The four primary functions of carbohydrates in the body are to provide energy, store energy, build macro molecules, and spare protein and fat for other uses. Some important function of carbohydrates includes:
Provide instant energy to the body
It appears as primary function of carbohydrates in the body. Carbohydrates which we consume as food in the form of starch (ex: potato, bread), sucrose (ex: sugar, fruits) etc. get digested in the body to release glucose.
Glucose after being absorbed into blood reaches all the body tissues and cell where it gets metabolized to release energy in the form of ATP in presence of oxygen inside the mitochondria. Thus energy is produced in the body due to breakdown of carbohydrates and it is the prime function of carbohydrates.
Reserve food for the body emergency
Excess glucose in body is converted to glycogen due to stimulation by insulin hormone. Glucose in blood is converted into glycogen and stored in the liver for future needs like starvation. Some of the glycogen is also reserved in muscles. In times of starvation, this glycogen converts back to glucose and provides energy.
Formation of other bio-molecules
Carbohydrates in excess are converted into other bio-molecules of physiological importance like fats, by fatty acid synthesis reaction in the cell for storage in the body and use in times of starvation. They form components of bio-molecules which have a key role in blood clotting, immunity, fertilization etc.
Detoxification of the body by metabolism
Many drugs, toxic wastes in body are metabolized for easy excretion. Some of these are water insoluble and hence difficult to be expelled in urine. Body converts them into glucouronyl conjugates using the glucouronyl moiety derived from carbohydrates.
A carbohydrate moiety like glucose combines with uronic acid to form glucouronate. These conjugates of insoluble substances with glucouronyls are more water-soluble and easily excreted from body. Thus detoxification of physiological importance is carried out to some extent with carbohydrate derivatives.
Reaction intermediates or accessories
Carbohydrates participate as reaction intermediates in some vital reactions. This function of carbohydrates is seen extensively in various cellular reaction. E.g. Vitamin B2 i.e. Riboflavin has ribose sugar (4 carbon) a type of carbohydrate in its chemical structure and involved in vital reactions at cellular level. As such carbohydrates are constituents of many hormones, vitamins, enzymes etc.
Constituents of genetic material
Carbohydrates form a part of genetic material like DNA and RNA in the form of deoxyribose and ribose sugars. Heptulose and pentose sugars are used to form ribose sugars.
Constituents of cellular organelles
Carbohydrates in one or other way to give structural integrity like cell membrane, mitochondria, nucleus, endoplasmic reticulum etc. They help make up body mass by being included in all parts of cell and tissues. E.g., in cell membranes, there are two constituents i.e. glycolipid layer and glycoprotein layer.
Transport of oxygen
Glucose is taken by red blood cells. These are blood cells which lack mitochondria and other cell organelles required for production of energy. In such case the ATP is produced by non-oxidative pathway. This energy thus produced is necessary for hemoglobin to bind to oxygen molecules and aid in transfer of oxygen from lungs to the different tissues.
Aid in gut motility
Carbohydrates form fibrous material. When carbohydrates are digested, this material absorbs water in the guts, swells and increases the load. This load is useful to increase intestinal motility and expulsion of waste (feces). Thus carbohydrates help clear gut and prevent constipation.
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