Large Intestine & Rectum

What is the Large Intestine

The large intestine is the continuation of the small intestine. It begins at the ileo-caecal junction and ends with the rectum and anal canal. It measures about a meter in length.

Where is the Large Intestine situated?
The large intestine lies in the lower part in the abdominal cavity and extends up to the pelvis. It is located behind the small intestine and lies above the posterior pelvic muscles. The large intestine runs along the border of the abdominal cavity at the top and ends as the rectum.

How can we describe the Large Intestine and Rectum?
The large intestine is divided into three major parts for the purpose of study. These are the :

• Caecum a short tube measuring about 6 cm. in length.
• Colon comprising of the ascending colon located on the right side of the abdominal cavity; The transverse colon which lies horizontally at the top of the abdominal cavity and the descending colon which comes down on the left side and becomes the rectum.
• Rectum which ends in the anal canal and anus through which feces are passed.
• The appendix is an important organ in relation to the large intestine. It is situated 2 cm. from the ileo-caecal junction. It is a vestigeal i.e. an organ without any function in the human body. Appendicitis is a common complaint due to entrapment of food particles in the appendix.

A similar vestigeal organ is the ileo-caecal valve, which is present at the junction of the ileum and the caecum. This only partially prevents the reflux of the contents of the large intestine into the ileum.

The large intestine when seen under the microscope shows a larger diameter than the small intestine. It shows:

1. Mucus layer : which is thinner than the small intestine without presence of any structures like the villi. But there are numerous pit-like structures, which help to absorb large amounts of water.
2. Submucosa
3. Muscular layer : which is also considerably thinner than that of the small intestine.
4. sa : a tough layer surrounding all other layers
5. ry : through which the nerves and blood vessels run.

The rectum is a short muscular tube, which has the same internal structure as the large intestine. It ends in the orifice called as the anus.

Functions of the large intestine

The function of the large intestine is to throw out the unwanted matter after digestion outside the body. The caecum has a short pouch that has a valve, which regulates the flow of chyme. The colon absorbs water from the feces. Along with the bacteria that reside in the colon, the total bulk of the fiber in the feces is thus reduced. This process can take up to two days. The feces reach the rectum, which is also, a hollow muscular tube and excreted through the anus. The rectum stores the dried, undigested feces for some period of time before their excretion.