Final answer:
The true statement is that the muscularis mucosa consists of involuntary smooth muscle fibers. The mucous membrane includes the epithelium, lamina propria, and the muscularis mucosae layer, which plays a crucial role in the functionality of body cavities exposed to the external environment. The correct option is D.
Step-by-step explanation:
The mucosa, often referred to as a mucous membrane, is a unique layer that lines various cavities in the body and is exposed to the exterior environment. It plays a significant role in functions such as digestion, respiratory, and excretory processes.
The mucous membrane consists of a few different layers, with the epithelium being the layer in direct contact with the ingested substance or air. Beneath this lies the lamina propria, a supportive layer of connective tissue. Additionally, the mucosa includes the muscularis mucosae, a thin layer of smooth muscle fibers which is involuntary.
Addressing the options provided in the question, the correct statement is letter d: 'The muscularis mucosa consists of involuntary smooth muscle fibers.' Option a is partially correct but incomplete since the mucous membrane is composed of multiple layers that include more than just the epithelium and the lamina propria.
Option c is incorrect as the lamina propria supports the mucous membrane, not the skin. Finally, option e is incorrect; while it is true that the peritoneal cavity separates the visceral and parietal layers, the cavity contains peritoneal fluid, not mucous liquid.