Where are the colon and rectum? What do they do, exactly?

Lower intestine. The colon and rectum are the lower end of the gastrointestinal (GI) tract that starts in the mouth. The colon's main function is to absorb water, although a variety of other subtances may be absorbed through the colon, as well. It acts as a reservoir function so that most people have only 1 or 2bm's each day. The rectum is the lowest end. It has muscles and nerves that give bowel control.
LGI anatomy lesson. The colon (large intestine) is the last five feet of the GI tract. Simplistically, the right colon scavenges water to prevent dehydration, the left colon stores solid waste. The rectum samples intestinal contents, assists in stool continence, and through a series of coordinated neurologic steps permits colonic emptying.

Related Questions

Can too much tea (or coffee) aggravate the colon and rectum to where it bleeds?

It's Wpossible. But not likely. The caffeine in tea and coffe often stimulates the bowel, but rarely causes enough irritation to cause bleeding. Watch stools for further bleeding, if persistent, need to see health care provider.
Caffeine. Hello, too much of anything isn't always a good thing. It (caffeine) would probably have little to do with the bleeding you are describing. See your doctor.

Could impacted stool in large colon and rectum cause black stools?

Not likely. From the standpoint of the medical profession, black stools -called melena - are always assumed to be blood. Usually representing bleeding from stomach or "higher up" within the intestines. Colon bleeding usually is red. Unfortunately, bismouth containing medications can also cause black stool, but even with that type of product, one cannot be sure there is not bleeding also. Needs evaluation.

Can impacted stool in large colon and rectum cause black stools? What are your expert opinions?

No. Darker but not black. Black stool can be from blood entering and mixing in the stool high up in the GI tract notably stomach and duodenum. Black can also be from iron pills and high iron intake in consuming a lot of high iron meals like spinach and green leafys. East to rule out blood with a simple smear at the doctors office. That's my advice.