot acetic acid Forms Glycosylamine and Schiff's base which is emerald green in color This is the most specific method, but the reagent used is toxic
Anthrone (phenols) method	Forms hydroxymethyl furfural in hot acetic acid
II. ENZYMATIC METHODS
A. Glucose oxidase
Saifer–Gerstenfeld method		Inhibited by reducing substances like BUA, bilirubin, glutathione, ascorbic acid
Trinder method	uses 4-aminophenazone oxidatively coupled with phenol Subject to less interference by increases serum levels of creatinine, uric acid or hemoglobin Inhibited by catalase
Kodak Ektachem	A dry chemistry method Uses reflectance spectrophotometry to measure the intensity of color through a lower transparent film
Glucometer	Home monitoring blood glucose assay method Uses a strip impregnated with a glucose oxidase reagent
B. Hexokinase
NADP as cofactor NADPH (reduced product) is measured in 340 nm More specific than glucose oxidase method due to G-6PO4, which inhibits interfering substances except when sample is hemolyzed

Blood glucose laboratory tests [edit]

1. fasting blood sugar (i.e., glucose) test (FBS)
2. two-hr postprandial blood sugar test (2-h PPBS)
3. oral glucose tolerance test (OGTT)
4. intravenous glucose tolerance test (IVGTT)
5. glycosylated hemoglobin (HbA_1C)
6. self-monitoring of glucose level via patient testing
7. Random blood sugar (RBS)
8. Average blood glucose may be estimated by measuring glycated hemoglobin (HbA1c)

Clinical correlation [edit]

The fasting blood glucose level, which is measured after a fast of 8 hours,

is the most commonly used indication of overall glucose homeostasis,

largely because disturbing events such as food intake are avoided.

Conditions affecting glucose levels are shown in the table below.

Abnormalities in these test results are due to problems in the multiple control mechanism of

glucose regulation.

The metabolic response to a carbohydrate challenge is conveniently assessed by a postprandial

glucose level drawn 2 hours after a meal or a glucose load.

In addition, the glucose tolerance test, consisting of several timed measurements after a

standardized amount of oral glucose intake, is used to aid in the diagnosis of diabetes.

Error rates for blood glucose measurements systems vary, depending on laboratories,

and on the methods used.

Colorimetry techniques can be biased by color changes in test strips

(from airborne or finger borne contamination, perhaps) or interference (e.g., tinting contaminants)

with light source or the light sensor.

Electrical techniques are less susceptible to these errors, though not to others.

In home use, the most important issue is not accuracy, but trend.

Thus if a meter / test strip system is consistently wrong by 10%, there will be little consequence,

as long as changes (e.g., due to exercise or medication adjustments) are properly tracked.

In the US, home use blood test meters must be approved by the Federal Food and Drug

Administration before they can be sold.

Finally, there are several influences on blood glucose level aside from food intake.

Infection, for instance, tends to change blood glucose levels,

as does stress either physical or psychological.

Exercise, especially if prolonged or long after the most recent meal, will have an effect as well.

In the normal person,

maintenance of blood glucose at near constant levels will nevertheless be quite effective.^{[clarification needed]}

Causes of abnormal glucose levels

Persistent hyperglycemia	Transient hyperglycemia	Persistent hypoglycemia	Transient hypoglycemia
Reference range, FBG: 70–110 mg/dL
Diabetes mellitus	Pheochromocytoma	Insulinoma	Acute alcohol ingestion
Adrenal cortical hyperactivity Cushing's syndrome	Severe liver disease	Adrenal cortical insufficiency Addison's disease	Drugs: salicylates, antituberculosis agents
Hyperthyroidism	Acute stress reaction	Hypopituitarism	Severe liver disease
Acromegaly	Shock	Galactosemia	Several glycogen storage diseases
Obesity	Convulsions	Ectopic insulin production from tumors	Hereditary fructose intolerance

Etymology and use of term [edit]

In a physiological context, the term is a misnomer because it refers to glucose,

yet other sugars besides glucose are always present.

Food contains several different types

(e.g., fructose (largely from fruits/table sugar/industrial sweeteners),

galactose (milk and dairy products),

as well as several food additives such as sorbitol, xylose, maltose, etc.).

But because these other sugars are largely inert with regard to the metabolic control system

(i.e., that controlled by insulin secretion), since glucose is the dominant controlling signal for

metabolic regulation, the term has gained currency, and is used by medical staff and lay folk alike.

The table above reflects some of the more technical and closely defined terms used in the medical field.

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