From the outside in, these are the adventitia, or serosa; the muscular layer; the submucosa and the mucosa.

从外到内看，分别是外膜（或者说浆膜）、肌层、黏膜下层与黏膜。

The outermost layer is either the adventitia, a thick fibrous connective tissue, or the serosa, a slippery serous membrane.

消化道的外膜，既有结缔组织构成的纤维膜，也有光滑、分泌浆液的浆膜。

In addition there is a thick muscular layer called the detrusor muscle that helps with bladder contraction during urination and it has fibrous adventitia outer layer.

此外，还有一层较厚的肌肉层，称为逼尿肌，能辅助排尿过程，其外层有纤维外膜。

Normally, the wall of the entire gastrointestinal tract is made of 4 layers: the inner mucosa, the submucosa, a muscular layer, and an outer layer called the adventitia.

正常情况下，整个胃肠道的壁由4层组成：粘膜层、粘膜下层、肌层和外层（即外膜）。