ANATOMY OF THE DIGESTIVE SYSTEM PART I Oral region Stomach Pharynx Small intestine Esophagus Large intestine 18.11.2014 Kaan Yücel M.D., Ph.D. http://fhs121.org A TOTAL OF 21 FIGURES INSERTED IN THE TEXT READABILITY SCORE 44 % Dr.Kaan Yücel http://fhs121.org Digestive system – Part I 1. ORAL REGION includes the oral cavity (mouth), teeth, gingivae (gums), tongue, palate, and the region of the palatine tonsils. The digestion starts here in the oral cavity. It is the place where the food is ingested and prepared for digestion in the stomach and small intestine. Food is chewed by the teeth, and saliva from the salivary glands facilitates the formation of a manageable food bolus (L. lump). Swallowing is voluntarily initiated in the oral cavity (Oral phase). The voluntary phase of the process pushes the bolus from the oral cavity into the pharynx, where the involuntary (automatic) phase of swallowing occurs. The three phases of swallowing: Oral phase, pharyngeal phase, and esophageal phase. Throat Virtual Tour ORAL CAVITY The oral cavity (mouth) is inferior to the nasal cavities and extends from the lips to the pharynx. The roof of the oral cavity consists of the hard and soft palates. The floor is formed mainly of soft tissues, which include a muscular diaphragm and the tongue. The lateral walls (cheeks) are muscular and merge anteriorly with the lips surrounding the oral fissure (the anterior opening of the oral cavity). The oral cavity is continuous with the cavity of the pharynx at the oropharyngeal isthmus. The oral cavity is separated into two regions by the upper and lower dental arches consisting of the teeth and alveolar bone that supports them. The outer oral vestibule is a slit-like space. It is between the dental arches and the deep surfaces of the cheeks and lips. The oral fissure opens into it. The oral fissure can be opened and closed by muscles of facial expression, and by movements of the lower jaw.The duct of the parotid salivary gland (Stensen’s duct) opens on a small papilla into the vestibule opposite the upper second molar tooth. The inner oral cavity proper (mouth proper) is the space between the upper and lower dental arches (maxillary and mandibular alveolar arches and the teeth they bear). It is enclosed by the dental arches. The oral cavity has multiple functions: • It is the inlet for the digestive system involved with the initial processing of food, which is aided by secretions from salivary glands. It is in the oral cavity that food and drinks are tasted and where mastication and lingual manipulation of food occur. • It manipulates sounds produced by the larynx and one outcome of this is speech. • It can be used for breathing because it opens into the pharynx, which is a common pathway for food and air. For this reason, the oral cavity can be used by physicians to access the lower airway. Lips & Cheeks The lips are mobile, musculofibrous folds surrounding the mouth and are covered externally by skin and internally by mucous membrane. The lips function as the valves of the oral fissure, containing the sphincter (orbicularis oris) that controls entry and exit from the mouth and upper alimentary and respiratory tracts. The cheeks (L. buccae) form the movable walls of the oral cavity. Teeth The teeth are set in the tooth sockets. There are 20 deciduous teeth and 32 permanent teeth: four incisors, two canines, four premolars, and six molars in each jaw. They begin to erupt at 6 years of age. The last tooth to erupt is the third molar, which may happen between the ages of 17 and 30. The chief functions of the teeth are to: • Incise, reduce, and mix food material with saliva during mastication (chewing). • Help sustain themselves in the tooth sockets by assisting the development and protection of the tissues that support them. • Participate in articulation (distinct connected speech). Gingivae (Gums) The gingivae (gums) are composed of fibrous tissue covered with mucous membrane. The gingiva proper (attached gingiva) is firmly attached to the alveolar processes of the mandible and maxilla and the necks of the teeth. 