The Digestive System (cont.)

Also called the throat, the pharynx is the portion of the digestive tract that receives the food from your mouth. Branching off the pharynx is the esophagus, which carries food to the stomach, and the trachea or windpipe, which carries air to the lungs.

The act of swallowing takes place in the pharynx partly as a reflex and partly under voluntary control. The tongue and soft palate -- the soft part of the roof of the mouth -- push food into the pharynx, which closes off the trachea. The food then enters the esophagus.

The esophagus is a muscular tube extending from the pharynx and behind the trachea to the stomach. Food is pushed through the esophagus and into the stomach by means of a series of contractions called peristalsis.

Just before the opening to the stomach is an important ring-shaped muscle called the lower esophageal sphincter (LES). This sphincter opens to let food pass into the stomach and closes to keep it there. If your LES doesn't work properly, you may suffer from a condition called GERD, or reflux, which causes heartburn and regurgitation (the feeling of food coming back up).

The stomach is a sac-like organ with strong muscular walls. In addition to holding food, it serves as the mixer and grinder of food. The stomach secretes acid and powerful enzymes that continue the process of breaking the food down and changing it to a consistency of liquid or paste. From there, food moves to the small intestine. Between meals the non-liquefiable remnants are released from the stomach and ushered through the rest of the intestines to be eliminated.

Made up of three segments -- the duodenum, jejunum, and ileum -- the small intestine also breaks down food using enzymes released by the pancreas and bile from the liver. Peristalsis is also at work in this organ, moving food through and mixing it up with the digestive secretions from the pancreas and liver, including bile. The duodenum is largely responsible for the continuing breakdown process, with the jejunum and ileum being mainly responsible for absorption of nutrients into the bloodstream.

A more technical name for this part of the process is "motility" since it involves moving or emptying food particles from one part to the next. This process is highly dependant on the activity of a large network of nerves, hormones, and muscles. Problems with any of these components can cause a variety of conditions.

While food is in the small intestine, nutrients are absorbed through the walls and into the bloodstream. What's leftover (the waste) moves into the large intestine (large bowel or colon).

Everything above the large intestine is called the upper GI tract. Everything below is the lower GI tract.

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Source: MedicineNet.com
http://www.medicinenet.com/the_digestive_system/article.htm