What are venules primarily composed of?

Venules are primarily composed of thin walls with smooth muscle, which allows them to serve their specific function within the circulatory system. These small blood vessels collect blood from the capillary networks and begin the process of returning it to the heart. The thin walls of venules are critical for facilitating the exchange of fluids and nutrients, as they are permeable and enable diapedesis, the movement of white blood cells into tissues.

Furthermore, the presence of smooth muscle in the walls of venules provides some degree of regulation over blood flow, allowing for constriction and dilation in response to bodily needs. This structural composition distinguishes venules from arteries, which have thicker muscular walls to withstand higher pressures, and capillaries, which are composed of a single layer of endothelial cells to optimize exchange.

The other options describe characteristics that do not align with the anatomical structure or physiological function of venules, as they either suggest attributes more suited to larger arteries or different tissue types altogether. Understanding the unique composition of venules is essential for comprehending their role in the venous system and the overall circulatory dynamics.