Aorta

00:01 Let’s look at the aorta and the vena cava. They are very special blood vessels. Here is a section of the aorta. On the left-hand side, it’s sectioned and it has been stained with normal hematoxylin eosin. On the right-hand side, it’s a bit collapse but that happened during the processing. And the tunica media has been stained for elastic tissue. You can see then that the dominant fiber in the tunica media of the aorta is elastic tissue. It has a very, very important function. Here is a high magnification picture of this elastic tissue, and you can see the dark stained plates of elastic.

00:54 And if you look very very carefully in that elastic, you can see that there are fenestrae or small little gaps or pores between the elastic tissue, the sheaths of elastic which are branching.

01:08 That’s important because it’s important to understand that a blood vessel gets its nutrition directly from the lumen, or in some cases, very large vessels get their nutrition from vessels we call vasa vasora, vessels that come from the lumen or other vessels and they penetrate the tunica adventitia, and they run along the junction between the tunica media and the tunica adventitia, and they supply the wall of the blood vessels. So these fenestraes are important because it allows the diffusion of nutrients, oxygen, etc to go through the depths of the wall of the blood vessel. Blood vessels don’t have a direct blood supply or capillary bed going into them. Now, the role of this elastic in the aorta is very very important. When the heart pumps, when the ventricle contracts, the left ventricle contracts and passes blood up into the aorta, the aorta expands as it accepts that stroke volume of blood, a hundred mils or so. It expands because of the elasticity. That elastic tissue expands just like a rubber band stretching. And then when the heart goes through the resting or filling phase, when the ventricle has stopped contracting and is filling again as it resists blood coming from the left atrium, the elastic tissue inside the aorta then recoils just like an elastic band contracting back to its normal shape after you’ve stretched it.

02:53 And that recoil is very very important because what that does is it maintains pressure inside the aorta during the resting phase of the left ventricle. And because it maintains pressure during that resting phase or filling phase, it maintains the flow of blood.

03:14 And as you get older, that elastic tissue starts to disintegrate or be not so elastic, similar to the elastic tissue in the dermis of skin. When you look at the dermis of skin, you often see just very dense collagenous connective tissue. And that’s how the dermis is described. But it does have elastic tissue there as well. And like the aorta, the elastic tissue in your skin, degenerates with age as well. So your skin becomes wrinkling.

03:48 In the case of the aorta, when that elastic tissue loses a lot of its recoil ability, then it can create cardiovascular problems in the aged. So that’s the importance of that elastic tissue in the aorta.