Digestion : It is a hydrolytic process and is carried out by a number of enzymes. The process of digestion converts larger and complex food materials into smaller food particles which become easier to absorb. In fact it is a process of nutrition.
Digestive system : The digestive system contains alimentary canal and the associated glands. The digestion starts from mouth and gets completed in the large intestine.
Various organs of digestive system are:
(a) The Buccal Cavity : Mouth or buccal cavity contains teeth and tongue. Teeth help in cutting the coarse food material while tongue adds saliva secreted by salivary glands. Four pairs of salivary glands secrete saliva which contains ptylin. The four glands are : (a) sublingual glands, (b) Infra-orbital glands, (c) Paratid glands, (d) sub maxillary glands. The process of digestion starts from mouth.
(b) The Pharynx : It is a wide tube. It is also called pharyngeal cavity. The posterior wall of pharynx has two openings—oesophagus and larynx.
(c) Oesophagus : It is a muscular tube about 10 inches long extending from the pharynx to the stomach.
(d) Stomach : It is a bag like structure and Jshaped. It has four regions namely the cariac, the fundus, the body and the pyloric.
(e) Small intestine : Small intestine is a coiled tube about 7m long. It is divided into three parts namely duodenum, Jejunum and ileum.
(f) Large intestine : The large intestine is wider than small intestine. It is about 1.5m long. It is divided into two parts—colon and rectum.
Digestion
1. In Mouth : Teeth break down the food in to small pieces. It is masticated and mixed with saliva. Salivery amylase changes starch into maltose. Maltase enzyme converts maltose into glucose.
2. In Stomach : In stomach digestive gastric Juice (Water, mucin, salt, hydrocliloric acid) and three enzymes (pepsin, rennin and lipase) get mixed with the food. The food digestion proceeds further.
3. Small intestine : In small intestine three types of juices get mixed. These are :
(a) Pancreatic Juice (trypsin, chymotrypsin, carboaypeptidase, amydase, lipase, maltase, ribonuclease) (b) Intestinal juice (erepsin maltase, sucrase, lactase, peptidase, lipase) and (c) Bile juice.
4. Large intestine : Here no digestion takes place but to a small extent the cellulose gets digested in colon in herbivores.
ABSORPTION
Stomach in man is resposible for minor absorption of water and mineral salts. Major absorption takes place in small intestine.
Defecation
Defecation is egestion of undigested part of the food. Stercobillin and ruobillin are responsible for its colour.
FOOD
Major constituents of food : The major constituents of food are carbohydrates, proteins, fats, vitamins, water, minerals and roughage.
Carbohydrates : Carbohydrates are organic compounds containing carbon hydrogen and oxygen. All carbohydrates have H2 and O2 as 1:2 ratio.
They are synthesized by green plants by the process of photosynthesis.
Cereals, millets, pulses, roots (sweet potato and beet), tubers (potato), fruits, sugar, jaggery, honey, milk and milk products are the main sources of dietary carbohydrates.
Carbohydrates are the main sources of energy.
Proteins : Proteins are organic compounds containing carbon, hydrogen, oxygen and nitrogen.
Some proteins contain sulphur and phosphorus also.
Legumes, pulses, nuts, oilseeds, meat, eggs, milk and milk products except butter and ghee are the main sources of dietary proteins. Almond is the richest source of proteins. It contains about 18% proteins. Ground nut is also very rich in proteins.
Proteins are essential for the growth and maintenance of the body.
Fats : Fats are organic compounds which contain carbon, hydrogen and oxygen.
Oil seed, vanaspati ghee, milk and milk products like cream, khoya, ghee, butter, egg yolk, fish and fish liver oil are the main sources of dietary fats.
Fats are a rich source of energy. They are insoluble in water but soluble in organic solvents.
Vitamins : Vitamins are vital organic substances occurring in different natural foods. Vitamins are health maintaining foods. We get vitamins from fruits and vegetables and also from milk and eggs.
Water : Drinking water and water present in food substances are the main source of water for the body. Our body contains about 65% of water.
Roughage : The coarse undigestible matter of food is called roughage.
It mostly contains cellulose fibres present in plant foods.
The roughage induces peristalsis and regulates bowel movements.
Balanced Diet : The diet which provides all the nutrients in adequate amounts and in proper proportion according to an individual’s age, sex and physical activity is called a balanced diet. In a balanced diet all the six components should be in the proper proportions.
Reasons for taking a Balanced Diet:
(1) A balanced diet provides sufficent amount of nutrients for the growth and development of the body.
(2) A balanced diet prevents diseases and gives good health.
(3) Balanced diet compensate the wear and tear of the body.
(4) A balanced diet gives storage of nutrients for an emergency.
(5) A balanced diet gives the necessary amount of calories to the body.
Imbalanced Diet : The diet which does not contain all the essential nutrients in proper proportion and shows deficiency or increase in one or more major food constituents is called imbalanced diet.
Malnutrition : The disordered nutrition is called malnutrition. Malnutrition is a condition in which a person suffers due to lack or deficiency of one or more essential nutrients of food in the diet.
Diseases caused by Malnutrition : Malnutrition causes many deficiency diseases, some of which are as follows :
(1) Kwashiorker : It is caused by the deficiency of proteins in the diet.
(2) Marasmus : It is caused due to the deficiency of carbohydrates, proteins and fats in the diet.
(3) Goitre : It is caused due to the deficiency of iron in the diet.
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