Circulatory System For Kids - How does circulatory system work?

Your blood has lots of different jobs to do as it travels around your body. 
It carries the oxygen you have breathed in to every single cell.
It also carries food and other substances that your cells need.
When the cells have done their job, they make waste products which your blood carries away.

What is blood made of ?

Like other parts of your body, your blood is made from cells.
There are two main kinds of blood cells—red and white. 
The red blood cells are the ones that contain a red substance called hemoglobin. It is the hemoglobin in the red blood cells that carries oxygen from the lungs.
The white blood cells kill germs that enter your body. There are fewer white cells than red cells.
A liquid called plasma surrounds the blood cells. 
This is made mostly of water. The plasma carries food to the cells and carries waste products away.

Blood vessels - The tubes that carry blood

Blood travels through tubes called blood vessels. 
The vessels that carry oxygen-rich blood away from your heart are called arteries. 
The vessels that return the blood to your heart are called veins. 
There are thousands of arteries and veins all over your body. They branch into a network of very tiny, tubelike blood vessels called capillaries.
These are very thin so that they can carry blood to all the cells of your body.
Inside your veins are tiny flaps called valves. These open as blood is pushed through after each heartbeat, and they close again to stop the blood from running backwards.

Picking up food

As your blood flows through your body, it picks up food substances, called nutrients, that your cells need. Most of the nutrients enter your bloodstream from an organ below your stomach called the small intestine.
Your blood then carries the nutrients to your liver.
Your liver removes some of the nutrients from the blood and stores them until they are needed.
It also changes some of the nutrients into other substances that your body uses.
After your blood passes through your liver, it continues to carry these nutrients and other substances to all the cells.

Filtering the blood

Your blood is filtered when it passes through your kidneys. 
These lie behind your stomach, near your spine. They filter out some waste products and extra salts from your blood and make urine.
Each kidney passes urine through a tube, called a ureter, to your bladder. 
From the bladder, you excrete urine every day through the urethra.

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