The small intestine leads right into a 5 feet long large intestine which then ends in the anus, which is why the large intestine is the second last part of the digestive system. Although both the small and large intestines play major roles in carrying out digestion, their functions are very different.
While the small intestine is where majority of the digestion takes place, wherein most of the food gets absorbed, the function of the large intestine mostly pertains to absorption of water and excretion of solid wastes through the anus.
The large intestine is far larger than the small intestine and can be divided into 6 different regions; cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum.
Large Intestine Structure
Situated in the right lower abdomen, the cecum is a small, pouch-shaped structure that forms the first part of the large intestine. It is connected to the last portion of the small intestine (ileum) on its anterior end and the ascending colon at its posterior end.
The colon is the longest part of the large intestine and begins with the ascending colon, which is called so because it starts at the base of the abdomen (right side) and moves upwards towards the liver. It ends where the colon begins to turn beside the liver.
The ascending colon leads into the transverse colon that moves from right to left, across the abdomen. It lies just below the stomach. Moreover, the transverse colon is also attached to the stomach by a band of tissue called greater omentum. It then turns downwards at the spleen and ends into the descending colon.
Traveling downwards from the transverse colon is the descending colon which is situated on the left side of the abdomen, and ends into the last part of the colon called the sigmoid colon.
Situated at the bottom left side of the abdomen, the sigmoid colon is an 'S-shaped' structure joining the descending colon and the rectum. This portion of the colon is lined with strong muscle tissues, which give the colon the necessary strength to expel waste into the rectum.
The last portion of the large intestine is called the rectum. This is where waste materials are stored in the form of stool until they are excreted out from the anus. It consists of a thick mucosal lining and is supplied with many blood vessels.
Function of the Large Intestine
Now that we have understood the different parts of the large intestine, we can now move ahead to understand the function of each part. The digestion of food has already taken place in the small intestine, and only water and salt absorption takes place in the large intestine. Thus, the large intestine helps in maintaining the fluid balance of the blood.
At the point of union of the ileum and the cecum, there exists a valve or sphincter muscle which opens and pushes food from the ileum into the expanding cecum.
The cecum of the large intestine accepts the digested food from the small intestine and pushes it towards the ascending colon. The food received is undigested fiber from consumed food, some water, vitamins, minerals, and salts.
The cells of colon lining absorb most of the water, vitamins, and minerals from the mass of moisture and undigested food received from cecum. By muscular contractions, this undigested food or fecal matter is passed through the colon and into rectum. Eliminating toxic waste materials from the body in the form of stool is also a part of functions of the colon.
The rectum receives fecal matter from the sigmoid colon and stores it till it is excreted away via the anus (the last part of the digestive system).
Improper functioning can result in conditions such as green stool, irritable bowel syndrome, constipation, and Crohn's disease. Thus, the role that the large intestine plays is extremely crucial for our well-being.