Carbohydrates have prominent physiological importance in the body.
Without them there exists no physiology in the body and also life on the earth.
After water and protein they comprise largest matter in the body and are major nutrients of the body.
The carbohydrate chemistry is basically comprised of 3 elements viz. carbon, hydrogen and oxygen.
So the name Carbo-hydrate (as carbon and hydrate i.e H2O respectively).
The food we eat mostly comprises of carbohydrates to a greater extent than other macro and micro-nutrients.
Function of carbohydrates include:
1 Provide instant energy to the body: This appears to be the 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.This glucose after being absorbed into blood reaches all the body tissues and cell.
There it gets metabolized to release energy in the from of ATP in the 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.
2 Reserve food for the body emergency: The excess glucose in the body is converted to glycogen due to the stimulation by the hormone insulin. 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.
3 Carbohyrdrates form 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.
4 Detoxification of the body by metabolism: Many drugs, toxic wastes in the body are metabolized for easy excretion in the body.
Some of these are water insoluble and hence they are 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 the body. Thus detoxification of physiological importance is carried out to some extent with carbohydrate derivatives.
5 As reaction intermediates or accessories: Carbohydrates participate as reaction intermediates in some vital reactions.
This function of carbohydrates is seen extensively in various cellular reaction. For example, 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.
6 Constitute genetic material: Carbohydrates form a part of genetic material like DNA and RNA in the form of deoxyribose and ribose sugars. This as carbohydrates form heptulose sugars which are used to form ribose sugars (pseudo-heptulose pathway)
7 They are constituents of all the cellular organelles like cell membrane, mitochondria, nucleus, endoplasmic reticulum etc. in one or other way to give structural integrity. They help make up the body mass by being included in all the parts of the cell and tissues. For example, in cell membranes, there are two constituents i.e. glycolipid layer and glycoprotein layer. Here the term “glyco” is a carbohydrate……
8They form components of bio-molecules which have a key role in blood clotting, immunity, fertilization etc.Thus they take part in many physiological reaction.
9 Transport of oxygen: Glucose is taken by red blood cells. These are the types of blood cells which lack mitochondria and other cell organelles required for production energy. In such case the ATP is produced by non-oxidative pathway (lactose 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.
10 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.
Carbohydrates in the body exist as 3 forms like
Monomers of Carbohydrates act as building block of higher carbohydrates. They form different compounds as mentioned below.
1. Mono & Disaccharides : These are simple carbohydrates involved in energy production cycles and other functions as mentioned above.
2. Oligosaccharides (few set of monosaccharides ) which have some special function by being included in most cell membranes or plasma membranes. For example by being part of plasma membranes of Red blood cells (i.e. erythrocytes) they help in damage of erythrocytes by liver by indication of their time for damage.
3. Polysaccharides These are complex carbohydrates. They are formed by long chain of monosaccharides and help in food reserve as glycogen in animals and starch in plants.
Thus function of carbohydrates is diverse and of vital physiological importance in the body. Though they are very vital, their imbalance can be trouble some in some disorder like diabetes etc.