Rectum

The straight part of the colon is the dilated pouch like structure that is preceded by sigmoid colon and followed by anal canal. Before you defecate, the feces is temporarily stored in this gastrointestinal structure which becomes dilated on the arrival of waste material and induces the urge for its elimination through anal verge. The word "rectum" has been derived from a Latin phrase "Rectum Intestinum" which means "straight intestine". As the rectum facts suggest, this organ is about 12 cm in length, and begins at the third sacral vertebrae and is joined with the preceding section of large bowel at rectosigmoid junction. Based on the structure and function of the distal end of large gut, you can divide rectum parts

The primary rectum function is the temporary storage of stool so that you may have some time to reach the place where it can be defecated. As the waste and indigestible materials get entry into it, the canal becomes dilated, thus stretching the muscles lining the rectal region. Stretch receptors are located in the wall of rectum which sense the dilation of the gut and send signal to the nervous system (brain) where these are processed and a response is generated that induces the need for the elimination of waste materials passing through anal canal and getting out through anal verge. However, if you do not go for defecation for a prolonged duration, the stool gets back into the colon for further absorption of fluids which may also result in hardening of stool and constipation.