What is arterial blood

Why do you take blood from the crook of your arm, of all places?

Dear Dr. Mo!

The last time I was with you, you took my blood - in the crook of your arm. Back at home I wondered why you took the blood there of all places. Couldn't it be picked up somewhere else too? For example on the wrist? You can also feel your pulse there - you should get much better access to the blood ...
Many greetings from Jan

Dear Jan,

there are several reasons why blood is drawn from the crook of the arm. To do this, you need to know something about the bloodstream: There are two different types of blood vessels in our body: Arteries and Veins.

In the arteries, the oxygen-rich blood is pumped away from the heart. That happens with a lot of pressure. You can even feel this pressure as a pulse in some parts of the body: for example on the wrist or neck. The doctor should not unintentionally stick his needle into an artery because the high pressure would literally squirt out the blood. The doctor only deliberately pricks an artery for special medical questions.

The deoxygenated blood flows back to the heart in the veins. The pressure is much lower here. If you stab a vein, blood will come out, but it won't splash. As a comparison, you can imagine a garden hose: If you put a needle in it while the water is turned on fully and flowing at high pressure, it splatters. If the water is only turned up halfway, it will run out of the needle hole.

There are more reasons for taking blood from the crook of the arm: In theory, blood could also be taken from the leg, for example - because there are veins all over the body. But that would be very cumbersome and impractical for you and me, you would have to take off your pants or roll them up, I would have to bend down, etc. In the crook of my arm, the veins are also close under the skin. They are relatively large and easy to see and feel. And there is another reason: in the crook of the arm, the nerve endings are not that close together. The puncture is less painful here than, for example, on the back of the hand. And it didn't hurt either, did it?
Best wishes,
Dr. Mon