Capillaries are the smallest blood vessels in the circulatory system, essential for the exchange of gases, nutrients, and waste products between blood and tissues. Their thin, semi-permeable walls enable efficient diffusion of oxygen and carbon dioxide, facilitating cellular respiration. Capillaries connect arterioles and venules, creating a vast network that ensures even the most remote cells receive adequate supplies and eliminate waste. This intricate system plays a crucial role in maintaining homeostasis by regulating blood flow and pressure, as well as supporting vital physiological functions throughout the organism.