Learn how arteries and veins work, and what makes them so unique, essential and different.
Through closed vessels the closed circulatory system transports blood. This includes the arteries, veins, and the capillaries. Blood vessels that start from the heart are arteries and vessels that carry blood back to the heart are veins.
Arteries are located deep in the body and have thick walls. Since their walls are thick and oblique muscles, they are highly elastic. When the heart contracts, pressure is exerted and blood flows from the arteries. This is why in the veins a pulse is not noticed but in the arteries it is noticed. This pulse can be checked by a physician by touching the carotid arteries present in the neck or the arteries present in the wrist. Arteries have reddish brown blood and this blood is filled with oxygen and nutrients. There are two types of arteries, pulmonary and systematic. When arteries branch, it gives rise to arterioles that help to transport blood to parts that the arteries cannot reach. In smaller parts of the body where blood is not able to be reached by arteries, their arterioles supply blood.
Veins - have thin walls and in the body they are superficially located. Veins are located below the skin in the hands, arms, and thighs. In these areas the veins are easily visible. Under the influence of capillary action, the blood flows in the veins. The blood that flows in humans is flowing against the gravitational force. In the inner walls there are valves so that the back flow of blood can be prevented. When the blood tends to flow downwards, these valves will close. Blood will always flow in one direction. The color of the blood in the veins is bluish red and the concentration of urea, carbon dioxide, and other waste is high. There are two types of veins, pulmonary and systematic. They can be deeply situated or can be superficially situated.
Function of arteries and veins
The basis of the circulatory system is formed by arteries. By means of blood transporting oxygen and nutrients to the body's cells, which is the main function. The main functions of the arteries include supporting chemical balance, eliminating carbon dioxide, enable movement of proteins, and other substances.
Deoxygenated blood is carried by the veins. They carry the blood to the heart from all the body parts. Umbilical veins and pulmonary veins are the two veins that perform different functions.
Differences between arteries and veins
Due to pressure, blood is received by the arteries. However, this pressure is lacking in the veins.
These are the differences:
- Structure- arteries have three muscle layers, and are thick and elastic. Usually, valves are absent in the arteries, they are instead at the base of the aorta and pulmonary artery semilunar valves. Arteries have narrow lumen. There are less elastic fibers in veins which makes them less elastic. Veins possess valves and have wider lumen.
- Thickness- since arteries have to bear systolic pressure, they have thick walls. Also, in order to propagate the pulse further, the muscle mass is more. This will increase the movement of the blood to the tissues. This is why you can detect your heart rate from your wrist.
- Location- in order to prevent any damage associated with injury, the arteries are located deep in the body. The organs will not be able to receive blood if they are damaged. With veins, there are lymph vessels that carry the waste in the tissues. This way their damage will not be as severe.
- Pressure- in arteries the pressure is more in comparison to the veins.
- Valves- since veins rely on capillary action, the back flow of blood is prevented by the valves. When sitting and standing, the blood pressure may vary as the gravitational pressure changes. The back flow of blood in veins can be prevented but in arteries this is not required.
- Color- due to oxygenated blood, arteries have a dark reddish blood, but veins are bluish red since they carry deoxygenated blood.
- Diseases- nutrition is carried by the arteries as the arteries have thick walls. When fat accumulates, there are chances of nutrition borne diseases. With veins, only physical damage or obstruction can cause issues.
For body’s physiological needs oxygen serves as a fuel. Every cells, tissues and body organs receive blood only when the heart pumps blood. The bloods vessels consist of arteries, veins and capillaries. Through them nutrients and blood travels to other body parts. Often the blood vessels are like the tree branches. Aorta is the main artery of the body and it branches into smaller blood vessels. The keep branching till fine blood vessels known as capillaries are formed. Due to their fine size it is easier to distinguish the capillaries. In general, the basic structure is almost the same in all three blood vessels. They consist of three layers:
The inner layer is supplied with nutrients by the outermost layer which is made of connective tissues. Many nerve networks are present in this layer. The middle layer is made of smooth muscle and the next is the innermost layer which is also made of connective tissues.
In one study the effect of hydralazine was observed on arteries and veins and it was found that arteries were more sensitive to it. Even though the basic structure is the same but still there are some differences. In order to adapt situations and to enable proper functioning all these three blood vessels have been morphologically modified. Following are some differences with respect to their characteristics, structure and function:
- General characteristics- the largest type of blood vessel is arteries and from the heart to the other parts of the body oxygenated blood is carried by them. On the other hand, larger lumen and many valves characterize veins. The deoxygenated blood is returned from different body parts to the heart by these veins and their function is enabled by their morphology.
