Medical Gibberish: Anatomical Variants

The phrase anatomical variants refers to structures whose size, number, location, or pathway vary from the norm in a non-pathological way. Please make note of the “non-pathological” part of that last sentence. You almost assuredly have a few of these present within your own body and they won’t cause you problems. It could be a missing muscle in your forearm (14% of people are missing a muscle called the palmaris longus), aberrant vasculature to your gall bladder (30% of people differ from the norm in a variety of ways), or your thyroid gland could have decided to stay in your tongue instead of migrating down to your neck during development (not sure of the percentage, let’s say it’s rare). None of those examples are problematic. Lack of a palmaris longus means you’ve lost a potential source for a tendon graft but there’s no appreciable difference in grip strength or in effectiveness of sarcastic wanking motion. Gall bladder vasculature differences won’t matter unless your surgeon is in there digging around but he’s prepared for whatever you’ve got ready for him. A lingual thyroid gland can cause bleeding or difficulty swallowing but can also be unnoticeable…you might have your thyroid in your tongue right now. Anyway, now that I’ve said that these variations are no big deal I’ll bring up one that can most definitely cause you problems.

First, don’t let this get to you. There’s literally millions of ways your body can kill you at any second but evolution is amazing. You’re almost assuredly going to be fine for a nice long time. On to the background.

Your heart pumps blood to your body (you likely know this), but your heart also pumps blood to your heart. The muscular tissue of the heart (myocardium) needs an oxygenated blood supply just like tissue throughout the rest of your body. For a variety of reasons, the blood being pumped by your heart doesn’t fulfill this need simply by being within the heart (that’s not how gas exchange works, the right side of your heart only contains deoxygenated blood, etc). This need is filled by your coronary arteries which branch off immediately after blood leaves your heart (via the aorta) and than circle around while sending out various branches.

Anytime you hear of “coronary artery disease”, these are the arteries being referenced. Damage here is bad news. Not only is there not a lot of redundancy for cardiac blood delivery (redundant connections are called anastomoses and they save lives all the damn time by shunting blood to an area whose main delivery pathway is blocked), but there’s also no regeneration for damaged heart tissue. Once cardiac muscle cells are dead, they’re dead. You won’t replace that tissue with functional heart muscle over time.

Back to the variants. There are two main coronary arteries (left and right) and the structure of these arteries and their branches gives rise to left-dominant, right-dominant, and co-dominant hearts. This dominance doesn’t mean you have a stronger left or right side of the heart, but simply refers to whether a particular branch (posterior interventricular artery) is derived from the right or left coronary arteries. 70% of people are right-dominant, 20% are co-dominant, and 10% are left-dominant (if this is confusing see the picture below, it won’t help at all). All of these variants will give rise to a perfectly functional heart. The blood gets to where it needs to be and we’re none the wiser…until something goes wrong.

The tissue separating the right and left ventricles of your heart (the interventricular septum) receives blood predominantly from the left coronary artery, but the exact breakdown of blood source is determined by each heart’s specific organization of coronary artery branches. In right and co-dominant hearts, this septum receives blood from the left and right coronary arteries. If the left coronary artery is blocked, collateral circulation can develop via the also-contributing right coronary artery. In left-dominant hearts, this septum receives blood from only the left coronary artery. If the left coronary artery is blocked, there’s no chance of collateral flow developing and this blockage will cause a heart attack. So yeah, pretty fascinating. Enjoy your cheese fries.

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2 Responses to Medical Gibberish: Anatomical Variants

  1. Raysism says:

    My heart is the size of a Size 4 soccer ball, and stronger than a jackhammer. But my forearm is under my tongue and my penis is in my forearm.

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