What are the walls of capillaries primarily composed of?

The walls of capillaries are primarily composed of endothelium, which is a type of simple squamous epithelium. This specialized tissue layer provides several essential functions in the circulatory system. Its thin structure allows for efficient diffusion and exchange of gases, nutrients, and waste products between the blood and surrounding tissues.

Endothelial cells are tightly packed, creating a barrier that regulates the passage of substances, crucial for maintaining homeostasis. Additionally, the simplicity of the endothelial layer minimizes the distance materials must travel, facilitating faster and more effective exchanges than would be possible with thicker walls made of muscle fibers or connective tissue.

While other tissue types, such as muscle and connective tissue, play important roles in the function of larger blood vessels, the unique composition of capillary walls is specifically adapted for their primary role in nutrient and gas exchange.