Final answer:
The three layers of smooth muscle in the bladder's muscularis are collectively known as the detrusor muscle. This muscle's function is crucial for the expulsion of urine. The bladder is lined with transitional epithelium apt for volume changes and covered by the peritoneum.
Step-by-step explanation:
The muscularis of the bladder consists of three layers of the smooth muscle collectively called the detrusor muscle. The detrusor muscle is responsible for the contraction of the bladder to expel urine. It is made up of irregular crisscrossing bands of smooth muscle fibers that run in all directions to reduce the size of the organ when emptying it of urine. The detrusor is part of the muscularis layer of the bladder, which helps move urine toward the bladder through peristaltic contractions.
The bladder is lined with transitional epithelium, which can handle stretching as the bladder fills with urine. Distensible nature of the bladder is due to this unique epithelial lining which resembles columnar epithelia when empty and transitions to squamous appearance when stretched. The innermost layer, the mucosa, is supported by a submucosal layer that attaches to the muscular detrusor layer. The outermost covering of the bladder is the peritoneum, which is part of the abdominal cavity lining.