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Why the veins are blue if the blood is red

Why the veins are blue if the blood is red

In the arm, in the hands, in the neck, in the temples or even varicose veins, wherever we look our veins are of a clearly bluish color. This makes many people wonder why they appear in this color if the blood is red. The first logical answer could be to think that the veins are, in reality, blue, but we have already advanced that they are not. So, why are the veins blue if the blood is red?



Why the veins are blue if the blood is red

The blood is red, that is something that we all have clear and we have been able to prove convincingly. So, how is it possible that we see the blue veins? Are they really blue? The truth is that not all veins see blue, some see violet, others more reddish and others more greenish tone, either way, everything has an explanation.



The reason why we see the blue veins is an optical illusion. In fact, we only see blue those veins that are more superficial, those that are located half a millimeter below the skin, for example, the vein that crosses the arm and where we draw blood.


Why the veins are blue if the blood is red
Why the veins are blue if the blood is red

The fact is that the spectrum of light is formed by different wavelengths, and a different color corresponds to each length. When the light hits our skin, the largest lengths reach the deepest, while those that remain on the surface are the shortest. Taking into account that the waves of greater length are those of the red color and those of less length the blue ones, we have the answer to why we see the blue veins and, why, precisely, they are the most superficial ones. This is why the thinner the skin of a person and the less subcutaneous fat, that is, the closer the surface veins are located, the more blue they will look.



We have already explained that superficial veins are what we see blue, or rather, are what we see. But what are they? We must say that the veins of our body can be separated between those of the deep venous system and the main venous system:


Deep venous system: they carry more than 90% of the flow of blood, feed the muscles and most of the body’s functions.

Superficial venous system: they do not reach 10% of the blood flow, but they are all that we can see and feel. They are the ones that are located just below the skin.



Why the arteries are red and the blood blue

But the location of the veins is not the only reason, there is another that makes us see blue and is that, unlike the arteries, the veins themselves are really a bit more blue. The reason is that the blood that goes through the arteries is full of oxygen, erythrocytes and other cells that give it the reddish color while when it circulates through the veins have already been emptied and are somewhat more bluish.



In fact, this is what causes the arteries to be painted red and the veins are characterized by the blue color when the double system of blood circulation is drawn.



How are the veins

Arteries and veins have different characteristics, to begin with, they are constituted by three different layers:


Intimate layer: the most internal, which among other functions prevents blood clotting.

Adventitious layer: the outer one, where the nervous impulses are given.

Middle layer: the part that can contract, which is thicker in the arteries than in the veins, since in the first the blood has more pressure.


How veins work

The cells have the ability to contract, however, this contraction occurs involuntarily when certain circumstances occur. For example, with heat, the veins dilate to dissipate it, while in the cold they contract to conserve temperature.



The same thing happens depending on the blood pressure, which causes the veins to contract. This is precisely the reason why when we are stressed, anxious or when we get dizzy we become pale: because the veins contract and our skin loses the reddish coloration of the blood.


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