Mouth and accessory organs
The mouth is the opening of the GI tract, or otherwise known as the alimentary canal. The internal lining of the mouth, cheeks and lips is mucous membrane. It is composed of a nonkeratinized stratified squamous epithelium as it requires a thick protective layer for abrasion and bacteria. Unlike keratinized epithelium (e.g. skin) which is water resistant, nonkeratinized supports the maintenance of moisture within the mouth. (Martini F.H. et al, 2006). The function of the mouth organ is to ingest food, a voluntary process of putting food into the oral cavity. The interior consists of the buccal mucosa ‘bucca = cheeks’ (Tortora, G. et al, 1996), which are the inner facings of the cheek and the soft and hard palate which form both the front and back roof of the mouth. The uvula muscle (accessory organ) obstructs food and liquid from entering the nasal cavity allowing them to follow down the GI tract (Tortora, G. et al, 1996). There are 3 primary salivary glands (accessory organs) which lie outside the oral cavity. The parotid glands sit at the rear end of the mandibular bone, beneath the ears. Entering the mouth behind the second upper molar via the parotid duct, secretes a thin substance of saliva due to the parotid gland being made up entirely from serous acini cells. The salvia contains a huge quantity of amylase, a digestive enzyme which begins to break down food molecules (Martini F.H. et al, 2006). This process is called chemical digestion, a key process in the digestive system. The submandibular gland is situated at the rear end beneath the floor of the mouth and the sublingual gland slightly to the front. The submandibular secretes into the lingual frenulum via the Wharton’s duct. It secretes a slightly thicker substance as the gland compromises of mucous acini aswell as its bigger counterpart serous acini. Amylase secretes from serous acini. Glycoproteins and buffers are secreted from the mucous acini. Buffers maintain a pH balance at an approximate of 7.0 which neutralises the acids in the mouth and glycoproteins contribute to lubrication. The sublingual gland is predominantly made up of mucous acini and only a few serous acini cells, secreting its formation of salvia beneath the tongue via several ducts. The three glands make up the salvia producing 1.-1.5 liters a day. 99.4% constitutes water and the 0.6% glycoproteins, buffers, enzymes and other needed substances (Martini F.H. et al, 2006). Lysozymes are also found in the mouth preventing the mouth from a bacteria build up, i.e. one benefit is its defense against tooth decay. Salvia not only plays an important role in chemical digestion but assists in speech, wets the food in preparation and protects the oral cavity from bacteria (Martini F.H. et al, 2006).