Human Digestive system

Human digestive system

The process of nutrition in man is holozoic. In this type of nutrition, the nutrients are made available to the body through digestion of food. In digestion, the macromolecules or biopolymers of food are hydrolysed to yield their corresponding monomers. This process is facilitated by enzymes. Thus the digestive system comprises the alimentary canal, associated glands and regions of absorption of food. The digestive tract comprises various organs from mouth to anus. Mouth or Buccal cavity The opening of the oral cavity is bounded by the lips. The lips are muscular folds covered internally by mucosa. The lateral walls of the oral cavity are the cheeks. The inner walls of the cheeks are lined by moist stratified squamous epithelium. The lips and cheeks are useful in the process of mastication and speech.

Tongue : 
   It is a large muscular organ. It is attached to the floor of the oral cavity. The anerior part of the tongue is free. A thin fold of tissue called the frenulum attaches the free end to the floor of the mouth. The tongue is divided into two parts by a groove called the terminal sulcus. About two thirds of the anterior surface is covered by papillae. Some of them contain taste buds.

Teeth :
   There are 32 teeth in the mouth of a human adult. These are called as permanent teeth. There are 4 different types of permanent teeth seen. This nature is known as heterodontism. The types of teeth are incisors(8), canines(4), premolars(8) and molars(12). Since the teeth in the right and left side of the mouth are mirror images of each other, the dental arrangement is represented as follows.

i 2/2 : c 1/1 : pm 2/2 m 3/3 X 2

Each tooth consists of three regions. These are the upper crown, middle neck and basal root regions. The crown region has one or more cusps. The tooth is made up of a calcified tissue called dentine. The dentine of the tooth crown is covered by an extremely hard substance called enamel. The surface of the dentine in the root is covered with a bonelike substance called cementum. It helps to anchor the tooth in the jaw. In the centre of the tooth there is a pulp cavity. This cavity is also called as the root canal. This canal contains blood vessels and nerves. The canal opens at the base through apical foramen.

The teeth are set in sockets along the edges of the upper and lower jaws. This region of the jaw is covered by dense fibrous connective tissue and stratified squamous epithelium. It is called as the gingiva.

dentine

1 pulp cavity with nerve and
2 blood vessels
3 root canal
4 apical foramen
5 crown
6 neck
7 root
8 enamel
9 cementum

Salivary glands :
   These are scattered throughout the oral cavity. Three pairs of glands are larger. They are the parotid, submandibular and sublingual glands. The Parotid glands are the largest.They are located just anterior to the ear on each side of the head. The submandibular glands are found on the inferior borders of the mandible. The sublingual glands are the smallest. They lie immediatly below the mucous membrane in the floor of the mouth. There are other numerous small, coiled, tubular glands in the mouth. They are the lingual (tongue), palatine(palate), buccal and labial(lips) glands.