The digestive system begins with the oral cavity. The oral cavity is bounded by the hard and soft palate, the inner surface of the cheeks and lips, and the jaw-hyoid muscle.
The mucous membrane of the oral cavity has many small salivary glands, and three pairs of large glands (parotid, sublingual and submandibular) are remote from the oral cavity and communicate with it by ducts. All glands secrete saliva.
The teeth are located in the oral cavity. An adult normally has 32 teeth: 8 incisors, 4 canines, 8 small molars and 12 large molars. Children first have 20 milk teeth, which are gradually replaced by permanent ones. Teeth grind and grind food and participate in the formation of speech.
A tooth consists of a root, a neck and a crown. Outside, the crown is covered with durable enamel. Underneath is dentin, a special type of bone tissue. The inside of a tooth is filled with pulp, a loose connective tissue that contains blood vessels and nerves. The neck and crown of the tooth are covered with cement (a type of bone).
The tongue is a muscular organ covered with a mucous membrane. In the mucous membrane, taste buds are located, with the help of which we perceive the taste of food. The tongue moves food, forms a lump, and facilitates swallowing. Language plays an important role in the formation of articulate speech.
From the oral cavity, a lump of food enters the pharynx – a muscular organ connected to the esophagus and larynx. When swallowing, the entrance to the respiratory organs is blocked by the epiglottis, and the food lump is pushed into the digestive tract.
The esophagus is a muscular tube about 25 cm long, through which food moves into the stomach. This happens due to peristalsis (wave-like contraction of muscle walls).