What are the parts of digestive system? How does digestion occur? The arrengement of the parts of digestive system.
Every living cell in your body uses food. But only dissolved food can get into your blood and then into your cells. Before food can be used in your body, it must first be made into a solution. Water dissolves some foods, but it does not dissolve all foods. Your body must change most of the food that you eat into other compounds that will dissolve. Digestion changes your food chemically and dissolves it.
A long tube goes from the mouth to the anus at the lower end of the body. This is the food tube, or alimentary canal, which is about 30 feet long. Notice that the tube does not have the same diameter throughout. Most of it is coiled up inside the abdomen. The alimentary canal is lined with alayer of special cells that give out a slimy material called mucus. You can feel this material on the inside of your mouth. Mucus lubricates the food tube so that materials can pass through it more easily. Connected with the alimentary canal are various digestive glands. These organs of the body give out digestive juices, which are mixtures of chemicals and water. The digestive juices change food and help dissolve it.
In the mouth, the teeth cut and grind the food into tiny bits.
While the food is being chewed, it is also mixed with saliva. This digestive juice is given out by the salivary glands, which are connected with the inside of the mouth by little tubes, or ducts. Saliva moistens and lubricates the food so that it can be swallowed more easily. When food is swallowed, it goes from the mouth through a passageway called the pharynx into the gullet, or esophagus. This is about an inch in diameter and 10 inches long. Circular muscles working automatically in the walls of the esophagus cause wavelike motions that push the food along. The muscles above the food contract, while those below the food relax. This keeps on until the food is pushed into the stomach, which is just below the diaphragm.
The stomach is a pear-shaped part of the alimentary canal, and it holds about 3,5 pints. So it is a good place to store a meal. In the lining of the stomach are millions of tiny pitlike gastric glands that give out gastric juice, which helps digestion. Outside the lining of the stomach are three layers of muscles. As these muscles contract and relax automatically, they keep churning the food inside. if you keep closing and opening your hand on a mixture of crackers and water, the crackers will become a pulpy, half-liquid mass. Something like this happens in the stomach as food is broken into tiny bits and mixed with gastric juice. From 1 to 4 hours after food is eaten, it is emptied from the stomach into the small intestine.
The small intestine is the most important part of the alimentary canal.
It is also the longest part. Though the small intestine is only about an inch in diameter, it is more than 20 feet long. Connected with the upper end of the small intestine by little tubes are two important glands, the liver and the pancreas. The liver gives out bile, while the pancreas gives out pancreatic juice. The tube from the liver is also connected to a kind of sac called the gall bladder. Bile is stored in the gall bladder when it is not needed in the small intestine. Tiny glands in the lining of the smaIl intestine give out a digestive juice, called intestinal juice. Bile, pancreatic juice, and intestinal juice are all mixed with the food as it is chumed back and forth by muscles working automatically in the walls of the small intestine.
Wavelike motions siınilar to those in the esophagus gradually push the food along in the small intestine. Food takes from 3 to 6 hours to travel through its entire length. By the time the food reaches the lower end of the small intestine, everything that can be digested has usually been chemically changed and dissolved. The digested food goes into the blood. The undigested part of the food and a good deal of water mixed with it are then pushed on into the large intestine. This part of the digestive tract has alarger diameter than the small intestine. The smaIl intestine, is only about 1 inch in diameter.
The large intestine, however, is nearly 2.5 inches in diameter. The small intestine is more than 20 feet long. But the large intestine is less than 6 feet long. In the large intestine, extra water from the worked-over food is absorbed so that the body does not lose it. Undigested food and other waste materials are gradually pushed along toward the lower end of the large intestine. From time to time, these waste materials are passed out of the body.