Veins

Veins are similar to arteries, but since they transport blood at a lower pressure, they are not as strong as arteries. Like the arteries, veins have three layers: an outer tissue layer, thews in the middle, and a smooth inner epithelial cells layer. However, the layers are thinner and containing less tissue.

Veins receive blood from the capillaries after an oxygen and carbon dioxide exchange has taken place. Thus, the veins transport blood back to the lungs and heart. It is important that the waste-rich blood moving in the correct direction and not be allowed to flow back. This is achieved by valves, which are located inside the veins. Valves are like gates, which only allow traffic to move in one direction.

The vein valves are necessary to maintain blood flowing toward the heart, but they are also necessary to allow blood to flow against gravity. For instance, blood that returns to the heart from the foot should be able to flow up the legs. Typically, the force of gravity would discomfort that. Valves of veins, however, provide a springboard for blood as it climbs the way up.

The blood that flows to the brain faces the same problem. If blood had difficulty getting up, you feel dizzy and perhaps even faint. Syncope of course, ask your brain to more oxygen-rich blood. When you faint, your head comes to the same level as your heart, making it easy for the blood rapidly reaches the brain.

Because lack of oxygen, the waste-rich blood that flows through the veins has a deep red color, almost like maroon. From the walls of veins rather thin, the waste rich blood is visible through the skin on some parts of the body. Look at your hands or ankles. You will probably see your veins carrying your blood to your heart. Your skin will refract the light, so that deep red color actually see a little blue from the outside skin.