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Digestion - Eating and Elimination!

This is our favorite system. We love to eat and we love to poop. For the rest of the page we will refer to pooping as elimination. It's more technical that way. Anyway, your digestive system is all about getting food into your body, digesting the food, absorbing the nutrients you need, and elimination of the materials you don't need (feces). All animals have one sort of digestive system or another. Why? Anything that eats another creature (heterotrophs) must have a way of bringing nutrients in and getting rid of what they don't need.

What Does This System Do?

What does the system do? We're going to use you as the basis for our explanation of the digestive system. Let's start with eating. You get hungry and you eat. Once you put the food in your mouth, you start to chew and begin a process of mechanical digestion that grinds food down into a pulp.

Your body also starts to release enzymes that start the process of chemical digestion and the breakdown of biological molecules. Most chemical digestion happens in the stomach. The food moves through your digestive system and is eventually broken down into compounds and nutrients that your small intestine can absorb into the blood stream. The material you don't absorb continues into the large intestine where water is removed from the material and then whatever is left can be eliminated at your convenience. That's a decent overview of the process.

Interacting with Other Systems

The digestive system works very closely with the circulatory system to get the absorbed nutrients distributed through your body. The circulatory system also carries chemical signals from your endocrine system that control the speed of digestion.

The digestive system also works in parallel with your excretory system (kidneys and urination). While the digestive system collects and removes undigested solids, the excretory system filters compounds from the blood stream and collects them in urine. They are closely connected in controlling the amount of water in your body.


Nutrition is one of the most important ideas you can learn about. You can get hundreds of diseases if you don't have a balanced diet. An extreme example of malnutrition is called Kwashiorkor that occurs when you don't get enough protein in your diet. There are many disease related to missing individual vitamins and minerals including scurvy (vitamin C), beri beri (vitamin B1), or a goiter (iodine). The resulting goiter shows how the lack of one specific element can change the way your endocrine system works.

You probably learn about getting enough calcium in your diet. Your bones, tissues, and nervous system all need that calcium. Did you know that some people who don't have enough calcium (Ca) in their diets replace the calcium in their bones with magnesium? It can happen because calcium and magnesium are so similar on an atomic level.

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