Anatomy of the gut
We call it the gut, the colon, the intestines, the bowels and the digestive system. But what is it?
The gut, or digestive system, is in the abdomen.
The digestive system is for absorption of nutrients from food and expulsion of the resulting waste.
It consists of the small intestine and the colon.
The small intestine (small bowel) is around 6 m long and roughly 2 cm wide.
The colon (large bowel or large intestine) is about 2 m long and 6-7 cm wide, ending in the rectum and the anus.
On top of its many folds are forests of tiny finger-shaped protrusions called villae. Together, the folds and the villae make the gut's surface area as big as two tennis courts.
How the bowel works
The digestive system works by propelling food through the intestines over 24 hours. Muscle contractions squeeze the food through the different sections of the intestine that are separated by bands of muscles (or sphincters) that act as valves.
The passage of food from one area of the intestines to another is coordinated so that food stays in a specific area for long enough for the gut to do a particular job—absorb fluids and nutrients, or process and expel waste.
The small intestine (small bowel)
There are 3 parts of the small intestine: the duodenum, the ileum and the jejunum.
Food passes from the stomach into the duodenum, which is the tube that leads from the stomach into intestines.
The food then passes through the ileum and jejunum before going to the colon (large bowel). The small intestine absorbs nutrients and much of the liquid from foods.
The colon, or large intestine (also known as the large bowel), starts at the final portion of the small intestine and goes all the way to the rectum.
This muscular tube is made up of the ascending colon, where it meets the small intestine, the transverse colon, and the descending colon which ends at the rectum and then anus.
The colon’s main work is to store, process and expel waste. (The colon also absorbs some nutrients and water.) The rectum can store waste but most of the time it’s empty. Waste is expelled through the anus.