Friday, January 28, 2011

Human Digestive System

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The Digestive System
The Human Digestive System consist of series of organs and structures that help break down the food and absorb nutrients fro through outthe body. Food enters th digestive system through mouth and passes to phyrnx to esophagus and then stomach where it half digested after it passes to Small Intestine here digetion completed and moves to large intestine and finaly expelled out through out he body. Other organs such as the liver, further aid in the break downof food, absortion of nutritions, and elimination of undigestible material from the body.




                                                         Mouth
The mouth plays a role in digestion, speech, and breathing. Digestion begins when food enters the mouth. Teeth break down food and the muscular tongue pushes food back toward the pharynx, or throat. Three salivary glands—the sublingual gland, the submandibular gland, and the parotid gland—secrete enzymes that partially digest food into a soft, moist, round lump. Muscles in the pharynx swallow the food, pushing it into the esophagus, a muscular tube that passes food into the stomach. The epiglottis prevents food from entering the trachea, or windpipe, during swallowing.


Pharynx
It is  muscular tube located in the neck, lined with mucous membrane, that connects the nose and mouth with the trachea (windpipe) and esophagus and serves as a passageway for both air and food. About 13 cm (5 in) long in humans, it lies in the front of the spinal column. The pharynx contains the tonsils and, in children, the adenoids. Because it begins in the back of the nasal cavity, the upper part of the pharynx is called the nasopharynx. The lower part, or oropharynx, refers to the area in the back of the mouth. The pharynx ends at the epiglottis, a flap of cartilage that prevents food from entering the trachea but allows it to enter the esophagus.




                                                             Esophagus
The presence of food in the pharynx stimulates swallowing, which squeezes the food into the esophagus. The esophagus, a muscular tube about 25 cm (10 in) long, passes behind the trachea and heart and penetrates the diaphragm (muscular wall between the chest and abdomen) before reaching the stomach. Food advances through the alimentary canal by means of rhythmic muscle contractions (tightenings) known as peristalsis. The process begins when circular muscles in the esophagus wall contract and relax (widen) one after the other, squeezing food downward toward the stomach. Food travels the length of the esophagus in two to three seconds.
 Stomach
Located on the left side of the body just below the diaphragm, the stomach is a muscular, elastic sac that connects the esophagus with the small intestine. Food enters the stomach through the esophagus. A muscle at the junction of the esophagus and the stomach, called the esophageal sphincter, prevents food from flowing back into the esophagus to cause heartburn. In the stomach three layers of stomach muscles (longitudinal, circular, and oblique) knead, toss, and churn the food, mixing it thoroughly with digestive juices secreted by the stomach lining. This process transforms the partially solid food mass into a semiliquid pulp that passes into the duodenum, the first part of the small intestine. Food is prevented from moving back into the stomach by a muscle known as the pyloric sphincter..
Small intestine
The small intestine is a coiled tube 6-m (20-ft) long that is located in the center of the abdominal cavity. It is the site where the majority of digestion occurs. Here secretions from the intestinal wall, bile duct, and pancreatic duct further break down food passed from the stomach so that nutrients can be removed and passed into the bloodstream. The lining of the intestinal wall is studded with millions of finger-like projections called villi that come into contact with liquefied food. Each villus is lined with absorptive cells that absorb nutrients from digested food. Beneath these cells lie a lymph vessel and a network of capillaries (tiny blood vessels) that carry nutrients from the small intestine to the cells of the body. Fatty nutrients pass into the lymph vessel, while sugars, amino acids, and other nutrients pass into the bloodstream and travel to the liver. Longitudinal and circular muscles encircle the intestinal tube and regularly contract to move food through the small intestine into the large intestine.
                                                         Large intestine

The small intestine is a coiled tube 6-m (20-ft) long that is located in the center of the abdominal cavity. It is the site where the majority of digestion occurs. Here secretions from the intestinal wall, bile duct, and pancreatic duct further break down food passed from the stomach so that nutrients can be removed and passed into the bloodstream. The lining of the intestinal wall is studded with millions of finger-like projections called villi that come into contact with liquefied food. Each villus is lined with absorptive cells that absorb nutrients from digested food. Beneath these cells lie a lymph vessel and a network of capillaries (tiny blood vessels) that carry nutrients from the small intestine to the cells of the body. Fatty nutrients pass into the lymph vessel, while sugars, amino acids, and other nutrients pass into the bloodstream and travel to the liver. Longitudinal and circular muscles encircle the intestinal tube and regularly contract to move food through the small intestine into the large intestine.

Liver
The liver is the largest internal organ in the human body, located at the top of the abdomen on the right side of the body. A dark red organ with a spongy texture, the liver is divided into right and left lobes by the falciform ligament. The liver performs more than 500 functions, including the production of a digestive liquid called bile that plays a role in the breakdown of fats in food. Bile from the liver passes through the hepatic duct into the gallbladder, where it is stored. During digestion bile passes from the gallbladder through bile ducts to the small intestine, where it breaks down fatty food so that it can be absorbed into the body. Nutrient-rich blood passes from the small intestine to the liver, where nutrients are further processed and stored. Deoxygenated blood leaves the liver via the hepatic vein to return to the heart.