Science Puzzle
Which Way Does the Blood Go?
Blood arrives back at your heart from your toes, having given up its oxygen. It must be refilled with oxygen at the lungs and pushed back out to the body again.
In what order does a single drop of blood make that journey?
The Answer
Body, right heart, lungs, left heart, body. Your blood passes through the heart twice on every circuit, which is why it is called a double circulation.
Oxygen-poor blood returns from the body into the right atrium, drops into the right ventricle, and is pumped a short distance to the lungs. There it dumps carbon dioxide and takes on oxygen. Now oxygen-rich, it returns to the left atrium, drops into the left ventricle, and is pumped out to every corner of the body.
The two sides never mix, and they are not equal. The left ventricle has to drive blood all the way to your toes and back, so its muscular wall is roughly three times thicker than the right ventricle's, which only has to reach the lungs next door.
The principle: Double circulation. Blood travels through the heart twice per circuit, once to reach the lungs and once to reach the body, keeping oxygen-rich and oxygen-poor blood separate.