WHAT ARE THE FOUR PARTS OF THE COLON?
The colon is made up of four sections that form a large loop that looks like a distorted "m" (see the picture below). The first section, which travels upwards, is called the ascending colon. The beginning part of the ascending colon is called the cecum. This is located in the lower right side of the belly. The ascending colon moves upwards to a sharp bend (known as the hepatic flexure) located below the liver. The liver is the largest organ in the body and is responsible for filtering (removing) harmful chemical substances, producing important chemicals for the body, and other important functions.
The colon is the major part of the large intestine, which is located in the belly. The intestine is a tube shaped structure that is part of the digestive tract. The colon is attached on the top end to the cecum, which is the first part of the large intestine. The colon is attached on the bottom end to the rectum, which is the last part of the large intestine. The large intestine absorbs moisture from the matter that is left after it is digested in the small intestine, and excretes the waste from the anus (rear end). Excrete means to release from the body as waste.
WHAT DOES THE COLON DO?
By the time digested material enters the colon, the process of digestion has been finished and the material is in a liquid form. One function of the colon is to absorb water and some types of salts from the digested material that passes through it. More specifically, the water and salts are absorbed into the blood vessels located in the third layer of muscles (known as the submucuous coat) in the colon. By absorbing almost all of the water and salts, the colon helps pack the digested material together so that in can later be passed out of the body as feces. The functions of the colon can impaired by conditions affecting it, such as colitis (inflammation of the colon).
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The hepatic flexure (see last paragraph) marks the second part of the colon, which travels across the belly. Because this part of the colon transverses (travels across) the belly, it is known as the transverse colon. The transverse colon passes below the stomach to the spleen on the left side of the belly. The spleen is an organ in the belly that helps fight infection. When the colon gets to the left side of the belly, there is a sharp bend downwards (known as the splenic flexure) that is the beginning of third section, known as the descending colon.
The descending colon passes down the left side of the belly to about the top of the hips. At this point, the colon is shaped like an "s" and for this reason is known as the sigmoid colon (sigma is the Greek name for the letter "s"). At the lower left side of the belly, the sigmoid colon connects with the rectum, which is the last part of the large intestine. The sections of the colon that were just discussed can be seen in the picture to the right:
WHAT ARE SOME OTHER CHARACTERISTICS OF THE COLON?
Overall, the colon is about 4.5 feet long and 2.5 inches wide. It is a muscular tube with a wet inner lining. The outer layer of the colon (known as the serous coat) is a tough tissue with a smooth surface on the outside. The toughness of the outer layer helps to protect the colon when its movements cause it to rub against the wall of the belly. The outer layer of muscles is made of three bands of muscles that run lengthwise. The inner layer of the colon has circular muscles. When these muscles shorten in a regular pattern of movement (a process known as peristalsis), it squeezes the contents that are inside (such as digested food) through the colon.
Inside the muscular coat of the colon is a layer called the submucous coat. This layer contains connective tissue, blood vessels, and lymphatic vessels. The segments of the colon give it an irregular appearance. Lymphatic vessels are structures that lymph travels through. Lymph is a milky fluid that contains proteins, fats, and white blood cells (which help the body fight off diseases).
The most inner layer of the colon is called the mucous coat. The mucous coat contains many tube shaped structures that produce large amounts of a thick, slippery fluid known as mucous. The mucous wets the inside of the colon where the digested material passes through. The mucous coat of the large intestine, unlike the small intestine, are not folded into villi (more than one villus). In general, a villus is a tiny, thin, fingerlike structure with a blood supply that sticks out from the surface.
WHAT IS THE ORIGIN OF THE WORD "COLON"?
Colon comes from the Greek word "kolon" meaning "large intestine."