Overview of the Human Digestive System

Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

Discover how the human digestive system works - one of the most important systems in the human body. Learn what each part does, and then see how much you remember with a quick quiz.

What is the Human Digestive System?

We all love food. It's tasty, and fun, and absolutely vital for life. But have you ever wondered how your body turns all that yummy food into the stuff the body needs to work? The body needs energy, and it needs it in the form of glucose (sugar). So how do we get from complex food that contains lots of things that aren't sugar, to pure, sugary energy?

The system in your body that does this important job is called the digestive system. The digestive system is a set of organs, passageways, and glands that work together to process complex food into the simple molecules your body needs. The digestive system includes your teeth, mouth, esophagus, stomach, small intestine, large intestine and rectum. Let's go through each step in the digestive process one at a time.

The human digestive system
The Human Digestive System

The Teeth and Mouth

The first step in the process of digestion is the teeth and mouth. You put food in your mouth, and the first thing that happens is that it gets chewed and broken down into smaller parts. This is important, because it not only makes it easier to swallow, but it also increases the surface area of the food, making other parts of digestion function better.

Teeth break food into smaller pieces.
Teeth Break Food Into Smaller Pieces

One of those other parts is the mixing of food with saliva. Saliva contains enzymes which break down the cell walls of the food, and start breaking complex carbohydrates into simpler carbohydrates and sugars. When the food is sufficiently digested, we swallow it, and it goes through a tube called the esophagus until it reaches the stomach. A muscle just outside the stomach forces it inside, and will even work if you're upside down.

The Stomach

A lot of action happens in the stomach. Your stomach contains strong acids that break down the food further. It churns the food in the acid to form a mixture called chyme. Enzymes are also released by the stomach, which are particularly good at breaking down proteins in the food you ate. Food will often stay in the stomach for hours, until it reaches a creamy or liquidy consistency, before being gradually squirted into the next section - the small intestine. It can take anywhere from two to six hours for this to happen.

The process by which enzymes break molecules into smaller ones
The process by which enzymes break molecules into smaller ones

The Small and Large Intestines

The next part of the digestive system is the small intestine, which is a long, windy and thin tube that snakes its way around the lower part of your belly. Here the food is mixed with bile and other enzymes, which are created by the liver and pancreas, to break down the molecules in the food even further. Once the food has been turned into glucose, those molecules are absorbed by the wall of the small intestine and move into the blood, where they provide energy for the body. The small intestine also absorbs vitamins, minerals, simple fatty acids and amino acids. This is another slow, gradual process and takes 3-6 hours.

After the small intestine, the food continues to the large intestine, which arches over the top of the small intestine before heading down towards the rectum. The large intestine's first job is to absorb all the water and electrolytes (like salt) in the digested food. This is also where the remaining waste products dry out to form feces that will later be expelled through the anus. But this takes a long time - food can take 24-36 hours to travel through the large intestine.

And that's it: the long journey of every meal you eat, from your mouth until you flush it down the toilet. It might not seem all that exciting, but it's an amazingly complex process that you literally couldn't live without.

Other Parts: The Liver, Pancreas and Gallbladder

The liver, pancreas, and gallbladder are all parts of the digestive system that we haven't talked about yet. They have several jobs. Many of the digestive juices we talked about are produced by these organs. The liver produces bile, which is stored in the gall bladder until needed, and the pancreas creates all those enzymes we discussed. The pancreas also creates hormones, though this isn't part of digestion.

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