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Have a Heart!

heart-interior.jpgA friend recently brought up a question that had long nagged her: why are our hearts on the left side of our bodies instead of in the center? I thought I’d play Q&A columnist on this one.

While the human body on the outside appears symmetrical, internally it is not, and the primary reason seems to be space. The typical human torso exhibits left-right asymmetry because it can pack in only so much: for example, the heart, stomach, and spleen on the left, the appendix and gall bladder on the right. And actually, only about two-thirds of the heart is located left of the body’s midline. But we feel that side more strongly because our hearts’ left chambers pump blood to the rest of our bodies.*

Some people are born with their heart on the right. In others, all the organs are flipped—their bodies are basically mirror images of most people’s bodies, a condition called situs inversus. Symmetry can also occur. The heart can appear on the midline, in which case the person might have two left or two right lungs. These conditions aren’t life threatening unless "tubes and vessels don't connect properly," as this article puts it. The article states that about 35,000 birth defects every year are the result of organs growing in different places.

*The blood flow sequence is also responsible for the difference in size between the left and right lung. (That is, oxygen-poor blood enters the heart on the right and flows from there to the lungs, as you may all remember from biology class diagrams.)

Image from National Heart Lung and Blood Institute

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This page contains a single entry from the blog posted on December 27, 2006 9:30 AM.

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