Mini Lesson: Large Intestine

Video Transcript

The final part of the digestive tract is the large intestine, also known as the colon, where the body is no longer breaking down food. By this point, fats, carbohydrates, and proteins should have been broken down as much as possible by the stomach acid and enzymes, and then taken into the body with various vitamins and minerals.

Role in Hydration

The large intestine is mostly in charge of absorbing water and minerals from what is left of the food that has been digested. When the cells in the digestive tract send the acids and enzymes to break apart the food, there is also a lot of water that is used to help break apart the different molecules in food. Some of the water is taken back in by the cells of the stomach and quite a bit in the small intestine, but the large intestine is really responsible for taking up the rest of the water that the body needs. This makes sure that there is enough water to help all of the chemical reactions needed to break down foods, but that the water is not lost. This is really important, since your entire body needs that water. Without the large intestine reabsorbing it, you would need to be drinking a LOT more water during the day.

When the cells of the large intestine take in the water, they also take in electrolytes. These are special forms of minerals that have a lot of important jobs in the body. Perhaps one of the most important is to help keep water balanced in the body, so it makes sense that they get taken in together in the large intestine.

Microbiome

Another major job for the large intestine is to provide the environment for little organisms like bacteria to live. Even though the body is done breaking down food as much as it can, there will still be fiber left from plant foods since our enzymes cannot break them down. The fiber becomes food for many different types organisms. When they break down the fiber, they make lots of different molecules that are helpful for the cells of our large intestine, and the rest of our body, too. 

Since the large intestine does not make its own enzymes to break down food, it is really counting on the mouth, stomach, small intestine, and accessory organs to do their job. If foods that have not been broken down properly reach the large intestine, they provide different types of food for the little organisms living in the large intestine. Since all the different organisms like to eat different things, this means that there would be fats, proteins, and starches to feed the bacteria that normally don’t get much to eat, since those are typically digested earlier in the body. As they eat and grow, they start to change how this little community of organisms works together, crowd out the good bacteria, and change how much of those helpful molecules are made.

Importance of Fiber

These helpful molecules that are made when good bacteria break down fiber may help to keep cancer cells from growing in the large intestine, which is one reason that eating lots of different types of fiber may help to protect against cancer. But when these bacteria get crowded out, less of these molecules means weaker cells that are likely to get damaged, experience inflammation, and potentially cause pain or the growth of cancer.

Eating fiber is also important to help the body get rid of toxins. Though the liver is in charge of boxing up the toxins in bile, fiber from our food grabs on to the bile and toxins to make sure that they leave the body with feces. But changes in that bacterial community can mean there are more bacteria that specialize in separating the fiber from the bile and toxins, which means they can get reabsorbed back into the body. Dealing with these toxins for a second or third time means that the liver needs a lot more nutrients to take care of the problem.

Motility

One final problem to think about is how quickly food passes through the digestive tract, especially the large intestine. Though it’s not always the large intestine’s fault, this is where we can experience issues of diarrhea or constipation. Sometimes the issue is further up the digestive tract and the large intestine just gets stuck with the problem, but there may also be changes to that bacterial community in the large intestine that cause these problems as well.