The Digestive System

THE DIGESTIVE SYSTEM

The digestive system consists of a series of hollow organs joined in a long twisting tube from the mouth to the anus. Inside this tube is a lining called the Mucosa (this produces mucus and on underlying smooth muscle layers that contract to move food). There are two solid organs the liver and the pancreas; these produce digestive juices that reach the intestine through small tubes. Digestion is the process by which food and drink are broken into their smallest parts so that the body can use them to build and nourish cells to provide energy. Digestion begins in the mouth, where food is chewed into smaller pieces and then swallowed.

The large hollow organs of the digestive system contain muscle that enables their walls to move. The movement of the organ walls can mix food and liquid within each organ. The movement of the esophagus, stomach, and intestines is called Peristalsis (contraction of the smooth muscle of the gastrointestinal tract that propels food through it). Major muscle movement begins when food or liquids are swallowed. Although we are able to start swallowing by choice, once the swallow begin it becomes involuntary and proceeds under the control of the nerves.

Swallowed foods are then pushed into the organ called the Esophagus (flexible, muscular tube that moves food from the pharynx to the stomach). At the junction of the esophagus and stomach there is a ring like valve closing the passage between the two organs However as the food approaches the closed ring the surrounding muscle relax and allow food to pass.

The food then enters in what we call the Stomach (a dilatation of the alimentary canal of a vertebrate communicating interiorly with the esophagus and posterior with the duodenum). The stomach is a curve like organ, this organ has three mechanical task. First the stomach stores the food that has been swallowed then it mixes up the food, liquids, and digestive juices produced by the stomach. And finally it empty the contents into the Small Intestine (the part of the intestine that lies between the stomach and colon, consists of duodenum, jejunum, and ileum, secretes digestive enzymes, and is the chief site of the absorption of digested nutrients -- called also small bowel). Finally all of the digested nutrients are absorbed through the intestinal walls. The waste product of this process include undigested parts of food know as fiber, and older cells that have been shed from the mucosa. These materials are propelled into the Large Intestine (the more terminal division of the vertebrate intestine that is wider and shorter than the small intestine, typically divided into cecum, colon, and rectum, and concerned especially with the resorption