- Body location- arteries are deeply located. The smooth muscle layers of the arteries that are present closer to the heart are thickest. Their muscle layer is thick since they have to bear the pressure exerted when from the heart blood is pumped. On the other hand, just beneath the skin veins are located but some may be deeply located. They are closer to the muscles so that the backflow of blood can be prevented. When contraction of muscle occurs, the veins compress and the blood is pushed forward by the walls of the veins. Also the backflow is hindered by the valves present in these veins.
- Wall of vessel- arteries have thick and strong walls and these walls have fibrous tissues, muscles and they are elastic in nature whereas the walls of the veins have less muscles, elastic fibers and mostly have fibrous tissues. Arteries have lesser fibrous tissues in comparison to veins.
- Types- arteries are of three types and these are conducting arteries, distributing arteries and smallest arteries. Further based on the size the conducting arteries are divided into larger and smaller arteries. They conduct oxygenated blood away from the heart. The largest artery is the aorta. Next is distributing artery as in those smaller and narrower locations where conducting arteries are not able to reach the distributing arteries distribute blood. The last one is arterioles. To the capillary bed they supply blood. This is the place where between the cell and the tissues the gas exchange takes place. Veins are divided into smaller veins known as venules and they help to drain the blood from the capillaries. As they go towards the heart through the larger vein they are transported and these are superior vena cava and inferior vena cava. Since inferior vena cava does the work of returning blood from all organs and tissues that are located below the diaphragm hence they are larger and the longer.
- Layers of vessel walls- there are three layers of arterial vessel wall and these are namely tunica adventitia, tunica media and tunica intima. The veins are also made of the same three vessel wall layers.
- Diameter of lumen- depending on the heartbeat the size of the lumen may vary but mostly it is the veins that have wide lumen.
- Valves- arteries have no valves but in order to prevent back flow of the blood veins have valves.
- Function- blood is carried away from the heart to the rest of the body by the arteries and blood is carried from different body parts to the heart by veins.
- Key feature- backflow of the blood is prevented by the strength and elasticity of the arteries. Smooth muscle tissue is present in the arteries so that the pressure during the blood flow can be prevented. When the blood pumps blood from the heart the pressure keeps changing. The diastolic and systolic are the times when blood is pumped. Changes in the arterial pressure causes changes in the pressure which can be felt when pulse rate is taken. The blood flows with less resistance due to the veins. Any changes in the blood volume can be tolerated and the veins have the capacity to hold up to 70 percent of body blood.
- Types of blood- oxygenated blood are transported by the arteries and deoxygenated blood is transported by the veins.
- Exception- all arteries carry oxygenated blood only pulmonary artery carries oxygenated blood. An exception to this is pulmonary artery. To the lungs blood is pumped by the pulmonary artery so that waste products can be removed and more oxygen can be received. Similarly, veins carry deoxygenated blood but the only type of vein that does not carry deoxygenated blood is pulmonary vein. Instead of carrying deoxygenated blood, from the lungs it carries newly oxygenated blood to the heart. Eventually through the arteries will be transported in the body.
- Color of blood- in the circulatory system oxygenated blood is transported by the arteries. This blood is transported from the left chambers of the heart and the pulmonary veins. Hemoglobin and oxygen merge with each other due to which the veins get their color. Differences between the deoxyhaemoglobin and oxyhemoglobin give the deoxygenated blood dark color. If the vein is 0.5mm deep, then from the outer side of the venous tissue scattered away blue light triggers the blue impression of the surface veins. Through the skin that is translucent the blood color looks purple.
- Miscellaneous characteristics- arteries have to exert higher pressure and veins exert low pressure the speed of blood flow in the arteries is fast whereas in the veins it is slow. Arteries have a distinct pathway of blood flow whereas in case of veins due to many interconnections the pathway becomes indistinguishable. The beat produced by arteries can be realized but same is not the case with veins. Arteries will still remain open if the flow of the blood stops but in case of veins they will right away collapse if the blood flow to the veins is stopped.
- Types of disease and disorders- arteries tend to enter into pathological state when the endothelial cells get impaired. The arterial walls may get thickened and form a plaque due to certain other trigger that may act as stimuli such as cholesterol, pathogens etc. Atherosclerosis, myocardial infarction and vasculitis are some of the diseases by which the arteries get affected. It is very difficult to diagnose disease and disorders associated with the veins since under low pressure veins pump blood. Most of the times when there is blood clot that causes blockage or venous blood drainage is inadequate then diseases of the veins occur. Often these diseases of the veins are very rarely dangerous, common and can be cured.
In order to understand the nature of the arteries and veins and their physiology one should decipher the differences between the both. This knowledge will help in therapeutic advancement and many therapies and treatment methods can be improved by this method.