Blood Flow in Veins

Veins are the blood vessels that carry blood back to the heart from the tissues.

These tissues might be in the legs, arms, brain, liver, lungs etc.

Of course, it can easily be seen how blood returns from the brain - provided you are standing or sitting upright, gravity will do the work for you.

However, to get blood back to the heart from below it, the blood needs to be "pumped up" against gravity.

This is explained in more detail on the websites www.veins.co.uk and www.legulcers.co.uk as it is the understanding of the venous pump in the legs - and more importantly its failure - which leads to the problems of varicose veins, venous eczema, lipodermatosclerosis and venous ulceration. However, as far as an understanding of the veins is concerned in relation to deep vein thrombosis, we can concentrate on the flow in a patient at rest, who is lying down and whose flow is steady and not being pumped.

The vein wall has the same layers as the arterial wall, but it is much thinner. It is thinner as the flow is smoother and the vein wall does not have to withstand the pressure of the heart pumping.

The endothelium, intima and adventitia layers are much the same - the difference in the wall thickness is due to the the Media layer (the muscle layer) being much thinner.

Blood flows back to the chest from the legs through the veins.

As we have said, the blood is not being pushed back by the heart and so it has Low Pressure and fairly smooth Flow when you are lying down at rest.

It is for these 2 reasons that veins do not Pulsate - which is why you can't feel a pulse in the veins - only in the arteries.

Therefore,the important things to realise at this stage are:

1) Veins contain blood flowing smoothly and at low pressure

2) Veins have thin walls but still have endothelium next to the blood which stops the blood from clotting inside the vein.