UNIT 7 The Digestive System

The digestive system consists of the alimentary canal and the accesson,. organs: tongue, teeth, salivary glands, pancreas and liver.The alimentary canal (digestive tube) is a continuous tube about thirty feet (9 ml long, which extends from the mouth to the anus. The greater part is coiled up in the cavity of the abdomen.The mouth is a oeaily oval-shaped cavity ; behind it communicates with the pharynx. The roof is formed by the hard and ,soft palate, and the greater part of the floor is formed by the tongue. The space hounded externally by the lips and cheeks and internally by the gums and teeth is called the vestibule. The cavity behind this is the mouth cavity proper.The pharynx, or throat cavity, is a musculo-membranous tube shaped like a cone, with its broad end turned upward and its constricted end downward to end in the esophagus. The pharynx communicates with the nose, ears, mouth and larynx by seven apertures.At the lower end of the pharynx, behind the trachea, begins the esophagus, a muscular tube, about nine to ten inches long. It 'descends %in front of the vertebral column. passes through the diaphragm, and terminates in the upper or cardiac end of the stomach.After the esophagus perforates the diaphragm it ends in the stomach, which serves as a temporary receptacle for food. The shape and position of the stomach are modified by changes within itself, and in the surrounding organstThese modifications are determined by (1) the amount of the stomach; contents, (2) the stage of digestion which has been reached, (3) the degree of development and power of the muscular walls. and (4) the 'condition of the adjacent intestines. It is never entirely empty but always contains a few cubic centimeters of gastric fluid or mein. When contracted, the shape of the s'..,,mach is comparable to a sickle or sausage. The stomach presents two openings and two borders or curvatures. The opening by which the stomach communicates with the esophagus is known as the cardia or esophageal orifice, and the Orifice which communicates with the duodenum is knpwn as the pylorus. Both apertures are guarded by ring-like muscles known as sphincters which, when contracted, keep the orifices closed.The small intestine extends from the pylorus to the colic valve. It is a convoluted tube about twenty-three feet in length. For descriptive purpose, the small intestine is divided into three portions : the duodenum, jejunum, and iletim.The large intestine is only about five feet long, but is wider than the small intestine. It extends from the ileum to the anus. It is divided into four parts: the cecum with the vermiform appendix, colon, rectum and anal canal.The accessory organs of digestion are : the tongue, the teeth, the salivary dands, the pancreas and the liver.The tongue is the special organ of the sense of taste. It assists in mastiand digestion.cation, deglutition