Advanced Nutrition and Dietetics in Gastroenterology, First Edition. Edited by Miranda Lomer. © 2014 John Wiley & Sons, Ltd. Published 2014 by John Wiley & Sons, Ltd. Chapter 1.1 1.1.1 Physiology The mouth is an important organ as it is the entry point into the gastrointestinal (GI) tract and damage and disease can compromise dietary intake. Even very minor disorders can have a profound impact on nutritional status. Anatomy The oral cavity consists of a number of structures. The lips surround the mouth and comprise skin externally and a mucous membrane (which has many minor salivary glands) internally, which together with saliva ensure adequate lubrication for the purposes of speech and mastication. The cheeks make up the sides of the mouth and are similar in structure to the lips with which they are continuous but differ in containing a fat pad in the subcutaneous tissue. On the inner surface of each cheek, opposite the upper second molar tooth, is an elevation that denotes the opening of the parotid duct which leads back to the parotid gland located in front of the ear. The palate (roof of the mouth) is concave and formed by the hard and soft palate. The hard palate is formed by the horizontal portions of the two palatine bones and the palatine portions of the maxillae (upper jaws). The hard palate is covered by thick mucous membrane that is continuous with that of the gingivae. The soft palate is continuous with the hard palate anteri- orly and with the mucous membrane covering the floor of the nasal cavity posteriorly. The soft palate is made up of a fibrous sheet together with the glossopalatine and pharyngopalatine muscles and the uvula hangs freely from its posterior border. The floor of the mouth can only be seen when the tongue is raised and is formed by the mucosa overlying the mylohyoid muscle. In the midline is the lingual frenum (a fold of mucous membrane), on either side of which is the opening of the submandibular duct from the associated subman- dibular gland. The gingivae form a collar around the neck of the teeth and consist of mucous membranes connected by thick fibrous tissue to the periosteum surround- ing the bones of the jaw. The gingivae are highly vascular and well innervated. The teeth are important in mastication and in humans, who are omnivores, they enable both plant and animal tissue to be chewed effectively. Each tooth consists of a crown, which varies in shape dependent on the position in the mouth, and one or more roots. There are eight permanent teeth in each quadrant, consisting of two incisors, a canine, two premolars and three molars, resulting in a total of 32 permanent teeth. The tongue is a highly mobile, muscular organ in the floor of the mouth which is important in speech, chewing and swallowing. In conjunction with the cheeks, it guides food between the upper and lower teeth until mastication is complete. The taste buds situated on the tongue are responsible for the sensation of taste (salt, bitter, sweet and sour). Physiology and function of the mouth Michael P. Escudier King’s College London and Guy’s and St Thomas’ NHS Foundation Trust London, UK COPYRIGHTED MATERIAL