And finally, the outermost layer of your blood vessels is the tunica externa.

后，你的血的外层是外。

These arteries invest in additional smooth muscle tissue, and proportionally, have the thickest tunica media of any blood vessel.

这些动脉覆盖着额外的平滑肌组织，并按比例，拥有任何血厚的。

The tunica externa also has nerve fibers, lymphatic vessels, and in the biggest vessels, the protein elastin.

外也有神经纤维、淋巴，在大的血也有弹性蛋白。

Surrounding the tunica intima is the middle layer, the tunica media, made of smooth muscle cells and sheets of the protein elastin.

围绕内的是间层，，由平滑肌细胞蛋白质弹性蛋白片组成。

Both the cells of the tunica intima and tunica media generally get the nutrients they need from the blood in the lumen.

内的细胞，都能从腔内的血液获取所需的营养物质。

Next there's the tunica media or middle tunic which is mostly made of smooth muscle cells and sheets of elastin protein.

接下来是血，主要由平滑肌细胞弹性蛋白组成。

To make things really wild, some huge vessels have a tunica externa that's so thick that it needs its own blood supply.

神奇的是，一些大血拥有非常厚的外，以至需要有自己的血液供应。

The innermost tunic is called the tunica intima, which includes the endothelial cells, which create a slick surface that minimizes friction for blood moving through it.

内层者称为内，有内皮细胞构成；它们形成了光滑表面，使血液流经时的摩擦降到低。

The aorta also undergoes cystic medial necrosis, which is where there is degeneration of the tunica media, which is the central portion of the aortic wall.

除此之外，主动脉还会有囊性层坏死，即主动脉的发生退行性变；是主动脉壁的心部分。

Finally, there's the tunica externa or outside tunic which is made up of loosely woven fibers of collagen protein that protect and reinforce the blood vessel and anchor it in place.

后的外，由疏松结缔组织组成，含弹性纤维胶原纤维，可保护加固血并使其固定。

So there are tiny blood vessels, called the vasa vasorum, which means vessels of the vessels that creep along the tunica externa to bring nutrients to specifically that layer of the blood vessel wall.

所以有些微小的血，叫血滋养；拉丁语义为“血的血”：它们沿外走行，为血壁提供营养。

Anatomists call these layers " tunics, " and the innermost section is the tunica intima — which should be pretty easy to remember because, you know, it has like intimate contact with the lumen. It's like your circulatory underpants.

解剖学家称这些层为束腰外衣，里面的部分是内——这应该很容易记住，因为，你知道，它内腔有亲密的接触。就像你的循环内裤。