The colon is one of the main organs of the digestive system. It helps the body absorb water and nutrients from food before excreting the waste. It is made up of muscle and located just below the stomach.

People mistakenly refer to the colon as the large intestine, but it is only one section of the large intestine. The other sections are the appendix, cecum, and rectum.

In healthy people, the colon looks like a U-shaped tube that is about 5 feet (1.5 meters) long. It makes up one-fifth of the length of the digestive tract, which begins at the mouth and ends at the anus.

In this article, we explain the colon’s function, its parts, and what each part does.

An engraved anatomical drawing of the colon in blue ink.Share on Pinterest
Photo editing by Stephen Kelly; Photography courtesy of Cecilia Grierson/Wikimedia

As a person eats, the small intestine digests and absorbs up to 90% of the nutrients that become fuel. What remains then passes to the colon.

The main role of the colon is to process indigestible food material.

More specifically, the colon:

  • absorbs water
  • absorbs electrolytes, such as potassium and chloride
  • absorbs vitamins
  • forms and pushes feces to the rectum for excretion

The colon is uniquely capable of breaking down indigestible matter because it hosts large populations of microorganisms, including bacteria, fungi, and archaea. Together, these contribute to the gut microbiome.

The microbiome is essential for digestion, and it helps generate nutrients that the body needs. The populations of microorganisms also influence immunity.

Learn more about the microbiome in our dedicated hub.

The colon is made up of five parts:

  • the cecum
  • the ascending colon
  • the transverse colon
  • the descending colon
  • the sigmoid colon

Click on the body map above to interact with a 3D model of the colon.

The cecum, pronounced “see-kum,” is also called the “proximal right colon.”

It is a small pouch that measures about 6 by 9 centimeters (cm), or about 2.3 by 3.5 inches (in). The cecum is held by a thin membrane known as the peritoneum.

This pouch connects the small intestine to the rest of the colon. Partially digested food comes into the cecum from the small intestine before entering the ascending colon.

The cecum is also connected to the appendix, a worm-like structure near the lower part of the cecum.

Scientists do not fully understand the role that the appendix plays. It may be a remnant of human evolution that no longer serves a purpose, but a 2017 study suggests that the appendix may act as a reservoir for helpful gut bacteria.

The ascending colon is the second part of the large intestine, continuing from the cecum. It is about 20–25 cm (7.8–9.8 in) long and is located behind the peritoneum.

The ascending colon gets its name from the fact that it is vertical, pushing material up the right side of the abdomen.

The ascending colon has two key functions. It absorbs the remaining water and nutrients from indigestible matter then solidifies it to form stool.

The transverse colon is the longest and most mobile part of the colon. It runs from the right to the left of the abdomen and connects the end of the ascending colon to the start of the descending colon.

The main role of the transverse colon is to absorb water and salts from indigestible food matter.

As its name suggests, the descending colon moves waste downward. It begins at the end of the transverse colon and moves material down the left side of the abdomen. It is about 10–15 cm (3.9–5.9 in) long.

The descending colon stores stool before this moves to the next compartment — the sigmoid colon.

This is the last part of the colon. It looks like an S-shaped tube that hangs off of the descending colon and leads to the rectum.

The job of the sigmoid colon is to solidify stool before it enters the rectum and anal canal for excretion. It does this by contracting, and the increased pressure moves the stool.

The sigmoid colon also absorbs water and salts from waste matter, though it does this to a lesser extent than other parts of the colon.

The paracolic gutters are spaces between the colon and abdominal wall. They allow infectious fluid to travel out of the organs in the gut.

There are two paracolic gutters, one on either side of the body. The right lateral paracolic gutter is a wide space between the ascending colon and the abdominal wall.

The left lateral paracolic gutter is narrow by comparison. It is located to the side of the descending colon.

Doctors cannot see the paracolic gutters with medical imaging tests, such as X-rays. However, as 2016 research points out, the spaces become visible when a disease affects the area, such as one that produces a tumor.

The colon has many functions, and it plays a vital role in digestion and waste excretion. It has five parts, each of which absorbs water and nutrients, solidifies stool, and moves waste toward the rectum.

The colon is also home to most of the gut’s microorganisms, which help break down material that the body could not digest on its own.

Scientists are still learning about the functions of some parts of the colon, such as the appendix and paracolic gutters.