Although the main structure and function of veins is almost similar to that of arteries but there are some very minute differences between the two. Some functional difference which exist between the vain and arteries are as follows:
Veins usually transport blood at a lower pressure as compared to arteries. This is because these are not as strong as arteries. The structural analysis of veins and arteries and their comparison shows that the connective and muscle tissues are thicker in arteries as compared to those in veins. Therefore arteries can bear more pressure of blood as compared to veins.
A structural analysis of veins shows that like arteries, veins are also composed of three layers. The outer layer of a vein cross section shows the presence of a connective tissue. Inner to this connective tissue layer lays the muscle layer. The innermost layer is composed of thin endothelial tissue. The major difference between the layers of arteries and veins is that these layers found in veins are quite thin as compared to those in the arteries. The presence of less tissues results in less endurance of pressure by veins. Another property of veins is that as depicted by the structure of veins, there is a larger space inside the veins. Due to this increased diameter of lumen in veins, these are capable of carrying more blood at a time.
The reason behind thin veins is that these are composed of thin layers of connective and muscle tissue. The way in which the veins transport blood from one part of body to another part is very simple. After the blood reaches the cells, its oxygen content is exchanged for carbon dioxide. Now the blood is called as the deoxygenated blood. After the exchange of gases the blood is transferred from capillaries to veins. This blood is carried from veins to heart. As the veins cannot endure much pressure of blood therefore these are located at the surface of body near skin. As the veins contain deoxygenated blood, which is why they appear as purple streaks on skin.
Another additional property of veins which is not present in arteries is the presence of valves. As the veins have to transport deoxygenated blood in a specific direction, a specific mechanism should be devised to prevent its backflow. This backflow of blood in veins is prevented by means of valves that are found in the inner diameter smoking and high blood pressure or lumen of veins. Therefore the valves facilitate the blood to flow in one direction only even if it is against the gravity.
The valves also play an important role specifically when the blood needs to be transported to brain. Transporting of blood to brain also requires energy as this task is being done against the gravity. Therefore the strength of valves present in veins is very important to keep the blood flow in right direction. The blood flowing through veins is deoxygenated. That is why it is not red in color. In fact it is deep red or maroon in color.