Basics of the Excretory System

Contributor: Hannah Brooks. Lesson ID: 12572

You know you eat tasty food that eventually comes out as . . . well, something else. Just like you throw out trash, your body disposes of waste. Learn all about your body's built-in filter system!


Life Science

learning style
personality style
Grade Level
Middle School (6-8), High School (9-12)
Lesson Type
Dig Deeper

Lesson Plan - Get It!


How does a coffee filter work? Is there one in your body?

Coffee filters hold the coffee grounds while water moves through and collects the flavor from the grounds.

The filter holds the grounds as waste, easily removed and thrown away. Filters like coffee filters work just like your kidneys. Your kidneys are organs responsible for removing waste from the body. They are an important part of the excretory system.

excretory system

This body system helps you remove waste and maintain homeostasis, or a balanced internal environment. It is comprised 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 structures filter at least 120 quarts of blood every day! The waste becomes urine, around 1-2 quarts! Blood reaches the kidney through the renal artery, which directs blood to nephrons, special cells that filter a small amount of blood. These complex cells have different components working to separate blood from waste. You will learn more about the structures pictured below as you complete the lesson:


Once blood moves through the nephron filtration process, it becomes urine. Urine is then carried to the bladder via the ureter tubes. 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 redistributed through the body.

So, how do the lungs and sweat glands contribute to 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 concentration 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 any chemicals in the body, like medications and alcoholic beverages, which can take hours for the body to process. It also produces bile, which helps break down fats and waste for removal.

Finally, your sweat glands contribute by removing salts and other compounds from your body when you get hot.

All of these body processes function to keep waste and toxins moving out of your body, even though they are not directly linked.

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

The blood filtration process is constantly occurring, providing your tissues and cells with clean blood able to carry oxygen and nutrients. Your liver is using bile to break down the fats found in your breakfast or lunch.

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

In the Got It? section, you will learn more about the structure of nephron cells working to filter blood.

Elephango's Philosophy

We help prepare learners for a future that cannot yet be defined. They must be ready for change, willing to learn and able to think critically. Elephango is designed to create lifelong learners who are ready for that rapidly changing future.