NO.4 1. Introduction of Alimentary System 2. Oral Cavity

Chapter 2 The Alimentary System

Introduction Every cell in the body requires a constant source of energy in order to perform its particular functions—these functions are contraction, secretion, synthesis, or any other. Ingested food provides the basic materials from which this energy is produced and new molecules are synthesized. Most food, however, cannot enter the bloodstream and be used by the cells of the body until it is broken down into simpler molecules. The digestive system alters the ingested food by mechanical and chemical processes so that it can ultimately cross the wall of the gastrointestinal tract and enter the blood vascular and lymphatic systems. The vascular system then carries these food molecules through the hepatic portal vein to the liver before distributing them to cells throughout the body. After entering the cells, the digested food molecules may be reassembled into proteins, carbohydrates, and lipids, or they may be used in the production of energy to support body activity.

Constitution: 1. Alimentary canal and certain accessory organs. 2. Alimentary glands. The alimentary system (or digestive system) comprises the alimentary canal (gastrointestinal tract) and certain accessory organs including lips and cheeks, palate, tongue, and teeth, as well as glands (salivary glands, liver and pancreas).

Functions: Ingestion of food into the mouth Movement of food along the digestive tract Mechanical preparation of food for digestion Chemical digestion of food Absorption of digested food into the circulatory and lymphatic systems Elimination of indigestible substances and waste products from the body by defecation

Alimentary canal The alimentary canal about 9 m long extends from the mouth to the anus. It consists of the following 6 parts: The mouth The pharynx The esophagus The stomach Small intestine: is divided into three parts: the duodenum, jejunum, and ileum. Large intestine

Section 1 The Oral Cavity The oral cavity (mouth) is the first part of the digestive tract. It extends from the lips to the oropharynx.

Division: Oral vestibule and Oral cavity proper: Oral vestibule: an outer, smaller part. It is a slit-like space, bounded externally by the oral lips and cheeks, internally by the gums and teeth. It communicates with the exterior by the oral fissure. When the teeth are occluded it communicates with the oral cavity proper by an aperture behind the 3rd molar teeth on each side, and by narrow clefts between contiguous teeth.

On the inner surface of the cheek, opposite the crown of 2nd upper molar tooth, a small papilla marks the opening of the parotid duct. Oral cavity proper: an inner, large part. It is bounded laterally and in front by the alveolar arches, the teeth and gums; behind, it communicates with the pharynx by isthmus of fauces (the oropharyngeal isthmus) between the palatoglossal arches. The roof of the oral cavity consists of the hard palate and soft palate, while the greater part of the floor is formed by the tongue.

Ⅰ. The Oral Lips Construction: Each lip consists mainly of muscle covered by skin externally and mucous membrane internally. The red margin of the lips is seen where the skin meets the mucous membrane.

Ⅱ. The Cheeks They have a structure similar to the lips –an outer skin, an inner mucous membrane and a layer of muscle in between. The parotid duct opens on the inside of the cheeks opposite the upper second molar tooth.

Ⅲ. The Palate It constitutes the roof of the mouth and the floor of the nasal cavity. Composition: two regions; The hard palate: an anterior two-thirds. The hard palate is formed by palatine processes of the maxillae and the horizontal plates of the palatine bones. It is covered with a dense tissue, formed by the periosteum and mucous membrane.

The soft palate: a posterior one-thirds The soft palate: a posterior one-thirds. The soft palate hangs like a curtain between the mouth and the oropharynx. Uvula, Palatoglossal arch, Palatopharyngeal arch, Isthmus of fauces: The palatoglossal arch runs downward to the side of the base of the tongue and forms the lateral boundary of the isthmus fauces. Tonsillar fossa.

Ⅳ. The Palatine Tonsils The palatine tonsils, which are composed mainly of lymphoid tissue, are located in the tonsillar fossae.

Ⅴ. The Teeth (Dentes) Two sets of teeth in man: Deciduous (milk) and permanent. Basic shape: all teeth have a similar basic structure Crown: projecting above the gum Root (or roots): in the jaw and a narrowed part Neck: between the crown and the root

Structure: Dentine: the bulk of the tooth consists of dentine. Enamel: over the dentine of the crown is the enamel. Cement: round the dentine of the root is the cement. Periodontal membrane: attaches the root of the tooth to its socket.

