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Anatomy and Function of the Rectum

Rectum is a part of the lower digestive tract that enables the temporary storage of feces. This story provides some information about its anatomy and function.
Praseeda Shirodkar
No rule exists for the frequency of bowel movements. However, considering a healthy individual, the general range is from three times a day to three times a week.
The human digestive system is responsible for the process of digestion. The process of digestion has many stages, all of which are extremely important. One such important stage is the elimination stage that involves the removal of undigested food and waste products from the body. Here, the role or function of the rectum comes into play.

What is the Rectum?

The part of the alimentary canal from the sigmoid flexure to the anus is the rectum. It can also be referred to as the final portion of the large intestine that terminates at the anus.


The structure of the rectum can be understood with the help of the labeled diagram given here.


The digestive tract is a tubular passage that is about 8.3 meters in length, from the mouth to the anus. The last part of the digestive tract is the large intestine that is about 1.8 meters long, which includes the cecum, colon, rectum, and the anus.
The human rectum may have an average length of about 10-12 cm. As mentioned, it connects the sigmoid colon to the anus. The pelvic diaphragm which is a muscular sheet runs perpendicular to the joint connecting the rectum and the anal canal.
The rectum's internal cavity is divided into 3 or 4 chambers, each of which is partly sectioned from the others by permanent transverse folds. These folds aid in supporting the rectal contents. The outer wall of the rectum is surrounded by a covering of longitudinal muscle.
Organs such as the pancreas, spleen, liver, as well as the reproductive and urinary organs, are located close to the rectum. Due to this, conditions like colorectal cancer (involving both colon and rectum) that spreads outside the large intestine, can affect the neighboring organs.


The role of the rectum is to temporarily store feces until defecation.
The food that one consumes is first chewed in the mouth and as a part of the digestion process, has to pass through the stomach, small intestine, and lastly the large intestine.
The undigested food and waste products that are accumulated during the digestion process, move into the rectum in the form of fecal matter. It is the function of the rectum to receive this fecal matter and hold it till one defecates. Thus, the rectum stores fecal matter until defecation, during which the feces are eliminated from the body through the anus.

How it Works?

When the undigested food and other waste products in the form of fecal matter enter the rectum and make it full, the sensors signal this to the brain which further decides if defecation is possible.
Along with the brain, the impulses are also sent to the anal canal, chest, and muscles of the abdominal wall, thus, making one conscious about the need for stool evacuation.
If it is possible to evacuate, the sphincters relax and the rectum contracts, thus eliminating the fecal matter. If not possible, the sphincters contract and the rectum further holds the matter and causes the urge sensation to go away for some time.
If a person delays the defecation for a longer period, he/she may be affected by constipation. Thus, it is better to follow the bowel movements as and when one gets an urge to.
In case of certain diseases or problems that may be associated with the rectum, a rectal exam is conducted for diagnosis. Medical conditions like rectal cancer can be detected wit the help of endoscopy.