Based on the provided reference, the answer is: There are not three layers of serosa, instead, the serosa is the outer layer covering other layers.
Let's break down the layers of a structure based on the provided text:
| Layer | Description |
|---|---|
| Mucosa | The innermost lining, also known as the mucous membrane. |
| Submucosa | The middle layer, located beneath the mucosa. |
| Muscularis externa | The outer layer, responsible for muscular functions. |
| Serosa | The outermost layer that covers and protects the muscularis externa. |
Therefore, based on the text provided, the serosa is a single, outer layer not composed of three distinct layers. Instead, it's the outermost of the four layers described.
