Structure and Function of the Digestive System
The major function of the digestive system is to break down large macromolecules, that cannot be absorbed, into smaller molecules that can be absorbed through the walls of the tube and into the circulatory system. The digestive system, is like a tube that runs from the mouth to the anus. You can divide the digestive system into two parts, the Aliementary tract, and accessory organs. The aliementary tract consists of the mouth, pharnyx, esophagus, small and large intestines, rectum, and anus. The accessory organs are the salivary glands, liver, gallbladder, and pancreas.
- The mouth, or oral cavity, is the first organ in the digestive system, it receives the food by ingestion, breaks it into small particles through mastication (chewing). It receives secretions from the salivary glands and mixes them with food. The oral cavity contains your teeth and tongue.
- The Pharnyx serves both the respiratory and digestive system, as a channel for air and food. It is a fibomuscular passageway the connects the nasal and oral cavities to the larynx and esophagus. The upper region, or the nasopharynx, serves no purpose in the digestive system. The middle region, or the oropharynx, is the first region food enters when it is swallowed. The laryngopharynx is the lower region, and it opens into both the esophagus and larynx.
- The Esophagus is a collapsible muscular tube that serves as a passageway from the pharnyx and the stomach. It passes through an opening in the diaphragm, called the esophageal hiatus, and then empties into the stomach. The muscular layers of the esophagus are normally pinched together at both the upper and lower ends by muscles called sphincters. When a person swallows, the sphincters relax automatically to allow food or drink to pass from the mouth into the stomach.
- The Stomach receives food from the esophagus, and is located in the upper left quadrant of the abdomen. The stomach is divided into the fundic, cardiac, body, and pyloric regions. The lesser and greater curvatures are on the right and left sides, respectively, of the stomach. The gastric glands open to the surface of the mucosa through tiny holes called gastric pits. The secretions of the exocrine gastric glands - composed of the mucous, parietal, and chief cells - make up the gastric juice. The products of the endocrine cells are secreted directly into the bloodstream and are not a part of the gastric juice. The endocrine cells secrete the hormone gastrin, which functions in the regulation of gastric activity. Chyme is the semifluid mass of partly digested food expelled by the stomach. Relaxation of the pyloric sphincter allows chyme to pass from the stomach into the small intestine. The rate of which this occurs depends on the nature of the chyme and the receptivity of the small intestine.
- The Small Intestine extends from the pyloric sphincter to the ileocecal valve, where it empties into the large intestine. The small intestine finishes the process of digestion, absorbs the nutrients, and passes the residue on to the large intestine. The liver, gallbladder, and pancreas are accessory organs of the digestive system that are closely associated with the small intestine.
- The Large Intestine is larger in diameter than the small intestine. It consists of the colon, rectum, and anal canal. Chemical digestion is completed in the small intestine before the chyme reaches the large intestine. Functions of the large intestine include the absorption of water and electrolytes and the elimination of feces.
- The Rectum ends about 5 cm below the tip of the coccyx, at the beginning of the anal canal.
- The Anus, isthe last 2 to 3 cm of the digestive tract is the anal canal, which continues from the rectum and opens to the outside at the anus.
- The Salivary Glands produce your saliva. Saliva contains water, mucus, and enzyme amylase. Functions of saliva include the following: It has a cleansing action on the teeth, It moistens and lubricates food during mastication and swallowing, It dissolves certain molecules so that food can be tasted, and It begins the chemical digestion of starches through the action of amylase, which breaks down polysaccharides into disaccharides.
- The Liver is the largest gland in the body. The liver has a wide variety of functions and many of these are vital to life. Liver functions include the following: secretion, synthesis of bile salts, synthesis of plasma proteins, storage, detoxification, excretion, carbohydrate metabolism, lipid metabolism, protein metabolism, and filtering.
- The Gallbladder's main function is to is to serve as a storage reservoir for bile. Bile is a yellowish-green fluid produced by liver cells. The main components of bile are water, bile salts, bile pigments, and cholesterol.
- The Pancreas has both endocrine and exocrine functions. The endocrine portion consists of the scattered islets of Langerhans, which secrete the hormones insulin and glucagon into the blood. The exocrine portion is the major part of the gland. It consists of pancreatic acinar cells that secrete digestive enzymes into tiny ducts interwoven between the cells.
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