Digestion in the mouth. Mastication.

The digestive system consists of the alimentary canal and related or accessory organs. The alimentary canal is formed by the mouth, pharynx, esophagus, stomach, small intestine, large intestine and rectum. The accessory structures are the teeth, tongue, salivary glands, hard and soft palates, liver, gallbladder and pancreas. The oral and laryngeal portions of the pharynx serve as a channel for the passage of both food and air. Food is conducted through it from the mouth to the esophagus.

The sight, smell, and thought of food may elicit salivary and gastric secretion. These juices cannot be effective, however, before food enters the body. After the entrance into the mouth the food undergoes a twofold reduction: a mechanical one and a chemical one. The process of mechanical reduction of food is called mastication.

This reduction is accomplished by the masticatory apparatus formed by:

- a hard framework – the skeleton and the temporomandibular joint;

- the muscles of mastication;

- a system of organs for grasping food and preparing it for swallowing (the lips, the

cheeks, muscles of facial expression, soft palate and tongue);

- special organs for mechanical grinding of the food – the teeth;

- organs that discharge mucus, secretions and enzymes – the glands;

- a specific nerve apparatus that ascertains the special qualitative features of the food

(the taste apparatus) and

- a large receptor area responsible for the perception of tactile, thermal and all other

types of external stimuli.

So mastication may be considered the first step in digestion. In man the act of mastication has more significance than the mere grinding of food before swallowing. While food is being chewed it is moved about in the mouth so that the taste buds are stimulated and odors are released to stimulate the olfactory epithelium. On these stimuli depends much of the satisfaction and pleasure of eating, which in turn initiate the process of gastric secretion.

The end product of mastication is the bolus, a mass of food moistened with saliva. In this form the food passes into the stomach.

Grammar

Find the examples of Gerund in the text, state the functions of the verbs.

2. Insert the prepositions where it is necessary:

1. The digestive system consists … the alimentary canal and related or accessory organs. 2. The alimentary canal is formed … the mouth, pharynx, esophagus, stomach, small intestine, large intestine and rectum. 3. The oral and laryngeal portions of the pharynx serve … a channel … the passage … both food and air. 4. The reduction of food is accomplished … the masticatory apparatus. 5. A large receptor area is responsible … the perception of external stimuli. 6. The vitamin deficiency results … hemorrhage, and edema of the gingival connective tissue. 7. This growth is correlated … and dependent … the erup­tion of teeth. 8. Considerable hemorrhage followed … the tooth extraction.

Translate the sentences, define non-finite verb forms.

1. This syndrome is quite serious; if unrecognized and untrea­ted, it may result in death. 2. The contact point is the point on the proximal surface of a tooth which touches a neighbouring tooth. 3. Pre-pain sensation, elicited by three kinds of electrical sti­mulation in human maxillary anterior teeth of adult men, was investigated. 4. In March the patient returned to the office complai­ning of a vague pain in the maxillary left posterior region. 5. The patient, a 24-year old male, appeared in January complaining of pain in the maxillary left posterior region and the sensation of something growing there. 6. In a report the author stated that caries was inhibi­ted by the same water, containing flouride that produced mottled enamel. 7. Denture laboratories are described, three of them being one-man laboratories. 8. The number of teeth extracted for various reasons was from 1 to 6, the average being 4 in both groups of patients. 9. Several large scale investigations have been conducted, with encouraging results reported. 10. The tooth was embedded in the lingual soft tissues, with root pointing backward. 11. Treatment consists of removing and correcting local irri­tating factor and providing the child with a nutritionally balan­ced diet and dental prophylaxis.

Summary