The mouth is part of the digestive system. There are teeth, tongue, and salivary glands in the mouth. The cavity of the mouth is divided into two portions: the vestibule and the cavity proper. The vestibule of the mouth is a space bounded by the lips and cheeks. The lips and cheeks contain the mimic muscles. The oral cavity is bounded by the hard and soft palates. The hard palate separates the oral cavity from the nasal cavity. The mucous membrane covers the lips, and cheeks to the alveolar processes of the jaws. In the mouth the food is ground by the teeth and mixed with water, mucus and other secretions of the salivary glands. Saliva has a direct influence on the teeth and provides the optimal level of metabolic activity in the body. It consists of 99.5 % water and 0.5 % total solids. Saliva dissolves some of the solid substances when they are brought in contact with taste buds which stimulate appetite. Moistening food with saliva enables to facilitate swallowing.

There are many salivary glands in the mouth. Three principal pairs are recognized: sublingual, submaxillary, and parotids. The salivary glands regulate the water supply of the body.

Exercise 3.21. Answer the following questions:

1) What portions is the cavity of the mouth divided into?

2) What covers the lips, cheeks and the alveolar processes of the jaws?

3) What is the food ground by? What is the food mixed with in the mouth?

4) What influence does saliva have?

5) How do the secretions of salivary glands facilitate the process of food swallowing?

Exercise 3.22. Learn the active vocabulary to Text 2:

human embryo – эмбрион человека

stomodeum – стомодеум, первичный рот

to establish – устанавливать

ectoderm – эктодерм

mesenchyme – мезенхима

connective tissue – соединительная ткань

odontogenesis –одонтогенез

tissue formation – формирование ткани

ectomesenchyme – нейромезенхима

neural crest cells – клетки нервного гребня

to extend – простираться, расширяться

concurrently – при этом, параллельно

primary dental lamina – первичная зубная пластинка

maxillary arch – верхнечелюстная дуга

knob – выпуклость, бугорок

to enlarge – увеличиваться, расширяться

to acquire – приобретать

cap – защитное покрытие пульпы

utero – внутриутробное (нахождение)

dental papilla – зубной сосочек

fibrous – волокнистый

to encircle – окружать

dental sac – зубной мешочек

deposition – смещение

to attain – досягать, добираться

fetus – зародыш

homogenous texture – гомогенная структура

postnatal – постнатальный

infant – младенец, новорожденный

ingestion – поглощение, прием внутрь

Exercise 3.23. Read Text 2 and make a summary considering the stages of teeth development:

Text 2. Tooth Development

Before a human embryo is 3 weeks old, the stomodeum is established. The primitive mouth is lined with ectoderm, beneath which is mesenchyme. The ectoderm gives rise to the oral epithelium, and the mesenchyme becomes the underlying connective tissue.

Odontogenesis is the name given to the origin and tissue formation of the teeth. Not all teeth start development at the same time. A tooth is formed from ectoderm and ectomesenchyme. Ectomesenchyme is derived from neural crest cells. Development begins with the formation of the primary dental lamina, extending along the jaws on a line where the teeth will later appear.

Concurrently with the development of primary dental lamina, at 10 places in the mandibular and at 10 places in the maxillary arch some cells of the dental lamina multiply and 10 little knobs of epithelial cells are forming on the dental lamina in each jaw. Each of these knob-shaped structures is an early enamel organ. It is the beginning of the tooth germ of a primary tooth. A tooth germ is derived from two embryonic tissues: the part that develops from the dental lamina originates from ectoderm and the remaining parts originate from mesenchyme underlining ectoderm.

As the dental lamina enlarges, the enamel organ acquires the shape of a cap. By the 8^th week in utero this cap formation is seen in the enamel organs of the deciduous incisor tooth germs. The connective tissue inside the cap undergoes a number of changes and becomes the dental papilla. The connective tissue beneath the dental papilla becomes fibrous and encircles the papilla forming the dental sac.

The crown and the root of the tooth grow as the result of the deposition of new layers of enamel and dentin on previously formed layers. When the final size of the enamel crown has been attained, the enamel-forming cells disappear and further formation of enamel is impossible.

The fetus derives its mineral from mother through placenta. That’s why the dentin formed in utero is always of a more homogenous texture and more mineralized than that laid down postnatally. In the young child, the pulp cavity is quite large relative to amount of dentin already formed. For this reason, capping of teeth may be delayed for several years until the formation of the dentin has been completed. So the infant is fully dependent on the mineral obtained through ingestion.