Digestive Tract from Cyber-Anatomy Web site and Think Quest
The mouth and teeth are the first organs of the digestive tract. The teeth are bones whose primary purpose is to grind food in to easy bits that the body can digest. In the mouth, saliva helps begin to break down food. There are certain organs that are located in the mouth, such as the uvula (the “thing” that hangs down in the back of your mouth) and the tongue. The walls of the inner cheeks are lined with mucous which help protect the food from bacteria, and also protect the cheeks form saliva.
The pharynx is the passage way through which many tubes run from the mouth and the nose to the upper body. Some of these tubes are the nasopharynx, which runs oxygen to the lungs, and the oropharynx, which also runs oxygen to the lungs.
The esophagus runs from the pharynx to the stomach. The Esophagus is about 25 cm ( 10 inches) long. The esophagus is really a large muscle which pushes food down to the stomach. The walls of the esophagus are lined with four layers of thin tissue. These membranes are, the mucosa, the submucosa, the muscularis externa, and the serosa.
The stomach is a J- shaped muscle. The stomach acts as a churn. There are two sphincters,circular muscles that act as valves placed outside organs, surrounding the two openings of the stomach. Chemical breakdown of food begins in the stomach.
The constant churning helps to improve digestion. There are several acids in the stomach. One of these acids is known as gastric juice. Gastric juice is manufactured in gastric glands located in the stomach. With gastric juice and other acids being mixed with the food, it breaks down and become a creamy substance known as chyme. After being transformed into chyme, it goes into the small intestine.
The small intestine is the primary organ of the of the digestive tract. In the small intestine, chyme is finally broken down for its passage to cells. Bile is added to aid in digestion of fats. Bile is manufactured in the liver. The small intestine may be subdivided into three segments. The first segment of the small intestine is known as the deudodenum. The deudodenum is about 25 cm ( 10 inches ) long. The second segment of the small intestine is known as the jejunum. The jejunum is about 2.5 meters ( 8 feet) long. The final segment of the small intestine is known as the ileum. The ileum is about 3.6 meters (12 feet ) long. Since the small intestine can only process a small amount of chyme at a time, the spchinter located at the beginning of the small intestine regulates theamount of food that enters the small intestine.
In addition to digesting chyme, the small intestine is responsible for absorbing the processed food into the bloodstream for delivery to the cells. This absorption takes place through structures known as villi. Villi are finger like projections that increase surface area for absorption. The unabsorbed chyme then passes to the large intestine.
The large intestine is about 1.5 meters ( 5 feet ) long. The large intestine stretches from a valve that rests between the end of the small intestine and the beginning of the large intestine to the anus. The main job of the large intestine is absorb water and to rid the body of any unwanted materials by sending it to the anus. The large intestine has many subdivisions such as the cecum, the appendix, the colon, the rectum, and the canal.