What is the primary function of capillaries in the circulatory system?

The primary function of capillaries in the circulatory system is to facilitate the exchange of gases, nutrients, and wastes between the blood and the tissues. Capillaries are the smallest and most numerous blood vessels, forming extensive networks throughout the body's tissues. Their thin walls, composed of a single layer of endothelial cells, allow for efficient diffusion of oxygen and carbon dioxide, as well as the transport of nutrients like glucose and amino acids.

Additionally, capillaries enable the removal of metabolic waste products, such as urea and carbon dioxide, which are then transported away from the tissues to be processed and eliminated by the body. This vital exchange process occurs because capillaries connect arterioles (which carry oxygen-rich blood away from the heart) to venules (which carry oxygen-poor blood back to the heart), making them essential for maintaining cellular health and homeostasis throughout the body.