Heart and Blood

Blood by the Numbers Amount of blood: 7 to 8 liters Number of red blood cells: 25 trillion Forty percent of blood (by volume) is red cells Number of platelets: 2 trillion Number of white blood cells: 40 billion

You already know that, as it’s beating inside your chest, your heart pumps blood sending it all over your body. But why is that? Your heart has two sides. Each side acts like two different pumps. The first pump sends blood to the lungs. In the lungs, two things happen. Your red blood cells attach to oxygen in the lungs. They also release carbon dioxide molecules that they have carried from your body’s cells. This is why you breathe in air that contains a lot of oxygen, but breathe out air that contains a lot of carbon dioxide.

Next, your blood goes back to the heart, and the second pump shoots it out to your body. Along the way, many different things happen. Probably the most important thing is that the red blood cells release their oxygen to your body’s cells and then they pick up carbon dioxide released by the cells. Miles and miles of tiny blood vessels called capillaries take the blood close to every cell in your body.

The blood passes near the small intestines, and if you have eaten recently, the blood picks up all sorts of food molecules. Fat molecules, sugar molecules, protein molecules, vitamin molecules, mineral molecules and water molecules leak through the wall of the small intestine into the blood. The blood then carries these molecules all over your body to every cell that needs them.

What if you haven’t eaten recently? Along the way, your blood flows through your liver, and the liver does two things. It helps convert toxins out of the blood. Your liver also stores and releases glucose. You liver is like a big sugar storage tank. For example, when you wake up after sleeping for 10 hours and your muscles need glucose to get moving, they get it from the liver. Your blood also goes through your kidneys. Your kidneys take out excess water, along with ammonia and many toxins and send it all to your bladder in urine.

Sealing a Leak When you get a cut, platelets that are floating in the blood help plug the leak. The platelets can sense oxygen in the air. They break up and start forming very thin threads, like a net. The net catches red blood cells, which harden to form a scab.

Your blood passes many organs that either create or use hormones. Hormones are chemicals that let different parts of your body send signals to other parts. Adrenaline is one hormone that you may have heard of. You have two glands called the adrenal glands that sit on top of your kidneys. They can squirt adrenaline into the blood. The adrenaline tells your heart to beat faster, your pupils to constrict, your blood vessels to stop sending blood to the stomach and the skin, and your liver to make more glucose available in the blood.

As you can see, every molecule that moves in your body uses the transportation system called blood. And your heart keeps the blood moving. Without blood, the cells in your body would not have any oxygen. They would not have any glucose. There would be too much carbon dioxide, and there would be toxins everywhere. Blood is really important.