Wikipedia:Osmosis/Aortic Dissection
Author: Kyle Slinn, RN, MEd
Editor: Rishi Desai, MD, MPH, Tanner Marshall, MS
An aortic dissection is where part of the tunica intima (which is the endothelial, or the innermost layer of a blood vessel) of the aorta is ripped off. What happens is a tear in the tunica intima of the aorta forms, and the high-pressured blood flowing through the aorta begins to tunnel between the tunica intima and the tunica media, separating the two layers. This is widely accepted as an unideal situation.
Now as the high-pressured blood continues to shear more and more of the tunica intima off the tunica media, blood starts to pool between the two layers, increasing the outside diameter of the blood vessel. The area where blood collects between the tunica intima and the media is called a false lumen, and the true lumen is the regular lumen of the blood vessel.
Since high pressure is a cause of aortic dissection, it’s no surprise that the aorta is the prime target for this problem. So what causes aortic dissections? Well, chronic hypertension is the major cause, whether the hypertension is caused by stress or from increased blood plasma volume like in pregnancy. Blood vessel coarctation, which is the narrowing of a blood vessel, also can cause dissection.
Aortic dissections most often happen in the first 10 cm of the the aorta closest to the heart. In order for an aortic dissection to occur, an underlying condition usually has to exist that weakens the aorta’s wall. Connective tissue disorders like Marfan’s and Ehlers-Danlos syndrome can cause a dissection, as well as a decreased blood flow to the vasa vasorum. Aneurysms can be a cause of aortic dissection as well, and incidentally dissection can also cause aneurysms because again, the dissection weakens the blood vessel wall.
In other words, weak walls can lead to outpouching of the blood vessel or a break in the tunica intima, and both of these weaken the walls further.
Aortic dissections cause a whole wack load of other problems too. A lot of complications are related to where the blood in the false lumen flows. The blood could flow back up the aorta to the heart and enter the heart’s pericardial space, filling it with blood and causing pericardial tamponade, a really really bad and potentially fatal situation. The blood flowing through the false lumen could also puncture a hole through the tunica media and tunica externa and bleed into the mediastinum, which would kill you really fast cause that’s a lot of blood leaving the vascular system quickly. The tunneling blood could also puncture a hole in the tunica intima and return into the true lumen which isn’t great but hey all things considered, it could be worse.
Yet another possibility is the blood could continue to tunnel between the tunica intima and the tunica media until it reaches another artery that branches off the aorta, like the renal arteries or the subclavian arteries. The blood in the false lumen can put pressure on these branching arteries decreasing blood flow to the kidneys and arms, causing a whole new mess to deal with.
And there you have it. That’s how aortic dissections happen!