Digestive Tract

Many people are afflicted with problems in their digestive system. Wikipedia has this to say about the digestive tract.

The human gastrointestinal tract is the stomach and intestine, sometimes including all the structures from the mouth to the anus. (The "digestive system" is a broader term that includes other structures, including the accessory organs of digestion).
In an adult male human, the gastrointestinal (GI) tract is 5 metres (20 ft) long in a live subject, or up to 9 metres (30 ft) without the effect of muscle tone, and consists of the upper and lower GI tracts. The tract may also be divided into foregut, midgut, and hindgut, reflecting the embryological origin of each segment of the tract.
The GI tract always releases hormones to help regulate the digestion process. These hormones, including gastrin, secretin, cholecystokinin, and grehlin, are mediated through either intracrine or autocrine mechanisms, indicating that the cells releasing these hormones are conserved structures throughout evolution.
The upper gastrointestinal tract consists of the esophagus, stomach, and duodenum. The exact demarcation between "upper" and "lower" can vary. Upon gross dissection, the duodenum may appear to be a unified organ, but it is often divided into two parts based upon function, arterial supply, or embryology.
The lower gastrointestinal tract includes most of the small intestine and all of the large intestine. According to some sources, it also includes the anus.

Here are links to science articles about the digestive tract.

Scientists have discovered that important 'good' bacteria arrive in babies' digestive systems from their mother's gut via breast milk.

The results, featured in the current issue of Proceedings of the National Academy of the Sciences, show that the havoc inflammatory bowel diseases wreaks on the digestive tract is mirrored in bone marrow. Early indications also show that the disorders of the gut could potentially be treated through the bone marrow, said Pam Fraker, MSU University Distinguished Professor of biochemistry and molecular biology.

Colonoscopy saves lives, according to a study that provides the first direct evidence that the procedure keeps people from dying of colon cancer, reducing that risk by half. The research, reported yesterday in the New England Journal of Medicine, found that removing precancerous polyps spotted during a colonoscopy, a standard procedure today, dramatically cuts the chance of dying from the disease. The study followed 2,602 patients who had the suspicious growths removed during the test over a median of 15.8 years.