The ascending colon is one of the four major regions of the colon, which is itself one of the parts of our large intestine. The ascending colon carries feces from the cecum superiorly along the right side of our abdominal cavity to the transverse colon. In the ascending colon, bacteria digest the transitory fecal matter in order to release vitamins. The intestinal wall absorbs water, nutrients, and vitamins from the feces and deposits these materials into our bloodstream.
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The ascending colon is a hollow tube about 2.5 inches in diameter and about 8 inches long, with many small pouches along its length to increase its surface area. The inferior end of the ascending colon connects to the cecum of the large intestine in the right iliac region of the abdominal cavity. From the cecum, the ascending colon rises superiorly toward the right inferior border of the liver. Just before reaching the liver, the ascending colon turns about 90 degrees to the left at the hepatic flexure. From the hepatic flexure the colon continues onward as the transverse colon.
About 90% of the nutrients present in digested food have been absorbed by the time it reaches the large intestine. This food is mixed with bacteria in the cecum to form feces. Waves of peristalsis move the feces slowly up the length of the ascending colon. As the feces pass through the ascending colon, bacteria digest the waste material that the human body cannot digest and liberate vitamins K, B1, B2, and B12. The walls of the colon absorb these vitamins along with most of the water present in the feces. Under normal conditions fecal matter enters the colon as chunky liquid waste and exits the colon as a condensed solid waste. The absorption of water by the colon helps to maintain water homeostasis in the body and prevent dehydration.
The mucosa forms the innermost layer of the ascending colon. Mucosa is made of epithelial tissue and secretes mucus from goblet cells to lubricate feces passing through the lumen. The cells of the mucosa absorb the vitamins and water from feces and transfer these substances to blood in nearby capillaries. Deep to the mucosa is the submucosa layer that contains the blood vessels, nerves, and connective tissues that support the mucosa. Next, the muscularis layer surrounds the submucosa and provides several layers of smooth muscle tissue to move food through the colon via peristalsis. The pouches of the colon are formed by the contraction of smooth muscle in the muscularis. The outermost layer of the ascending colon is covered by the peritoneum on the anterior side and by areolar connective tissue on the posterior side. These tissues hold the colon in place, provide blood vessels to the colon, and protect the colon from friction caused by the body’s movement.
Prepared by Tim Taylor, Anatomy and Physiology Instructor