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# Structure and Function of Major Blood Vessels The human body has three main types of blood vessels: arteries, capillaries, and veins. Figure 3.8 illustrates the connections between them. Observe the direction of blood flow through arteries, capillaries, and veins in the figure. ## Table 3.1 St...

# Structure and Function of Major Blood Vessels The human body has three main types of blood vessels: arteries, capillaries, and veins. Figure 3.8 illustrates the connections between them. Observe the direction of blood flow through arteries, capillaries, and veins in the figure. ## Table 3.1 Structure and Function of Arteries, Capillaries, and Veins | Type of Blood Vessel | Structure | Function | Blood Circulation | |---|---|---|---| | **Arteries** | * Lumen (inner space): Thick walled, muscular, and elastic * Thick walls designed to withstand high pressure * No valves * Small lumen size | * Carry oxygenated blood away from the heart to the rest of the body (except the pulmonary artery). * Pulmonary artery carries oxygen-poor blood to the lungs. * High pressure blood circulation, quick flow * Pulse is detectable | | **Capillaries** | * Lumen (inner space): Single cell layer * Thin walls composed of a single layer of cells * No valves * Smallest lumen size.| * Facilitates gas, nutrient, and waste exchange between blood and body cells. * Gas, nutrient, and waste exchange between blood and body cells. * Easy diffusion of materials across thin walls|Slow blood flow, low pressure circulation | | **Veins** | * Lumens (inner space): Thin-walled, with some smooth muscle and elastic tissue * Valves to prevent backflow * Larger lumen size | * Carry deoxygenated blood back to the heart from the rest of the body (except the pulmonary vein). * Pulmonary vein carries oxygen-rich blood from the lungs. * Low pressure blood circulation, slow flow * Valves prevent backflow|