GLUCOSE METABOLISM..

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Originally, when glucose is used in context, it most importantly refers to nutrients gotten from carbohydrate consumption. It is one of the many forms of sugars found in the body, others which may include :- fructose , ribose, maltose, galactose and many others.

Glucose being a monosaccharide I.e contains one sugar. Is the most commonly found carbohydrate found in diet. It is also known as dextrose and blood sugar, and is commonly found in honey, fruits, vegetables and so on.

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Glucose is also a precursor for disaccharide formation ( lactose, maltose) and polysaccharide formation (cellulose). It has a structural formular shown in both straight chain configuration (fischer's projection) and ring structural configuration (Haworth projection) and is metabolised efficiently by the body and stored as glycogen in mammals and starch in plants.

OVERVIEW.

In normal individuals, glucose plasma levels is normally maintained within a range of 4-7 mM which indicates a balance either due to release of glucose by absorption by the intestine or breakdown of glycogen and uptake and metabolism by the tissues in the body.

Metabolism efficiently discusses both the breakdown of glucose, the build up or formation of glucose from other sources, the absorption by the body, digestion of orally consumed sources of glucose, the role of hormones in these processes as well.

The metabolic processesof glucose are:-
Glycolysis
Gluconeogeneis
Glycogenolysis
Glycogenesis.

Glycolysis.

Glucose, a six carbon sugar is broken down by a ten steppes enzymatic pathway to produce pyruvate, a three carbon sugar. This pyruvate produved may either enter into the tricarboxylic acid pathway or may be converted into triacylglycerides. Glycolysis takes place in the cytosol of organisms and does not require the use of oxygen.
The ten steps of the pathway each is carried out by a specific enzyme with either the use or production of ATP. ( energy being one of the end products in the form of ATP).

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GLUCONEOGENESIS.

Glucose regulation in the body is solely as a result of this pathway which helps to prevent hypoglycemia ( low bood glucose).

In a fed state, the body's glucose supply is maintained by constant breakdown into pyruvate. But in a fasting state, glucose supply is cut short and this process sets in. Glucose is released from the breakdown of lactate, citric acid cycle intermediates and transamination and deamination of amino acids like leucine, glycerol and isoleucine by the donation of their carbon skeleton serving as feeder pathways for glycolysis. This pathway mostly occurs in the liver and is associated with low carbohydrate levels and ketosis.

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GLYCOGENOLYSIS.

Glycogen breakdown to glucose.
The body's primary store of energy s glycogen in muscle and liver tissues. This glycogen is a multi-functional polysaccharide found in the form of granules in the cell cytoplasm. It provides glucose in conditions of low glucose level and acts in response to hormonal and neural signals.

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GLYCOGENESIS.

Glycogen is formed by the incorporation of one glucose molecule (in the form of glucose 6 phosphate) into the branched polymeric structure.

HORMONAL REGULATION.

Basically, secondary messengers produce by the bodies endocrine glands that function in the metabolic processes of the body. Hormones are specific signalling molecules that act as chemical messengers. They are transported in the circulatory system after production to their target organs.
Hormones involved in glucose refulation are:-

ADIPOCYTE HORMONES.

LEPTIN.

Produced by brown adipose tissues, skeletal muscle, stomach, ovaries .e.tc. Leptin plays an improtant role in glucose metabolism by controlling appetite.
When fat mass falls in a fasting stae, plasma leptin levels falls leading to an increase in appetite and suppressed energy expenditure. The reverse occurs in a fed state when fat mass rise.

RESISTIN

These are cysyeine rich protein molecules which induce insulin like body resistance thereby linking diabetes to obesity.

ADIPONECTIN.

This has been associated with lipid metabolism in insulin sensitive tissues.

GUT HORMONES.

INCRETIN.

This gut hormome as the name implies is secreted by the gut.
It is released after food ingestion and it stimulates the release of insulin more potent than the release noted in intravenous release of glucose. Incretin types that have ben associated with glucose metabolism include:-

• GIP
• GLP-1.
  The chart below shows the action of Incretin.

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PANCREATIC HORMONES.

The pancreatic cells (alpha and beta) secrete Insulin and Glucagon respectively.

When blood glucose level increases, the action of the secreted insulin reduces it by :-

• stimulating storage of glycogen in the muscle and adipose tissues.
• reducing glucose production and release by the liver through inhibition of glycogen breakdown.
• increasing glucose uptake in the muscle and fat by triggering translocation of the Glut4 transporter to the plasma membrane.

GLUCAGON.

Glucagon opposes the effect of insulin by stimulating hepatic glucose production to sustain the body in a fasting state.
It stimulates the liver to breakdown glycogen to rlease glucose.

ACTION OF GLUCAGON.

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References:- 1, 2