Transverse Colon

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The transverse colon is the longest region of the colon and is located between the ascending colon and descending colon. It is named for the fact that it crosses the abdominal cavity transversely from the right side to left side just below the stomach. Much of the absorption and feces formation of the colon takes place in the transverse colon, making it a very important region of the digestive system.

Anatomy

The colon is the main portion of the large intestine and is divided into four regions: the ascending, transverse, descending, and sigmoid colon. The transverse colon begins at the hepatic flexure, a sharp bend at the superior end of the ascending colon just inferior to the liver on the right side of the abdominal cavity. At the hepatic flexure, the colon turns to the left and crosses to the left side of the abdominal cavity as the transverse colon. Upon reaching the left side, the colon again turns sharply toward the inferior direction at the splenic flexure before continuing on as the descending colon.

The transverse colon is a hollow tube about 2.5 inches (6 cm) in diameter and around 18 inches (46 cm) in length. It curves along its length so that the middle of the transverse colon is inferior and posterior to the hepatic and splenic flexures at its ends. Many pouches, or haustra, are formed in the walls of the transverse colon by contraction of the smooth muscle of the intestinal walls.

Histology

The walls of the transverse colon are made of four tissue layers: the mucosa, submucosa, muscularis, and serosa.

The mucosa is the innermost layer of epithelial tissue that borders the hollow lumen and is in contact with feces. Its name is derived from the mucus produced by goblet cells that line the surface of the mucosa to lubricate the transverse colon. Mucus protects the intestinal walls from friction as rough fecal matter passes along its length. The mucosa is also responsible for the absorption of nutrients and water from feces and the delivery of these substances to the bloodstream.

Deep to the mucosa is the submucosa layer that supports the other three layers of the intestinal wall. Many blood vessels and nerves travel through the submucosa to provide nutrients, oxygen, and nerve impulses to the tissues of the mucosa, muscularis, and serosa. Nutrients and water extracted from feces are also returned to the body through the veins of the submucosa.

The next layer, the muscularis, is made of several bands of smooth muscle that mix and move feces through the transverse colon.

Lastly, the serosa is the outermost layer of the transverse colon that acts as the skin of the colon. Just like the skin of our arms protects what is beneath it, the serosa protects the transverse colon from damage caused by its surroundings. The serosa secretes serous fluid, a thin, slick secretion that prevents friction between the transverse colon and the surrounding tissues.

Physiology

The transverse colon mixes feces by contracting small regions of the intestinal wall in a process known as segmentation. As the feces are mixed, bacteria ferment the waste material to release vitamins and a few trace nutrients remaining in the waste. Water, nutrients, and vitamins are absorbed through the walls of the colon to be used by the tissues of the body. The colon then uses slow longitudinal waves of muscle contraction known as peristalsis to push the feces along its length.