Have you ever run so fast or climbed so many stairs that you could feel your heart beating in your chest?
The harder your body works, the more blood your heart needs to pump.
In this activity, you will learn how to:
The heart pumps blood, carrying nutrients and oxygen, through the arteries and veins.
The same pumping process also keeps blood moving to carry away carbon dioxide and waste.
Without the heart's pumping, the rest of the body cannot survive.
On Earth, gravity is pulling blood down, so the heart has to beat harder to push blood up towards the head.
In space, there is no gravity pulling blood down. The heart becomes deconditioned - it no longer has to pump blood as hard for blood to reach the head.
Heart rhythm and rate may also change. This is not necessarily a dangerous condition in space.
The heart must recondition itself to pump blood harder in order to overcome gravity.
Astronauts risk low blood pressure, dizziness and weakness during and after landing - a time at which they need to be in good shape to respond to any emergency.
NASA scientists are hard at work to help astronauts overcome the changes in the heart.
Part of understanding how the heart changes in space is understanding how the heart works on Earth.
The heart is mostly made of muscle, surrounding four chambers:
Each chamber helps push blood throughout the body.
The blood begins its journey through the arteries and smaller arterioles, delivering nutrients and oxygen to all the organs and tissue.
Along the way, it also picks up carbon dioxide and waste.
When the blood is completely deoxygenated (the red blood cells are no longer carrying oxygen), it flows to the heart.
Oxygen-poor blood first enters the heart through the superior and inferior vena cava, and flows into the right atrium.
The right atrium contracts and squeezes the blood into the right ventricle.
The right ventricle then contracts and forces the blood through the pulmonary artery to the lungs.
As the blood circulates through the lungs, red blood cells will collect oxygen and get rid of carbon dioxide.
Loaded with oxygen, the blood will flow through the pulmonary vein and into the left atrium.
The left atrium contracts, pumping the blood into the left ventricle.
The left ventricle then squeezes the blood through the aorta, the main artery of the body.
Then the cycle starts all over again!
Amazingly, it only takes 20 seconds for blood to completely circulate throughout the body.
The average heart beats 70 to 80 times per minute.
As we become more active, the heart beats faster.
You've learned a lot about how the blood flows through the major parts of the heart.