Differences between veins, arteries and capillaries
Veins, arteries and capillaries share a common characteristic: all three are blood vessels. Blood vessels carry and distribute blood throughout the body, forming the circulatory system.
This system, in human beings, is closed; thus, the blood circulates through the interior of this system of conduits, which we call blood vessels.
These three blood lines can be confused. However, they present notable differences in terms of their characteristics and functions. In this article we will know the 6 differences between veins, arteries and capillaries. In addition, we will explain in detail what each of them is and what function it exercises in our body.
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Differences between veins, arteries and capillaries: what is each?
In order to understand the differences between veins, arteries and capillaries, we are going to define what each of these blood vessels is (and what it is like). We will know its most relevant characteristics and its functions.
1. Veins
Veins are the blood vessels responsible for transporting blood from the different organs towards the heart. The first of the differences between veins, arteries and capillaries that we find is that the wall of the veins is thinner and less resistant than that of the arteries, as we will see later. However, capillaries are even finer than veins.
This is so (that the wall of the veins is thinner and less resistant) because the blood that circulates through the veins does so with less pressure than that exerted on the arteries.
Inside the veins we find valves, called venous valves (or semilunar valves) that act by preventing the backward movement of blood towards the organs of origin. As we will see, in the arteries there are also valves that perform the same function (to prevent the backward movement of blood).
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2. Arteries
The arteries are those blood vessels responsible for carrying the blood that leaves the heart to the different parts of the body (that is, towards the different organs). So, we just found another one of the differences between veins, arteries and capillaries: veins come out the organs to the heart, and the arteries do just the opposite (they exit the heart into the organs).
What are the arteries like and what characteristics do they present? They are formed by an elastic and resistant wall. This wall allows them to withstand the pressure with which the blood leaves our heart. When the heart contracts, the blood comes out suddenly, "shot", and collects in the artery. This artery, upon receiving blood, swells.
Then, what the walls of the arteries do is pressure the blood that cannot go back towards the heart, since there are valves that prevent it: the sigmoid valves. Thus, the blood is pushed forward, and begins its journey throughout the body. We can say, then, that it is thanks to this pressure that blood can circulate and distribute itself throughout the body.
Finally, comment that the walls of the arteries have a series of holes through which blood flows to the different tissues of the body.
3. Capillaries
Finally, Capillaries are the blood vessels responsible for exchanging different substances between the lumen of the capillaries and the cellular interstitium of the tissues. Its thickness is extremely thin (as we saw, another difference between veins, arteries and capillaries is that capillaries are the thinnest blood vessels).
In fact, its name ("capillary") comes from this very fine thickness, assimilating the thickness of a hair.
As for the capillary wall, it is made up of the endothelium, a single layer of cells. This layer allows the components of the blood to filter into the cells and the waste from the cells to the blood.
All the organs of our body have their own capillary system. Technically, the arteries "become" capillaries, since as they move away from the heart, they branch out into other finer vessels, reaching the organs in the form of capillaries. These capillaries join and create increasingly thick vessels, which are the veins and which have the function of returning blood to the heart, as we have seen previously-
The 6 differences between these blood vessels
Now that we have known the definitions and characteristics of each of these blood vessels, as well as some of the differences existing between them, we are going to synthesize the differences between the most important veins, arteries and capillaries (some we have already mentioned).
1. Blood pressure
The blood flowing through the arteries converts to a certain pressure (the pressure that "comes" from the heart); in the case of veins and arteries, on the other hand, this pressure does not exist.
2. Origin and destination
Another difference between veins, arteries and capillaries is the origin and destination of the blood: while in the veins the blood leaves the organs towards the heart, in the arteries leaves the heart to the organs; finally, in the case of capillaries, these are actually the "endings" of the arteries, which have branched out at the end of the organs (destination).
3. Wall thickness
The next of the differences between veins, arteries and capillaries is found in the thickness of their walls. Thus, while the arteries have the thickest walls of all, the walls of the veins are slightly thinner, and those of the capillaries are the thinnest of all. Furthermore, the capillary walls are not associated with muscle tissues.
4. Degree of flexibility
While the walls of the arteries are thick and resistant (it has the flexibility to return to its original shape when crushed), this is not the case in arteries and capillaries. Thus, the arteries are the only blood vessels capable of recovering their original shape in the event of a deformity or external force.
5. Presence of valves
The fifth of the differences between veins, arteries and capillaries refers to the presence of valves. Both veins and arteries have valves inside, which have the function of preventing blood from flowing backwards.
The valves of the arteries are called sigmoid valves and those of the veins, venous or semilunar valves. In the case of capillaries, these do not have valves.
6. Blood oxygenation
The blood carried by the arteries and capillaries is oxygenated blood (with oxygen); on the other hand, the blood in the veins is not oxygenated.
This is so because the veins carry blood to the heart, coming from other organs; therefore said blood has already transported oxygen through the body, that is, said oxygen has been "lost" (distributed) along the way.
Bibliographic references
Barderi, M.G. (1998): Biology: Cytology, Anatomy, Physiology, Genetics, Health and Disease. Editorial Santillana.
Tortora, G.J. and Derrickson, B. (2013). Principles of anatomy and physiology. Mexico. Panamerican Medical (13th ed.).
Vadot, I. and Dasi, M.S. (1976). Human Physiology: Circulation. Barcelona, Spain). Marban. SIDALC Alliance.