Compared to the small intestines, the large intestines have almost twice the diameter but are only half as long. With regards to its function in the digestive system, the large intestine serves as the last remaining site to absorb traces of water from food residue, serves as a temporary holding facility for the indigestible food residue and then eliminates them out of the body in a semisolid form of feces.
Gross Anatomy of the Large Intestine
Haustra, teniae coli and the epiploic appendages are three features found in the large intestines but can never be found anywhere else. Teniae coli, it’s literal translation meaning ribbons of the colon, is the longitudinal muscle layer reduced to three bands of smooth muscles. The muscle tone of the intestinal walls of large intestine causes the formation of pocket-like sacs known as haustra. Upon closer inspection to the large intestines, small fat-filled pouches hang from its surface. These pouches are called epiploic appendages and until this very moment, their significant is still unknown.
Subdivisions of the Large Intestine
The large intestine can be subdivided into the appendix, cecum, rectum, colon and the anal canal. The first part of the large intestine is the cecum. It is a sack-like structure found in the right iliac fossa just below the ileocecal valve. Attached to the cecum is the vermiform appendix. The appendix plays an important role when it comes to body immunity but its structure is its downfall. The twisted appendix is an ideal place for bacteria to accumulate.
Another subdivision is the colon, which has several very distinct regions. The ascending colon is found on the right side of the abdomen, travelling up to the level of the right kidney. Upon reaching this height, it then makes a right-angle turn. This turn is called the right colic or the hepatic flexure. This part of the colon, now travelling across the abdomen, is called the transverse colon. As it reaches the point where the spleen is located, it makes another turn forming the left colic or the splenic flexure. It then continues to travel downwards, now on the left side. This part of the colon is now called the descending colon. The colon now then enters the pelvis, becoming the sigmoid colon.
The sigmoid colon then joins the rectum at the level of the third sacral vertebra. The anal canal, representing the last part of the large intestine, lies externally the abdominopelvic cavity. As it open to the body, it then is given another name, the anus. The sphincters function in the anal canal, the internal and external anal sphincter. The internal anal sphincter is an involuntary smooth muscle which is formed as part of the muscularis. The external anal sphincter on the other hand, composed of skeletal muscles, is a voluntary sphincter.
The haustra and the teniae coli are not found in the anal canal and the rectum. In order for the rectum to expel its contents, a strong contraction is provided by its well developed muscle layers.