Which statement about the lamina propria is true?

The lamina propria is a critical component of the mucosal layer found in various organs, including the gastrointestinal tract and respiratory system. It is composed of connective tissue and is rich in blood vessels, lymphatics, and immune cells.

The statement that the lamina propria involves blood and nerve supply is accurate because it serves as a conduit for these essential systems. The blood vessels within the lamina propria provide nutrition and oxygen to the epithelial layer that overlays it, while also facilitating the transport of immune cells that play a vital role in the body's defense mechanisms. Nerve fibers found in this layer contribute to sensory functions and reflex actions.

Understanding the other options helps clarify why they are not correct. While the lamina propria does contain blood vessels, it is not the only layer with them; other layers of organs can have blood supply as well, especially in the broader context of organ pathology. Additionally, it does not have a significant amount of muscle tissue, as muscle is typically found in layers like the muscularis externa. Lastly, stating that the lamina propria is immune to tumor spread is misleading; the presence of immune cells does not provide immunity against tumor invasion, as tumors can indeed infiltrate the lamina propria.

Thus, the correct answer highlights