The mouth
  1. Mechanical and chemical digestions both begin in the mouth.
  2. Chewing is the first step in mechanical digestion.
  3. During chewing, salivary glands produce saliva, which mixes with the chewed food. Enzymes in the saliva kill bacteria and begin the process of chemical digestion by breaking down starches to sugars.
  4. Human teeth are well adapted for chewing many kinds of food. The 32 teeth of the normal adult have three basic shapes, each with a different function:
  1. Incisors - sharp front teeth used for biting into and tearing pieces of food.
  2. Canines - pointed teeth (vampire) next to incisors, used to tear or shred food.
  3. Molars - teeth at the back of the mouth, have large flat surfaces that crush and grind food.
  1. Every tooth has two main parts: the crown and the root.
  2. A tooth is made of four layers of tissue: enamel, dentin, cementum, and periodontal membrane (ligament).
  3. The crown is covered by enamel, a calcium-containing material that is the hardest substance in the body.
  4. Dentine a bone like tissue makes up most if the inside of a tooth.
  5. Cementum in a tiny layer covers the dentine of the root.
  6. The periodontal ligament holds the tooth in its socket.
  7. Once the teeth and salivary glands have completed the initial processing, the food is ready to be swallowed.
  8. Gathering the food together in a ball called a bolus; the tongue pushes it toward the back of the mouth and the pharynx.
  9. The pharynx is an area at the back of the throat that connects the nose and mouth to the GI track and respiratory tracts.
  10. In the pharynx, the GI track and the respiratory system cross each other.
  11. As the tongue moves food into the pharynx, it presses down on a small flap of cartilage called the epiglottis. When the epiglottis is depressed, it closes the entrance to the respiratory track and guides the food down the GI track.

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