The human body is an ideal example of the perfect harmony between structure and function; every part serves a purpose.
Arteries and veins differ in many ways, including diameter, strength, durability, and valves. Arteries have thick walls that can withstand high pressure. When the heart pumps blood, there is high pressure in the arteries, which we call blood pressure. High blood pressure is necessary for the heart to pump the blood to parts of the body, especially to the brain. In fact, in order to send enough blood to the brain, the sympathetic nerves press against the muscles around the walls of the arteries, by which the pressure is raised further and blood carried to every part of the body. The walls of arteries are thus created thick and strong so that they can resist such high pressure. When the system breaks down and the pressure is higher than necessary, the arteries may tear, resulting in bleeding in the brain, paralysis, or even death.
The walls of the veins, in contrast, are created thin. The arteries are vessels that feed us, while the veins shuttle used blood back to the heart. The arteries do not expand much, nor do they store much blood. No more than 15% of the blood in the body is found in the arteries.
The veins can expand due to their thin walls and store more blood. A total of 65% of the blood is found in the veins. While the arteries are equipped with features to function with little blood and high pressure, the veins are built to hold more blood, but at a lower pressure. The veins function as a blood tank that is tapped immediately in times of bleeding, especially to delay the death of the brain. In case of bleeding when the brain cannot get oxygen, the body declares a state of emergency. The sympathetic nerves convey messages to the arteries and veins. The muscles in the arteries constrict and stop unnecessary flow into organs and tissues other than the brain and the heart. The aim is to send more blood to the brain. The veins constrict simultaneously, and the blood in their store is pumped first to the heart and then to the brain.
It is dangerous when an artery bleeds. It may lead to excessive bleeding because of the high blood pressure, and death could ensue. Conversely, a person does not lose much blood when a vein bleeds, for blood pressure is virtually non-existent in the veins. Surgeons are especially careful about puncturing an artery during an operation because it is hard to stop the blood that spurts out of the arteries.
The arteries are not found close to the skin; but are located deep under the skin. The arteries, especially those in the arms and legs, pass from among the muscles so that they cannot be easily harmed. The veins are created immediately beneath the skin. Bleeding of a vein does not pose a huge threat as bleeding of arteries.
A question may tug at your mind at this point: why aren’t both vessels created deeper and thus protected?
Nurses cannot use the arteries when they administer medicine, blood, or serum because the arteries refuse blood from outside due to the high pressure. Therefore, only the veins accept serum or blood externally. As the veins are in plain sight right under the skin, the job of nurses is made easier. The jobs of surgeons also becomes easier because the arteries lie deep within and the veins lie along the surface.
The arteries do not have valves to stop the reverse flow of blood because the blood is already pumped with high pressure. There are valves only between the heart and the arteries. If it weren’t for these valves, the blood pumped from the heart would flow back, causing heart failure, and the brain would not receive blood. The veins by contrast are equipped with valves to stop blood from flowing back.
When we move our legs, the blood is jammed in the veins. The closing direction of the valves are placed so as to lead to the upward movement of the blood. When we move, the blood in our legs moves upward and when we stop moving the blood does not flow back down because the valves close with the end of the movement. The valves in our veins are present only in those that are below the heart. There is no valve in the vessels above the heart, as they would be rendered useless due to gravity.
We rarely think about our veins and arteries, but they have been perfectly created to serve our body.