The Circulatory System

Contributor: Hannah Brooks. Lesson ID: 12379

You have probably cut yourself or had a nosebleed. How did the blood get to that area? How and why does it get anywhere? Learn about this organ that pumps blood and keeps you alive without your help!


Life 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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  • How does all that water fit inside your little faucet?

You know it has to come through pipes throughout your house!

  • How does blood get to all the parts of your body?

The water in your house runs through pipes from a central location to each faucet.

It follows a pathway, much like blood in your body.

Before continuing, if you missed or need a refresher on the previous lesson in The Human Body, find it under Related Lessons in the right-hand sidebar.

The circulatory system is responsible for moving blood through your entire body, from the skin on your scalp all the way down through your legs to your toes.

The circulatory system is made up of your heart and blood vessels. Blood vessels are small tubes called arteries, veins, and capillaries. Each of these body parts has a specific job in the circulatory system.

circulatory system

The circulatory system depends on the heart, an organ, to pump blood throughout the body.

Blood is a fluid made up of cells. There are red and white blood cells in your blood that keep you healthy and move oxygen throughout your body.

The heart is an involuntary muscle, meaning it beats without direct instruction, or conscious thought, from the brain.

  • What do you think would happen if your brain had to tell your heart to pump?
  • If you had to think about every heartbeat?
  • Do you think you would forget?
  • What do you think would happen while you slept?

Most people's heart beats between 60 and 100 times per minute.

  • What do you think causes the heartbeat sound?

It is small valves in the heart closing and opening! The heart is located between the lungs in the chest cavity.


Your heart is made up of really thick muscles that are very strong. The muscles beat together, which is why the heart is able to pump so much blood! The heart has four parts, or chambers.

heart chambers

The heart is divided top from bottom. The top is called the atria. There is a left atrium and a right atrium. The atria take blood from the body and move it into the heart.

The bottom of the heart is called the ventricle. There is a left and right ventricle, which pump blood out of the heart. This helps our body circulate blood throughout the day.

The wall between the left and right parts of the heart is called the septum. It keeps blood from mixing in the heart.

  • Did you know that the largest blood vessel in your body is over a foot long?

It is called the aorta, and is located on the top of the heart. It pumps blood carrying oxygen away from the heart. It is located at the very top of the red section in the diagram above.

  • Why do you think oxygen is an important part of blood?

Your organs and tissues need oxygen in order to function! This blood provides cells in your body with the oxygen needed to live.

blood cells

Arteries and veins are also blood vessels. Arteries have really thick walls, and branch into smaller arteriole tubes as the reach farther away from the heart.

artery wall

Veins move de-oxygenated blood back to the heart. De-oxygenated means that the blood has already given the oxygen to organs and tissues throughout the body.

This occurs through a series of valves that prevent blood from flowing backwards. These valves work the same way as stoplights, keeping blood moving in the right direction.

vein valves

Veins are less flexible and have a thinner muscle layer than arteries. The superior vena cava and inferior vena cava are the largest veins, and are located above and below the heart.

Veins and arteries are connected by capillaries, the smallest type of blood vessel. These tiny structures allow veins and arteries to exchange water, carbon dioxide, nutrients, and a small amount of oxygen. They are also responsible for delivering oxygen and nutrients to cells and for removing waste products from cells.

Your circulatory system depends on another set of organs, the kidneys, to remove the waste collected in the blood from the body.


All these components work together to move blood throughout the human body.

The heart pumps large amounts of blood out to arms and legs, providing necessary oxygen to these areas. Arteries move blood away from the heart, while veins take blood back to the heart, where it goes through a sort of recycling process and is oxygenated once again. Capillaries are important structures for providing oxygen and nutrients to cells and provide arteries and veins a way to exchange blood.

Your heart is an amazing muscle, providing the nutrients and blood supply for your entire body. Arteries, veins, and capillaries act as pathways, moving the valuable fluid to tissues and organs.

  • Have you ever felt your pulse increase in your wrist or neck?
  • Why do you think your heart beats faster when you are excited or scared?
  • How can you help control the pace of your heart beat?

Run in place for two minutes.

  • What happened to your heart beat?
  • Why do you think that occurred?
  • How does the circulatory sytem control your heartbeat in a stressful situation?

In the Got It? section, complete a guide to help you learn more about the structure of the heart and the way it pumps blood!

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