1 Dr.Kaan Yücel http://fhs121.org Digestive system – Part I Tongue The tongue is a mass of striated muscle covered with mucous membrane. The tongue forms part of the floor of the oral cavity and part of the anterior wall of the oropharynx. Its anterior part is in the oral cavity and is somewhat triangular in shape with a blunt apex of tongue. The apex is directed anteriorly and sits immediately behind the incisor teeth. The root of tongue is attached to the mandible and the hyoid bone. The muscles attach the tongue to the styloid process and the soft palate above and to the mandible and the hyoid bone below. The superior surface of the oral or anterior two-thirds of the tongue is oriented in the horizontal plane. The pharyngeal surface or posterior one-third of the tongue curves inferiorly and becomes oriented more in the vertical plane. Papillae The superior surface of the oral part of the tongue is covered by hundreds of papillae. There are four types of papillae in the tongue: filiform papillae are small cone-shaped projections of the mucosa that end in one or more points; fungiform papillae are rounder in shape and larger than the filiform papillae, and tend to be concentrated along the margins of the tongue; the largest of the papillae are the vallate papillae, which are blunt-ended cylindrical papillae invaginations in the tongue's surface-there are only about 8 to 12 vallate papillae in a single V-shaped line immediately anterior to the terminal sulcus of tongue; foliate papillae are linear folds of mucosa on the sides of the tongue near the terminal sulcus of tongue. The papillae in general increase the area of contact between the surface of the tongue and the contents of the oral cavity. All except the filiform papillae have taste buds on their surfaces. The undersurface of the oral part of the tongue lacks papillae, but does have a number of linear mucosal folds. A single median fold (frenulum of tongue) is continuous with the mucosa covering the floor of the oral cavity. On each side of the frenulum is a lingual vein, and lateral to each vein is a rough fimbriated fold. The oral and pharyngeal surfaces are separated by a V-shaped terminal sulcus of tongue. This terminal sulcus forms the inferior margin of the oropharyngeal isthmus between the oral and pharyngeal cavities. At the apex of the V-shaped sulcus is a small depression (foramen cecum of tongue), which marks the site in the embryo where the epithelium invaginated to form the thyroid gland. In some people a thyroglossal duct persists and connects the foramen cecum on the tongue with the thyroid gland in the neck. The mucosa covering the pharyngeal surface of the tongue (posterior one-third of the tongue) is irregular in contour because of the many small nodules of lymphoid tissue in the submucosa. These nodules are collectively the lingual tonsil. There are no papillae on the pharyngeal surface. Muscles The tongue is completely divided into a left and right half by a median sagittal septum composed of connective tissue. This means that all muscles of the tongue are paired. The muscles of the tongue are divided into two types: intrinsic and extrinsic. Intrinsic muscles are confined to the tongue and are not attached to bone and alter the shape of the tongue. The extrinsic muscles are attached to bones and the soft palate. Intrinsic muscles The intrinsic muscles of the tongue originate and insert within the substance of the tongue. They are divided into superior longitudinal, inferior longitudinal, transverse, and vertical muscles, and they alter the shape of the tongue. Working in pairs or one side at a time the intrinsic muscles of the tongue contribute to precision movements of the tongue required for speech, eating, and swallowing. Extrinsic muscles Extrinsic muscles of the tongue originate from structures outside the tongue and insert into the tongue. These muscles protrude, retract, depress, and elevate the tongue. There are four major extrinsic muscles on each side. 1. Genioglossus: make a substantial contribution to the structure of the tongue. They occur on either side of the midline septum that separates left and right halves of the tongue. These muscles stick the tongue out. 2 Dr.Kaan Yücel http://fhs121.org Digestive system – Part I 2. Hyoglossus: thin quadrangular muscles lateral to the genioglossus muscles which depress the tongue. 3. Styloglossus: originate from the anterior surface of the styloid processes of the temporal bones. They enter the lateral surface of the tongue where they blend with the superior margin of the hyoglossus and with the intrinsic muscles. The styloglossus muscles retract the tongue and pull the back of the tongue superiorly. 4. Palatoglossus: [1] muscles of the soft palate and the tongue. Each originates from the undersurface of the palatine aponeurosis and passes anteroinferiorly to the lateral side of the tongue. The movements of the palatoglossus muscle facilitate closing of the oropharyngeal isthmus and as a result separate the oral cavity from the oropharynx. Unlike other muscles of the tongue, but similar to most other muscles of the soft palate, the palatoglossus muscles are innervated by the vagus nerves [X]. The rest of the intrinsic muscles of the tongue are innervated by the hypoglossal nerve [XII]. Asking a patient to "stick your tongue out" can be used as a test for the hypoglossal nerves [XII]. If the nerves are functioning normally, the tongue should protrude evenly in the midline.