Patient Care Technician (PCT) AAH Practice Exam

Capillaries are referred to as microscopic blood vessels due to their extremely small diameter, typically measuring just a few micrometers wide. This small size allows them to facilitate the essential exchange of gases, nutrients, and waste products between the blood and surrounding tissues. Positioned between arteries, which carry blood away from the heart, and veins, which return blood to the heart, capillaries form a vast network throughout the body, ensuring that every cell has access to the blood's contents. In contrast, arteries and veins are larger blood vessels that play different roles in circulation. Arteries are responsible for transporting oxygen-rich blood away from the heart under high pressure, while veins carry oxygen-poor blood back to the heart, often aided by valves to prevent backflow. The aorta is the largest artery in the body, further highlighting how capillaries uniquely serve as the sites of exchange and interaction at the cellular level.