Why do we have blood? Where does it come from? –Norelle, Olympia, Wash.

Dear Norelle,

Our bodies have many living parts, like skin, muscle, brain and bones. Blood helps keep these parts alive and healthy. The system that moves our blood around the body is sort of like a city’s postal service, said my friend Astrid Suchy-Dicey.

Suchy-Dicey is a scientist at Washington State University who is really curious about blood. Her research helps people at risk for diseases.

She said it first helps to know that blood is actually made up of different things: red blood cells, white blood cells, platelets, and plasma.

If you think of your circulatory system like the postal service, mail carriers are the red blood cells. They transport important packages and letters (oxygen) over a vast network of streets and highways (blood vessels).

About a gallon and a half of blood circulates through the human body, dropping off these deliveries, 24 hours a day. The strong heart muscle pumps blood out into the body. It’s working hard, too. The force needed to squeeze a tennis ball is similar to what you need to squeeze blood out of the heart.

White blood cells help your body fight off infections. There are lots of different types of white blood cells with different jobs. Some of them fight off tiny bacteria and fungi. Some of them fight off viruses or other invaders.

All of the white blood cells’ jobs have one common mission: keeping you healthy.

Platelets help keep you healthy, too. Whenever you get a cut or scrape, these disc-shaped parts come to the rescue. Platelets help stop blood from flowing. They also help prevent you from losing blood and keep out invaders.

Plasma is a watery solution with a few other things floating in it, like salt and proteins. It flows, carrying other cells freely along those streets and highways we know as blood vessels.

As for your second question, Suchy-Dicey said that blood cells are produced in your bones. Specifically, they are produced in the soft fatty part inside your bones called bone marrow.

Your plasma is formed mostly using water you drink. That’s why it’s really important to drink enough water each day, Suchy-Dicey adds. While on the issue of water, here’s a quick activity you can try to find out about how much blood your heart pumps in a minute.

You’ll need a bucket of water, an empty bucket, and a small Dixie cup. Fill a bucket with about a gallon of water. Have a friend set a timer for one minute and see how many little cups of water you can move to the empty bucket.

Each time your heart beats it moves about a small Dixie cup’s worth of blood. It takes our heart about one minute to pump about a gallon of blood. Can you move the liquid faster than a heart? Try it out sometime and let me know how it works.

Sincerely,
Dr. Universe