Your Heart's Four Chambers: How Blood Makes Its Loop

Right now, your heart is beating about 70 to 100 times a minute. That adds up to roughly 100,000 beats a day, moving about 2,000 gallons of blood, enough to fill a small backyard pool. It never takes a break, not even while you sleep. But your heart is not just one open bag of blood. It is split into four separate rooms, called chambers, arranged so that clean and dirty blood never mix. Understanding those four rooms is the key to understanding how oxygen reaches every cell in your body.

By the end of this lesson you will be able to: - Name the four chambers of the heart and say what each one does - Trace the two loops blood takes: one to the lungs, one to the body - Explain how heart valves force blood to move in only one direction - Read a simple diagram of blood flow and predict what happens if a valve leaks

The heart has a top pair and a bottom pair of chambers. The two top chambers are called atria (one is an atrium). They are the receiving rooms: blood flows INTO them. The two bottom chambers are the ventricles. They are the pumping rooms: their thick muscle walls squeeze blood OUT. A wall called the septum runs down the middle, keeping the right side and the left side completely separate. The right side handles oxygen-poor blood coming back from your body. The left side handles oxygen-rich blood coming back from your lungs. Because the left ventricle has to push blood all the way to your toes and back, its muscle wall is about three times thicker than the right ventricle's.

Blood actually makes two connected loops every time around, and your heart runs both at once. The pulmonary loop is the short trip to the lungs. Oxygen-poor blood enters the right atrium from two big veins (the vena cavae), drops into the right ventricle, and gets pumped through the pulmonary artery to the lungs. There it drops off carbon dioxide and picks up fresh oxygen. The systemic loop is the long trip to the body. The now oxygen-rich blood returns to the left atrium, drops into the left ventricle, and gets blasted out through the aorta, the body's largest artery, to reach your brain, muscles, and organs before returning oxygen-poor to start again.

Between and out of each chamber sits a valve, a flap that opens one way and slams shut to stop backflow. There are four: the tricuspid (between right atrium and right ventricle), the pulmonary valve (to the lungs), the mitral valve (between left atrium and left ventricle), and the aortic valve (to the body). That 'lub-dub' sound a doctor hears through a stethoscope is the valves snapping shut. 'Lub' is the mitral and tricuspid closing as the ventricles squeeze; 'dub' is the pulmonary and aortic closing as the ventricles relax. If a valve leaks, blood sloshes backward and the heart has to work harder, which a doctor may hear as an extra whooshing sound called a murmur.