1. Circulatory System

2. The Circulatory System
The circulatory, or cardiovascular, system is made up of the heart, blood vessels, and blood.
In one day, human hearts beat about 100,000 times and pump around 1,500 gallons of blood!
Whew! I’m tired!

3. What does it do for us? Our circulatory system…
Delivers necessary materials (like oxygen and sugar) to the entire body in the blood,
Removes waste products from cells, and
Helps fight disease by transporting immune cells in the blood.

4. How does it move stuff?
The circulatory system is like a system of roads that links your entire body
The “roads” are blood vessels – some are like superhighways, and others are like small one-lane paths.
Your blood travels on these roads like a “mail man” – it both delivers and picks up important materials.

5. How does it move stuff? Your blood travels in two main loops:
From the heart to the lungs and back, and
From the heart to the body and back.

6. How does it move stuff? Basically, your blood follows this cycle:
Blood gets rid of carbon dioxide and picks up oxygen.
Blood enters the right side of the heart and is pumped out again.
Blood enters the left side of the heart and is pumped out again.
Blood delivers oxygen to body and picks up waste (like carbon dioxide).

7. Oxygen-poor blood from the body enters the right side of the heart and is pumped out to the lungs.
Oxygen-rich blood from the lungs enters the left side of the heart and is pumped out to the body.

8. How does it move stuff?
Your heart is the pump that sends the blood through the system.
The heart is a hollow, muscular organ.
RIGHT ATRIUM
LEFT ATRIUM
LEFT VENTRICLE
RIGHT VENTRICLE
Inside the heart, there are four main chambers: two atria (right and left) and two ventricles (right and left).

9. What’s inside your heart?
SEPTUM
The right and left sides of the heart are separated by a wall of tissue called the septum.

10. What’s inside your heart?
VALVE
VALVE
The atria receive the incoming blood, and the ventricles pump it back out, either to the lungs or to the body.
The atria and ventricles are separated by valves, which prevent blood from flowing in the wrong direction.

11. So, the detailed path of blood in your body would look like this:
From Body
Right Atrium
Right Ventricle
To Lungs
From Lung
Left Atrium
Left Ventricle
To Body
Lung
Body

12. What’s inside your heart?
The ventricles are in charge of pumping the blood out to the entire body. They need to be thick and strong to have enough force!
This is a real sheep heart. Look at how thick the walls of the ventricles are. Why is this?

13. Heart Facts
Hold out your hand and make a fist. If you're a kid, your heart is about the same size as your fist, and if you're an adult, it's about the same size as two fists.
Your heart beats about 100,000 times in one day and about 35 million times in a year. During an average lifetime, the human heart will beat more than 2.5 billion times.
Give a tennis ball a good, hard squeeze. You're using about the same amount of force your heart uses to pump blood out to the body. Even at rest, the muscles of the heart work hard--twice as hard as the leg muscles of a person sprinting.

14. What carries the blood?
BLOOD VESSELS are the hollow tubes that carry your blood around your body.
There are 3 TYPES:
ARTERIES
CAPILLARIES
VEINS

15. What carries the blood? Arteries carry blood away from the heart.
They are very thick, and have strong, muscular walls to withstand the pressure created by the heart.

16. What carries the blood?
Capillaries are tiny vessels that run through your body tissue.
They are very thin to allow oxygen and waste to pass between the vessels and your cells.

17. What carries the blood? Veins carry blood back to the heart.
They have thinner walls than the arteries because there is not as much pressure from the heart.

18. This vast system of blood vessels - arteries, veins, and capillaries - is over 60,000 miles long. That's long enough to go around the world more than twice!

19. What is your blood?
Blood is not one single substance – it is a mix of liquid and cells.
The liquid part of blood is called plasma. It is mostly water.
The rest of the blood is made of three types of cells.

20. Is Blood Blue?
Your veins are not actually blue. They are a dark reddish-brown, but appear blue because the fat under our skin only allows blue light to travel all the way down to our veins. Since it is the only color of light that makes it to our veins, it is the only color that is reflected, and thus our veins appear blue! I hope this helps
Everyone's skin is slightly different in color, so the veins can look different in different people, but blood is exactly the same color in everyone. It still doesn't look red. That's because we're seeing the *walls* of the veins too.

21. What is your blood? Red Blood Cells carry oxygen.
White blood cells fight disease.
Platelets form blood clots to stop you from bleeding too much.