Mastication

Mastication of chewing is the process by which food is crushed and ground by teeth. It is the first step of digestion, and it increases the surface area of foods to allow more efficient beak down by enzymes. During the mastication process, the food is positioned by the cheek and tongue between the teeth for grinding. The muscles of mastication move the jaws to bring the teeth into intermittent contact, repeatedly occluding and opening. As chewing continues, the food is made softer and warmer, and the enzymes in saliva begin to break down carbohydrates in the food. After chewing, the food (now called bolus) is swallowed. It enters the esophagus and via peristalsis continues on to the stomach, where the next step of digesting occurs.

Saliva

Saliva is secreted by salivary glands, 99.5% water, plus electrolyte, mucus, white blood cells, epithelial cells, glycoproteins, enzymes, antimicrobial agents such as IgA and lysozyme.

Functions

Saliva contributes to the digestion of food and to the maintenance of oral hygiene. Without normal salivary function the frequency of dental caries, gum disease, and other oral problems increase significantly.

Role in taste

Saliva is very important in the sense of taste. It is the liquid medium in which chemicals are carried to taste receptor cells (mostly associated with lingual papillae).

Persons with little saliva often complain of dysgeusia （味覚異常）(i.e. disordered taste, e.g. reduced ability to taste, or having a bad, metallic taste at all times).

Dysphagia

Dysphagia is the medical term for the symptom of difficulty in swallowing. Although classified under “symptom and signs” in ICD-10, the term is sometimes used as a condition in its own right. Sufferers are sometimes unaware of their dysphagia.

It is usually caused by nerve or muscle problems. Dysphagia may occur after a stroke, throat and mouth cancer, gastroesophageal reflux disease, or as symptom of several different neurological disorders. It may be a sensation that suggests difficulty in the passage of solids or liquids from the mouth to the stomach, a lack of pharyngeal sensation, or various other inadequacies of the swallowing mechanism. Dysphagia is distinguished from other symptoms including odynophagia, which is defined as painful swallowing, and globus, which is the sensation of a lump in the throat. A psychogenic dysphagia is known as phagophobia.

PEG Percutaneous endoscopic gastrostomy

Percutaneous endoscopic gastrostomy (PEG) is an endoscopic medical procedure in which a tube (PEG tube) is passed into a patient‘s stomach through the abdominal wall, most commonly to provide a means of feeding when oral intake is not adequate (for example, because of dysphagia or sedation). This provides enteral nutrition (making use of the natural digestion process of the gastrointestinal tract) despite bypassing the mouth; enteral nutrition is generally preferable to parenteral （消化管以外を通しての投薬等）nutrition (which　is　only　used　when　the　GI　tract　must　be　avoided).　The　PEG procedure is　an　alternative　to open surgical gastrostomy insertion, and does not require a general anesthetic; mild sedation is typically used. PEG tubes may also be extended into the small intestine by passing jejunal extension tube (PEG-J tube) through the PEG tube and into the jejunum via the pylorus.