. Digestive System The process of digestion involves intake of the food (Ingestion), breakdown of the food into micromolecules (Digestion), absorption of these molecules into the blood stream (Absorption), the absorbed substances becoming components of cells (Assimilation) and elimination of the undigested substances (Egestion). Digestive system includes the alimentary canal and associated digestive glands. .
. Structure of the Alimentary Canal The alimentary canal is a continuous, muscular digestive tract that begins with an anterior opening, the mouth and opens out posteriorly through the anus. The alimentary canal consists of mouth, buccal cavity, pharynx, oesophagus, stomach, intestine, rectum and anus (Figure. .
). The mouth is concerned with the reception of food and leads to the buccal cavity or oral cavity (Figure. . ).
Mechanical digestion is initiated in the buccal cavity by chewing with the help of teeth and tongue. Chemical digestion is through salivary enzymes secreted by the salivary glands. Each tooth is embedded in a socket in the jaw bone this type of attachment is called thecodont . Human beings and many mammals form two sets of teeth during their life time, a set of temporary milk teeth (deciduous teeth) which gets replaced by a set of permanent teeth (adult teeth).
This type of dentition is called diphyodont . The permanent teeth XI Std Biology-Zoology Chapter- swallowing. Two masses of lymphoid tissue called tonsils are also located at the sides of the pharynx. Oesophagus is a thin long muscular tube concerned with conduction of the food to a ‘J’ shaped stomach passing through the neck, thorax and diaphragm.
A cardiac sphincter (gastro oesphageal sphincter) regulates the opening of oesophagus into the stomach (Figure. . ). If the cardiac sphincter does not contract properly during the churning action of the stomach the gastric juice with acid may flow back into the oesophagus and cause heart burn, resulting in GERD (Gastero Oesophagus Reflex Disorder).
The stomach functions as the temporary storage organ for food and is located in the upper left portion of the abdominal cavity. It consists of three parts – a cardiac portion into