The accessory organs of digestion are: 1. The teeth 2. Three pairs of salivary glands 3. The pancreas 4. The liver and the bilary duct.
The alimentary tract is made up of four layers of tissues
1. Outer covering or Adventitia
2. Muscular layer
3. Sub mucous layer
4. The inner most layer is the mucous membrane. The Mouth, Pharynx, Salivary glands, Esophagus
The mouth is the upper expanded part of the alimentary canal, bounded externally by the lips and cheeks. The part of the mouth outside the gums and teeth is called the vestibule, and the remainder of the cavity, the mouth proper, which contains the tongue. The roof of the mouth is formed by the hard and soft palates and the anterior two-thirds of the tongue fill the floor of the mouth. The soft palate has a cone-shaped prolongation at its posterior which hangs down in the back of the mouth and is called the Uvula. On either side of the Uvula are two folds of mucous membrance, the anterior and posterior pillars of the faces, between which lie the tonsils.
The tongue is a muscular organ, which occupies the floor of the mouth and is attached to the hyoid bone and the mandible. It is covered with a modified mucous membrance, which is rough due to the presence of little projections called as the papillae. These contain the nerve endings of the sense of taste also called as the taste buds. The tongue plays an important part in the mastication (chewing), deglutition (swallowing) and speech. It is also the organ of taste.
Each individual has two sets of teeth, the temporary and the permanent teeth- which appear at different periods of life. The first set is the deciduous or temporary teeth which appear when the child is 6 months old and should all be present by the end of 24 months. They are 20 in number, 10 in the upper jaw, and 10 in the lower jaw.
The second set or the permanent teeth begins to replace the first set in the 6th year of age and is usually complete by the 25th year. They are 32 in number, 16 in the upper jaw and 16 in the lower jaw.
According to the shape and position, teeth have been classified as:
1. The incisor teeth – cutting teeth
2. The Canine teeth – grasping teeth
3. Premolar teeth
4. Molar teeth – Grinding teeth
The teeth are essential for efficient mastication, which helps in proper digestion of food.
The Salivary glands
There are three pairs of salivary glands- the parotid, sub mandibular (sub maxillary), and sublingual. The parotid gland is the largest and lie just below the ear. The sub mandibular and the sublingual gland both open into the floor of the mouth. They secret saliva which enters the mouth by means of their duct.
1. Parotid gland
2. Sub mandibular gland
3. Sublingual gland
These are two in number and situated one on each side of the face just below the external acoustic meatus (ear cannel). Each gland has a parotid opening into the mouth at the level of the second upper molar teeth.
Sub mandibular Glands:
These are two in number and smaller than the parotid glands. Each is situated on each side of the face under the angle of the jaw. The sub mandibular or Wharton’s duct passes forward in the floor of the mouth one on each side of the frenulum of the tongue.
These glands lay under the mucous membrane of the floor of the mouth in front of the sub mandibular glands. They have numerous small ducts which pierce the mucous membrane of the floor of the mouth.
The saliva is a mixed secretion of the three pairs of salivary glands which enter the floor of the mouth by means of ducts. It consists of:
Water – 90%
Enzyme – Ptyalin, which acts on cooked starch in the mouth converting to maltose.
Mucin – Secreted by the glands in the mouth
Reaction – Alkaline
The pharynx is an expanded portion of the alimentary canal about 5 inches long and is divided into three parts.
1. The Nasopharynx
2. The Oropharynx
3. The Laryngopharynx
Of these, only the oropharynx and laryngopharynx are associated with the alimentary tract. Food passes from the oral cavity to the pharynx then to the oesophagus below, with which it is continuous.
The oesophagus or gullet is a muscular tube about 25 cm (10 inches) extending from the pharynx above to the cardiac orifice of the stomach below. It at the level of the sixth cervical vertebra and descends through the mediation in of the vertebral column and behind the trachea. The oesophagus has four coats and) similar in structure to the remainder of the alimentary canal. Food passes through oesophagus by the movement of the muscles fibers running through it, by an action can as peristalsis. Peristalsis is a wave of muscular contraction, preceded by a wave relaxation, which causes the food to move onwards. It takes about 9 seconds to pass bolus of food from the pharynx to the stomach.