Anatomy of large intestine
The large intestine is the last part of the gastrointestinal tract. Its primary function is to absorb water from the undigested material that have to be passed out of body through the process of defecation in the form of feces. Before defection, the feces is stored in the rectum for time being and is defecated on the reflex. If the water is absorbed too much in the large intestine, it leads to constipation. The other condition is known as diarrhea in which water absorption is too low. There are many mucous glands known as goblet cells that lubricate the large intestine for the easy passage of undigested material. In this article, the discussion will be about anatomy of the large intestine mainly about its structure.
Location of the large intestine:
In humans, the large intestine starts from the right iliac region of the pelvis where it is joined to small intestine through its blind end cecum, the joining surrounded by the ileocecal valve. Then the cecum turns into the upward direction towards the abdomen known as ascending colon, when the colon passes across the width of the abdominal cavity forms the transverse colon, then the colon descends down to form the descending colon moving towards rectum and anus that is the end point of the large intestine. In humans, the large intestine is about 1.5 metres long that is about 1/5th of the whole GIT.
Parts of the large intestine:
The large intestine is consisted of the following five parts:
- Ascending colon; includes cecum and appendix too
- Transverse colon
- Descending colon
- Sigmoid colon; the S-shaped region of the large intestine leading to the rectum (storage site for feces)
Some parts of large intestine are retroperitoneal such that they are not completely covered by the peritoneum (abdominal-covering of tissue) and are thus immobile or fixed. These are:
- Ascending colon
- Descending colon
The parts of large intestine that are intra-peritoneal may be completely covered by the peritoneum and these parts can move. These include:
- Transverse colon
- Sigmoid colon
Cecum and appendix:
It is the first part of the large intestine and is also known as the blind end. It contains appendix as a gut associated lymphoid tissue. Colon is involved in digestion but the appendix is not. Appendix is said to inhabit the intestinal micro-flora that are beneficial to the human beings. But the main function of appendix is not clear yet. It has also been found to be riched in lymphatic cells in large number.
Ascending colon is the first part of the large intestine and is connected to the small intestine by ileocecal valve through cecum. It is about 8 inches and runs upward through the abdominal cavity toward the transverse colon. The main function of the ascending colon is to absorb water and other important nutrients from the undigested material and this material move towards the transverse colon by perisralsis.
Transverse colon is the second part of the large intestine. It is mobile being intra-peritoneal. It is sttached to the posterior abdominal wall through the mesentery which is known as transverse mesocolon. Transverse colon is below the stomach and is attached to it. From the front, it is covered by the large fold of the peritoneum known as greater omentum thus it is intra-peritoneal as it is covered by peritoneum as a whole. It starts from the hepatic flexure (the turn of the large intestine by the liver) and ends at the splenic flexure (the turn of the colon by spleen). The blood supply to this region is by the middle colic artery.
It starts from the splenic flexure and goes up to the beginning of the sigmoid colon. It is retroperitoneal and is immobile. Its prime function is to store and pass the feces to the rectum. The blood supply to descending colon is through the left colic artery.
Sigmoid colon is the S-shaped region of the colon and is next to the descending colon. The walls of the sigmoid colon are muscular in nature that contracts to move the feces into the rectum by increasing pressure. It is mobile as it is intra-peritoneal. The blood supply is by the sigmoid colon.
It is the last part of the large intestine in which the stool is stored till defecation.
So, in a nutshell large intestine is an important part of digestive system that has its main function as the absorption of water and nutrients.