This may have an obvious answer, but I can’t think of it;
In the summer blood vessels stick out above the skin a bit to cool the body down, but when I look at my arms I only see blue vessels, ie the de-oxygenated ones. So I guess my question is: why don’t red blood vessels rise above the skin?
Many thanks.
The red vessels carrying oxygenated blood are called arteries. You’ve probably heard about what happens if you cut even a fairly minor artery. In case you haven’t: arteries are maintained at pressure by both very elastic, muscular walls and by the force of the beating heat. If one is cut the blood squirts out under pressure. This makes it fairly hard for an arterial wound to clot and also leads to the loss of large volumes of blood in a short period of time. The result being serious blood loss, unconsciousness and death. Veins on the other hand carry deoxygenated (blue) blood back to the heart, aren’t under much pressure and gain what little pressure they have by a series of one-way valves and pressure derived from the muscles pushing them against other muscles, bone and the skin.
The practical upshot of all this is that animals’ arteries have evolved in such a way that they are buried deep inside the tissues, usually protected by bone, so that the risk of injury is minimised. Any animal that had major arteries that actually projected above the body surface would be just asking for death any time it got in a fight, walked through a briar patch, fell over etc. Veins on the other hand are often close to the surface so they can gain the maximum advantage from compression between the working muscles and the skin. Hence the reason you don’t see major red blood vessels.
Minor arteries (arterioles) penetrate all the body tissues (OK almost all, we’ll ignore the CNS) and do indeed come right up to the skin surface, they’re just so fine you can’t see them easily.
By and large blood vessels don’t stick out above the skins surface to cool you down. They stick out cause that’s where they are for other reasons. In cold weather the arteries/arterioles to the extremities contract to maintain core temperature, and since venous flow is proportional to arterial flow the veins are at a very low pressure and not easily seen. In warm weather when the arteries to the extremities dilate to remove excess heat from the core the venous pressure also rises and the veins become more prominent. But the arteries themselves don’t actually project at any time, and you’ll find the veins will project if you increase arterial flow to the limbs even in cold weather (try doing a couple of dozen curls in the cold and watch what happens to the veins).
For long, thin tropical people like me the phenomenon isn’t that pronounced. I can see dozens of raised veins on my fore-arm all year round because of my body type.
Gaspode,
Good explanation. Just one little thing.
[nitpick] The vessels that carry blood from the heart are called arteries. The vessels that carry blood returning to the heart are veins. Arteries carry the deoxygenated blood from the heart to the lungs and veins carry the freshly oxygenated blood back to the heart. The oxygenated blood leaves the heart via arteries to the rest of the body and deoxygenated blood returns to the heart via veins.[/nitpick]
Wouldn’t the carotid, brachial, and femoral arteries be exceptions to the “protected” rule? Granted, the brach. and fem. are on the inside (proximal?) surfaces of their respective limbs, but they’re still pretty easy to reach.
The carotid is an easy target too, but if something is attacking your neck you’ve probably already lost the fight.
I think you’re falling victim to the old myth that blood is actually “blue” inside the vein. Not true.
Deoxygenated blood isn’t blue! The blue colour is caused by the colour of the vessel itself. there is a small colour difference between oxygenated and deoxygenated but it is barely noticable (I think oxygenated is redder). Those probably are arteries as (you agree) veins are usually positioned around the skeletal muscles near the bones, ie deep in the skin as the contractions of the muscles help to push the blood back to the heart. Most arteries are totally unprotected. For example the carotid artery that goes through the neck. Anywhere you can feel your pulse, that is an artery on the surface.
As to funkynige’s original question, as far as I know, the veins sticking out is not used to cool down the body, the body has much better methods of cooling down than that, ie sweating.
from every corpse I’ve seen, including the ones that I’ve worked on in OMI and in my A&P lab the arteries and veins are the exact same color – the way to tell the difference between them is the construction of the two…veins are thin walled, have valves in them…arteries are much “beefer” because they have a muscular layer to allow for more give due to the high pressure envolved.
also, from my experience there are more veins closer to the surface than there are arteries…it is very easy to feel a vein – they are “spongy” or “bouncy” – a pulse is only palpable in specific locations, and even then can be hard to find and you have to push hard to get to it…a femoral pulse can be a bitch to find, and its a damn big artery. anywhere else the arteries are burried below other structures…its kinda hard to hide your radial pulse – there isint much room there to hide it.