In the layers of the bladder wall are a mucosa layer that has a transitional epithelium, which is stretchy and allows the bladder to distend while maintaining a barrier between urine and the body.

膀胱壁多层结构中的粘膜层为变移上皮，变移上皮富有弹性，使膀胱扩张的同时，保证尿液不进入组织液。

The bladder is able to expand and contract because it's wrapped in a muscular layer, called the detrusor muscle, and within that, lining the bladder itself is a layer of transitional epithelium containing " umbrella cells" .

膀胱既可以扩张也可以收缩，因为膀胱壁有一层肌肉，叫做逼尿肌，而且膀胱内衬有一层由“伞状细胞”（盖细胞）组成的变移上皮。