Your Digestive System and How it Works

How

The Digestive System
The digestive system contains many organs, and runs between your mouth and your anus. Image © A.D.A.M.

What Is The Digestive System?

Your digestive system does a lot of important work for your body. Food isn't in a form your body can readily use, so it's the digestive system that has to break it down into its parts. Through digestion, your body gets the nutrients it needs from foods and eliminates anything it doesn't need. This is a really basic overview of the digestive system, but obviously there's a whole lot more that goes into it that makes it all work.

And, unfortunately, this also means that things can pretty easily go wrong. For the purposes of this article, we are discussing a healthy digestive tract that hasn't been altered by surgery, such as colectomy, gallbladder removal, or resection.

How Long Is the Digestive System?

The digestive system can vary in length somewhat from person to person, but can be from about 25 to 28 feet long in most people, with some being as long as about 30 feet. The esophagus is about 9 to 10 inches in length, the small intestine is about 23 feet long, and the large intestine is about 5 feet long, on average.

How Long Does Food Digestion Take?

The time it takes for food to digest can vary a bit from person to person and between males and females. Studies have shown that the entire process takes about an average of 50 hours for healthy people, but can vary between 24 and 72, based on a number of factors. After chewing food and swallowing it, it passes through the stomach and small intestine over a period of 4 to 7 hours.

The time passing through the large intestine is much longer, averaging about 40 hours. For men the average time to digest food is shorter overall than it is for women. Having a digestive condition that affects transit time (the time it takes for food to pass through the digestive system) can shorten or extend the time.

Why Is Digestion Important?

We eat because we need nourishment, but our food isn't something our bodies can easily assimilate into our cells. It is digestion that takes our breakfast and breaks it down. Once it's broken down into parts, it can be used by the body. This is done through a chemical process, and it actually begins in the mouth with saliva. Once the components of food are released, they can be used by our body's cells to release energy, make red blood cells, build bone, and do all the other things that are needed to keep the body going. Without the digestive process, the body isn't going to be able to sustain itself.

From The Mouth To The Anus

The digestive system is one long tube that runs from your mouth to your anus. It's kind of gross to think of it that way, but that's exactly what it is. Now, there are valves and twists and turns along the way, but eventually, the food that goes into your mouth comes out of your anus. The hollow space inside the small and large intestines that food moves through is called the lumen.

Food is actually pushed through the lumen throughout the digestive system by special muscles, and that process is called peristalsis.

When you chew food and swallow, these are the structures in your body that the food goes through during its journey down to the anus:

  • Mouth. Food breakdown begins with chewing and the mixing of food with saliva. Once food is chewed sufficiently, we voluntarily swallow it. After that, the digestive process is involuntary.
  • Esophagus. Once food is swallowed, it travels down the esophagus and through a valve called the lower esophageal sphincter to the stomach.
  • Stomach. The stomach is where the rubber meets the road in digestion. There are digestive juices in the stomach that help break down the food and the muscles there mix the food up. After the stomach has done its job, there's another valve, called the pyloric valve, that allows food to move from the stomach and into the first part of the small intestine, which is called the duodenum.
  • Small intestine. Once food reaches the small intestine, it's mixed with even more digestive juices from the pancreas and the liver to break it down. The peristalsis in the muscles is still at work, moving everything through. The small intestine is where most of the nutrients are extracted from food. The intestinal walls absorb the vitamins and minerals. Anything that the body can't use or can't break down is moved through the entirety of the small intestine, through the ileocecal valve, and on to its next adventure in the large intestine.
  • Large intestine. The large intestine doesn't do much digesting, but it is where a lot of liquid is absorbed from the waste material. Undigested materials are moved through, which can take a day or more, and then into the last part of the colon, which is the rectum. When there is stool in the rectum, it precipitates an urge to defecate, and finally the waste materials are expelled out through the anus as a bowel movement.

Source:
Notghi A, Hutchinson R, Kumar D, Smith NB, Harding LK. "Simplified method for the measurement of segmental colonic transit time." Gut. 1994 Jul; 35:976–981.

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