3.0. INTRODUCTION

Vertebrates require energy for the performance of several activities or functions such as respiration, excretion, reproduction, movement, thinking etc. Such energy is obtained by breaking down of food substances into smaller absorbable forms. the product of digestion will now be broken down to provide energy for metabolic processes.

3.1. DEFINITION OF DIGESTION

Digestion is the biological process by which food substances such as carbohydrates, proteins, lipids etc are broken down into smaller absorbable forms. Digestive processes take place specialized tissues, organs called the alimentary canal. This process takes in two stages. These are

3.1. Chemical stage

3.2. Mechanical stage

3.1. Mechanical stage.

The mechanical stage of digestion is the phase during which food substances are mechanically destroyed by the teeth within the mouth. This stage helps in the destruction of the cell walls, fibres contained in the food substances. This stage is imitated and confined within the mouth or buccal cavity.

3.2. Chemical stage.

The chemical stage is the stage whereby the mechanical destroyed substances are subjected to chemical substances such as the enzymes, bile etc. Enzymes help in further breaking down of the food substances into smaller absorbable forms. Chemical digestion of food substances starts from the mouth and ends in the small intestine.

3.2. THE DIGESTIVE TRACT/ALIMENTARY CANAL

The alimentary is a system of tissues, organs through which digestive processes take place. This system starts from the mouth and ends in the anus. It is about 9 metres long. The digestive tract or alimentary canal comprised of the following parts:

3.2.1. Mouth
3.2.2. Pharynx
3.3.3. Oesophagus
3.3.4. Stomach
3.3.5. Small intestine
3.3.6. Large intestine