Digestion





What is Digestion?

Commonly we think that it is very easy to define digestion. All of us have some feeling about the subject of digestion. The amount of food that an organism ingests is determined principally by the intrinsic desire for food. The normal diet, which meet various requirements of the body includes such components as carbohydrates, lipids, proteins, vitamins, minerals and water. Out of these, water, minerals, vitamins, free monosaccharides and amino acids can be assimilated as such.




But most foodstuffs are ingested in forms that are unavailable to the organism, since they can not be absorbed from the digestive tract until they have been broken down into smaller molecules. As for instance, carbohydrates must be hydrolysed into monosaccharides, fats into glycerol and fatty acids, and proteins into amino acids. Disintegration of naturally occurring foodstuffs into assimilable forms is the process of digestion. Digestion involves splitting of food molecules by hydrolysis into smaller molecules that can be absorbed through the epithelium of the gastro-intestinal tract.

What are the Types of Digestion?

Mainly the digestion is of two types. Those are:
i) Intracellular Digestion
ii) Extracellular Digestion

Intracellular Digestion

Intracellular Digestion is found in protozoans and in some multicellular animals like Hydra, echinoderms, etc. is found in protozoans and in some multi-cellular animals like Hydra, Echinoderms, etc. When the procedure of digestion takes place inside the cell, it is known as intracellular digestion. The cell engulfs food materials by endocytosis, which is then digested by the enzymes inside the cell. The digested products pass to the cytoplasm across the endocytotic vesicle membrane.




Extracellular Digestion

Extracellular Digestion occurs in most multi-cellular animals. The process of digestion which takes place outside the cells in narrow cavities which is called digestive tract is known as extracellular digestion. In this type of digestion the food is ingested and carried to a complex digestive tract. The digestive tract has separate openings for food ingestion and for removal of undigested remnants. This one-way system permits food to be ingested and held while faeces are collected and expelled at the same time. Each segment of the tract is dedicated to perform a particular function. The food passes through a sort of assembly line from the mouth to anus. The degree of specialization is the greatest in the vertebrate digestive tract, which consists of specific regions for different functions; those are the initial preparation of food, storage, digestion, absorption, and formation and removal of faeces. Each region is separated from the other by special circular muscles called sphincters. These muscles can contract to close off that region of the tract. Such an arrangement enhances the efficiency of digestion and absorption.




What is digestive System?

The digestive system which is concern with digestion consists of the digestive tract or alimentary canal which forms a continuous passage from the mouth to the anus. The food is taken by the mouth, and sent downwards. As the food moves downwards into the alimentary canal, it comes in contact with a series of juices, called digestive juices, which contain various enzymes. In the digestive tract, the food is broken down. As a result of that the carbohydrates, fats, proteins, minerals, vitamins, etc. that it contains may be absorbed into the blood stream to fuel the body. The unabsorbed food bits and pieces are passed out from the alimentary canal by a process called egesting. The digestive system differs widely in different animals though it has basic similarities in structure and functions of digestion.

Now let us have a details about Human digestive system. Just click here →