Valentine's Day Special: How Does the Heart Work?
When I was teaching middle school, I would always start the unit on the Circulatory System by asking students to squeeze their hand in a fist about once every second for as long as they could. Go ahead, give it a try. How long can you last? 30 seconds? A minute or two? Your heart does this every second of every minute of every hour for (hopefully) many, many years. It’s an impressive organ that has some pretty cool mechanisms to make it work.
First, the structure. The heart is a muscle. A big, strong muscle. Well, it’s actually not that big; it’s about the size of both of your fists combined.
The heart has four chambers, which you’ve probably heard before. Two chambers are smaller and collect blood. These are called atria (one is an atrium). The other chambers are bigger and pump blood elsewhere. These are called ventricles.
Take a look at the simplified drawing below. Blood comes from the body into the right atrium. It then passes into the right ventricle, which pumps it to the lungs to get more oxygen (and get rid of carbon dioxide). The oxygenated blood reenters the heart at the left atrium and goes into the left ventricle. Finally, the left ventricle pumps it to the rest of the body.
The diagram looks like it has left and right switched. It’s because you’re looking at a heart as it would be in someone else standing across from you. I also didn’t draw the oxygenated blood as red and deoxygenated blood as purple because it’s not. Blood is red. The textbook drawings with red and blue blood are misleading and I don’t like them. Just remember that the right side (of the heart, not the diagram) is deoxygenated because it’s going to the lungs, and the left side is oxygenated because it’s going to the rest of the body.
The right side takes deoxygenated blood from the body and sends it to the lungs for more oxygen. The left side takes this freshly oxygenated blood and pumps it to the rest of the body. (oxygenated = full of oxygen; deoxygenated = not full of oxygen)
The heart also has a cool system of valves that (usually) prevents blood from flowing in the wrong direction and a highly specific electrical system to control all of the muscle movement, but those are discussions for a different day.
As for why a heart is represented by a “heart shape” (<3), scholars are in disagreement. In 5th-6th Century BCE, a plant with a heart-shaped leaf may have been used for birth control, so the symbol may have come from there. There also may be connections between the heart shape and the shape of flowers, fruits, and seeds, which all have to do with reproduction. The earliest recorded use of the heart shape to represent romantic love was in the 1200s in a French manuscript. The Wikipedia article is fascinating - you should check it out.
Either way, the actual heart is, unfortunately, not exactly heart-shaped. I think everyone should be buying Valentine’s Day cards with anatomically correct hearts on them. Happy Valentine’s Day!
Sources: https://www.uofmhealth.org/health-library/tx4097abc