Colitis

Colitis is inflammation of the inner lining of the colon and is associated with diarrhea, pain, and blood in the stool. There are numerous reasons for the colon to become inflamed including:

• infection,
  
  
• loss of blood supply to the colon,
  
  
• inflammatory bowel disease, and
  
  
• invasion of the colon wall with collagen or lymphocytic white blood cells.

Anatomy of the colon

The colon is a hollow, muscular tube that receives products of digestion from the small intestine and ultimately eliminates them from the body through the anus. The colon is located in the abdomen and has numerous sections that are named based on their location. Colitis can affect different sections of the colon.

• The colon begins in the right lower abdomen with the cecum (located just above the appendix) into which the products of digestion empty from the small intestine.
  
  
• The ascending portion of the colon then ascends from the lower to the upper right side of the abdomen.
  
  
• It traverses the abdomen as the transverse portion of the colon from the right upper to left upper abdomen before descending from the upper to the lower left side of the abdomen.
  
  
• The last portions of the colon are the sigmoid colon low in the abdomen and finally the anus.

The colon also has several layers. The mucosa (inner layer or lining) comes into contact with the products of digestion and fluid and actively removes water and electrolytes to help solidify the feces. A layer of smooth muscle (a special type of muscle) surrounds the inner layer and is responsible for squeezing and mixing the undigested food and transporting it through the length of the colon to the anus.

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