The Excretory System

Contributor: Hannah Brooks. Lesson ID: 12385

What do you do with trash? Where does waste go when you flush the toilet? Without getting too gross, understand that your body has its own "sewer system." Learn the amazing way it functions! No sweat!


Earth Science

learning style
personality style
Grade Level
Intermediate (3-5), Middle School (6-8)
Lesson Type
Dig Deeper

Lesson Plan - Get It!

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Why do you think we filter our water before we drink it? Does it get filtered after we drink it?

We have to filter our drinking water so we are protected from germs and bacteria found in dirty water.

This keeps us healthy! Your body filters blood and waste in the same way that water filters work. Your kidneys are the organs responsible for removing waste from the body. They are an important part of the excretory system.

Before moving on, if you skipped or need a refresher on The Human Body lessons, find them in the right-hand sidebar under Related Lessons.

This body system helps you remove waste to maintain homeostasis. Homeostasis means that the body is staying balanced. Sweating is one way the body keeps balance, by cooling you off when you get hot. The excretory system is made up of the kidneys, bladder, liver, lungs, and sweat glands.

You have two kidneys located in the middle of your back, right below the rib cage. These two organs filter approximately 120 quarts of blood every day. To give you some perspective, a typical ice cream container holds about two quarts, so that's 60 ice cream containers! The waste collected from the blood becomes urine, around 1-2 quarts of urine each day! Blood reaches the kidneys through the renal artery, a large tube that connects the heart and the kidneys. Once the blood is in the kidneys, it is pushed towards special systems called nephrons. Each nephron is able to filter a small amount of blood. Notice how jumbled the nephron tubes are in the image below:

Once blood moves through the nephron, it becomes urine. Urine is then carried to the bladder through the ureter tubes. This pair of tubes connects the kidneys to the bladder. It can then be excreted from the body through urination.

The newly-filtered blood moves back to the heart through the renal vein, where it is pushed throughout the body.

So, what do the lungs and sweat glands do in this system? Well, lungs help remove carbon dioxide gas from blood and tissues and release it as waste. Release a large breath. You just released a high amount of carbon dioxide waste. Notice how the lungs work with the circulatory system to ensure a healthy balance of gases.

Another organ that helps filter out waste is the liver. This organ detoxes, or cleans out, any chemicals in the body, like any medications you may have taken. It also produces bile, a substance that helps break down fats and waste for removal. Finally, your sweat glands remove salts and other compounds from your body when you become overheated.

All of these body processes help keep waste and toxins moving out of your body.

  • What do you think would happen if one of these organs stopped working?
  • How are the kidneys and liver similar?

The filtering of blood is constantly occurring, providing your tissues and cells with clean blood that is able to carry oxygen and nutrients. Your liver is using bile to break down the fats brought into your body through the food you eat.

Reflect on the role of each organ by summarizing the information on a sheet of paper.

In the Got It? section, you will review the major parts of the excretory system in an interactive.

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