4*Also called“Tunica adventia”Tunic/VesselTunica IntimaTunica mediaTunica externa*ArteryXVeinCapillaryOnly tunica intima in capillaries
5CapillariesWalls of capillaries are only one cell layer thick to allow for exchanges between blood and tissueOnly capillaries directly serve the needsof the body’s cells. It is through the capillaryWalls that exchanges are made between tissue cells and blood.Respiratory gases, nutrients, and wastes move along diffusion gradients.
8Elastic recoil of artery propels blood along They have the greatest amount of elastin, enabling them to expand. When the heart relaxes, the recoil propels blood onward.
9Muscular Pumps aids blood flow in Veins As skeletal muscles surrounding the veins contract and relax, blood is milked through the veins toward the heart.
10Respiratory Pump aids blood flow in veins! Pressure changes that occur in the thorax during breathing also aid blood return to the heart through the veins.
11Arteries are thicker than veins Because arteries are closer to the pumping action of the heart, they must be able to expand as blood is propelled into them and then recoil passively as the blood flows off into the circulation during diastole. Arterial walls must be strong and resilient to withstand blood pressure fluctuations.