How does the Digestive System Work?

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  • Written By: Michael Anissimov
  • Edited By: Niki Foster
  • Last Modified Date: 10 October 2019
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The human digestive system is a sequence of organs that use mechanical and chemical means to take in food, break it down, extract nutrients and energy, and eject waste products in the form of urine and feces. This system evolved incrementally over the course of hundreds of millions of years and is the only natural way for humans to obtain energy for movement and thinking. It is capable of handling a variety of food sources, both animal and vegetable, but tends to handle food best when it is cooked. Because cooked food has been around for so long, humanity as a species is slightly “spoiled” in its favor, and many people get sick if they consume food that has not received adequate cooking.

The mouth is the entrance to the human digestive system. Teeth gnash the food, breaking it down mechanically, while the three salivary glands release saliva containing the enzyme amylase, which breaks down starch and fat chemically. Saliva makes food easier to swallow by moistening it, as well as preventing the erosion of tooth enamel by modulating pH.

After entering the body at the back of the throat, food travels down the esophagus, being transported not by gravity but by muscular contractions. This is why it is possible to eat while hanging upside down. The interior of the esophagus is very moist, which helps to further break down food and prevent damage to the rest of the system.


After moving through the esophagus portion of the digestive system, food and drink reaches the stomach, where it is further broken down into manageable pieces. Because the nutrients in food are ultimately meant to be consumed by cells, they must be broken into very small parcels for delivery. The primary agent of digestion in the stomach is gastric juices, which are produced in large amounts and can be very acidic. A secondary agent is muscular contractions within the stomach.

After the stomach, the broken down food moves into the small intestine, the area where most of the nutrient extraction takes place. As the food moves through the small intestine, it is mixed with bile, which is produced by the liver, as well as pancreatic juices, which perhaps unsurprisingly come from the pancreas. These two liquids help further the digestive process, breaking down the nutrients in food to the point where it can be absorbed by the blood. The inner intestine is home to the famous villi, tiny living extrusions which gather nutrients on a fine scale.

The final components of the digestive system are the large intestine or colon, the anus, and the urinary tract, which separate the liquid matter from the solid matter and send them to their respective exit ports. Of course, the human digestive system is not 100% efficient, and there are many nutrients left over in this “waste”, which will be consumed happily by bacteria or sent through a waste processing plant.


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Post 50

So you mean there are still some undigested nutrients in our feces but we cannot consumed it again because there is other bad bacteria inside?

Post 48

@3rd post below: The epiglottis is a flap that prevents food from entering the lungs.

Post 45

@anon115923: I would like to know where you got your information from regarding the amount of time certain foods sit in the stomach.

Post 42

How does the stomach work?

Post 41

What does the epiglottis do?

Post 34

thank you. that really helped my homework out!

Post 32

In answer to the question; "How long does it take for food to digest?"

Fruit is not digested in the stomach, and so should be eaten alone to allow direct passage through the digestive system (if eaten with or after other foods, it will sit on top of it and spoil).

Vegetables remain in the stomach for about two or three hours before moving into the small intestine.

Starchy/carbohydrate foods (eg. rice, pasta, potatoes, etc.) remain in the stomach for about three hours

Animal proteins (eg. milk, cheese, meat) remain in the stomach for about four hours if no starch foods present (otherwise, will remain in the stomach for eight-plus hours).

High water content foods are the best kind for us humans. All other foods are concentrated. Only one concentrated food should ever be eaten at any one time in order to keep the digestive balance, use minimal energy for digestion and keep the stomach happy.

Post 31

this gave me everything i was looking for! Thank you.

Post 27

what do each of the organs in the body system do?

Post 26

wow. this is the best answer i've got.

Post 25

If you swallow a marble, can you die?

Post 24

how does the digestive system use energy? and how does it interrelate with the cardiovascular system and the respiratory system? Thanks

Post 21

I gained good basic information about the digestive system. thanks for that.

Post 19

I find the statement you made at the top paragraph of this website is ludicrous.

If it took hundreds of millions of years for our digestive system to develop, how on earth did we get the nutrients from the food during say the first million years? This is typical of the stupidity of the evolutionary theory. There is no such problem with the creation theory.

Post 16

I found all the answers I needed for my test.


Post 10

How long does the food digestion process take on average? Is it different for proteins, carbs, and fats?

Post 9

this website is very cool and i got all my information. thanks

Post 7

How long does it take for food to digest? -Em

Post 6

this a very interesting article about this type of human body that is needed to know for school which is good.

Post 4

I often hear it said that people have undigested red meat in their bowels. I've also read that "stuff" can build up on the walls of your colon. Is this true or is it an urban myth or made up by companies selling colon cleanse products?

Post 3

I would like to know how the digestive system helps the muscular system and how the digestive system also helps the skeletal system. Some reasons for the system are how they help other systems. So it would be cool if you could tell us how the digestive system helps the other 6 or 7 systems.

Post 1

How long does it take for food to digest?

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