Cavum dentis (dental cavity) and dental pulp: there is a small opening called the apical foramen at the apex of the root through which vessels and nerves pass to and form the dental pulp. The cavum dentis, (or dental cavity) within a tooth, is divided into the cavity of the crown and a root canal, both filled with dental pulp.

Dental arrangement: Deciduous teeth: 20 in number. 5 in each quadrant. They are, from the midline in front passing laterally and backwards, 2 incisors, 1 canine and 2 molars. Permanent teeth: 32 in number, 8 in each quadrant. They are, from the midline in front and going backwards, 2 incisors, 1 canine, 2 premolars, and 3 molars. The third molars are also called wisdom teeth. Sometimes the third molars do not erupt.

Dental functions: In general the incisors and canine are for cutting and the premolars and molars for masticating. The periodontal structure: the sockets and the gums (gingivae) together with the periodontal membrane are usually called the periodontal structure.

Ⅵ. The Tongue (Lingua) The tongue forms the floor of the mouth. It is composed of interwoven bundles of skeletal muscles covered with mucous membrane. The shape of tongue: The tongue has a root, an apex, a dorsum and an inferior surface. The dorsum: has a V-shaped groove called the terminal sulcus. It serves as the boundary between the oral part (or anterior 2/3) , and pharyngeal part (or posterior 1/3) of the tongue.

Papillae: The mucous membrane that covers the dorsum of the tongue is modified by the presence of numerous small projections called papillae. There are three types of papillae on the tongue.

Vallate papillae: They are about 1～2mm in diameter and form a row in each side just in front of and parallel to the terminal sulcus. Each papilla is a flat-topped elevation of mucous membrane and surrounded by a deep groove. In the walls of the groove are studded with taste buds.

Fungiform papillae: They are found chiefly on the sides and tip of the tongue and appeared as red spots. These papillae also have taste buds. Filiform papillae: They are conical in shape and are found over the dorsum of the front part of the tongue. These papillae have no taste buds.

The mucous membrane of the inferior surface of the tongue: Frenulum of tongue is a vertical fold of mucous membrane in the midline between the tongue and the floor of the mouth. Sublingual caruncle Sublingual fold

Lingual muscles: Including two types of muscles The extrinsic muscles of the tongue connect the tongue to the base of the skull above and behind, to the hyoid bone below, to the jaw below and in front and to the soft palate above. The extrinsic muscles of the tongue are three on each side: hyoglossus, styloglossus, genioglossus.

The intrinsic muscles are originate and insert in the tongue The intrinsic muscles are originate and insert in the tongue. Their fibers run in various directions and modify the shape of the tongue in many different ways. Action of tongue: the tongue can be raised, depressed, protruded and retraceted by these muscles.

Ⅶ. The Salivary Glands About 1000 to 2000 ml of saliva is secreted daily into the mouth. There are three pairs of the major salivary glands whose ducts open into the mouth. There are also much minor salivary glands in the lips, cheeks, tongue and palate. The major salivary glands comprise three large paired masses- the parotid, submandibular and sublingual glands.

Ⅰ). The Parotid Gland The largest pair. Shape: an inverted, flattened, three sided pyramid. Location: It lies below the external acoustic meatus, between the mandible and the sternocleidomastoid. Parotid duct: each parotid gland has a duct (parotid duct) that passes forwards across the masseter muscle and then turns inwards. It pierces the buccinator and opens upon a small papilla on the oral surface of the cheek opposite the crown of the second upper molar tooth.

Ⅱ). The Submandibular Gland Shape: it is irregular in form and about the size of a chestnut. Location: it lies in the upper part of the neck under the skin below the floor of the mouth and deep to the body of the mandible. Submandibular duct: is about 5 cm long, opens on the sublingual caruncle at the side of the frenulum of the tongue.

Ⅲ). The Sublingual Gland Shape: narrow, flattened, shaped somewhat like an almond. Location: it is located on the floor of the mouth within a fold of mucous membrane. Sublingual duct: each sublingual gland has several small ducts that open onto the floor of the mouth on the summit of the sublingual fold; and, occasionally a few open into the duct of the submandibular gland.