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

最后，你的血管的最外层是外膜。

Next is the muscularis externa, a smooth muscle layer, which contracts automatically, without you even having to think about it.

往内是肌层，由平滑肌构成；它们不需要你的意志参与，便能够自主收缩。

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

外膜也有神经纤维、淋巴管，在最大的血管中也有弹性蛋白。

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，一些大血管拥有非常厚的外膜，以至需要有自己的血液供应。

Now, surrounded by the muscularis externa is the submucosa, which consists of a dense layer of tissue that contains blood vessels, lymphatics, and nerves.

在肌层包裹下的是粘膜下层；它由一层致密组织构成，其中含有血管、淋巴和神经。

And outside that, you have the muscularis externa layer, which as you might guess, is where you find the muscles responsible for moving food through your tube.

在那之外，你有肌层，正如你可能猜到的，是你发现负责通过管子移动食物的肌肉的地方。

To help churn the food, the stomach has an extra layer of oblique smooth muscle within its muscularis externa that allows it to contract and expand like a big accordion.

为了更好地搅拌食物，胃部的肌层还有一层额外的斜行肌，可以使胃部像一个大手风琴那样收缩和扩张。

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.

最后的外膜，由疏松结缔组织组成，含弹性纤维和胶原纤维，可保护和加固血管并使其固定。

Now, the esophagus has a particularly thick muscularis externa that propels the bolus of food down to the esophageal sphincter , which opens, allowing the bolus to pass into the stomach.

食管的肌层非常厚，这有助于食管将食团推向食管括约肌；食管括约肌适时开放，以便食团进入胃部。

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.

所以有些微小的血管，叫血管滋养管；拉丁语义为“血管的血管”：它们沿外膜走行，为血管壁提供营养。

But of course it's much more than just a storage tank — it's lined with the same four main layers found through most of the GI tract — the mucosa, submucosa, muscularis externa, and serosa — but it's got a few special modifications.

当然，它不仅仅是一个储存罐。它内衬着与大部分胃肠道相同的四个主要层——粘膜、粘膜下层、外肌层和浆膜——但它有一些特殊的修改。