Mouth
Mouth Food enters the digestive system via the mouth or oral cavity,
mucous membrane lined. The lips (labia) protect its outer opening, cheeks
form lateral walls, hard palate and soft palate form anterior/posterior
roof. Communication with nasal cavity behind soft palate. Floor is muscular
tongue. Tongue has bony attachments (styloid process, hyoid bone) attached
to floor of mouth by frenulum.
Posterior exit from mouth guarded by a ring of palatine/lingual tonsils.
Enlargement = sore throat, tonsillitis.
Food is first processed (bitten off) by teeth, especially the anterior
incisors. Suitably sized portions then retained in closed mouth and chewed
or masticated (especially by cheek teeth, premolars, molars) aided by
saliva Ducted salivary glands open at various points into mouth. This
process involves teeth (muscles of mastication move jaws) and tongue (extrinsic
and intrinsic muscles). Mechanical breakdown, plus some chemical (ptyalin,
enzyme in saliva). Taste buds allow appreciation, also sample potential
hazards (chemicals, toxins)
Swallowing
In leaving the mouth a bolus of food must cross the respiratory tract
(trachea is anterior to oesophagus) by a complicated mechanism known as
swallowing or deglutination which empties the mouth and ensures that food
does not enter the windpipe.
Swallowing involves co-ordinated activity of tongue, soft palate pharynx
and oesophagus. The first (buccal) phase is voluntary, food being forced
into the pharynx by the tongue. After this the process is reflex. The
tongue blocks the mouth, soft palate closes off the nose and the larynx
rises so that the epiglottis closes off the trachea. Food thus moves into
the pharynx and onwards by peristalsis aided by gravity. If we try to
talk whilst swallowing food may enter the respiratory passages and a cough
reflex expels the bolus.