VEINS

VEINS

1. bring/ return blood to the heart

2. blood pressure is very low

   • typically 5mm Hg or even lesser
   • How does blood move then?

3. three layered wall, just like arteries

   • except the low blood pressure means less elasticity is required
     • tunica media is much thinner and has far fewer elastic fibres

4. The blood is pushed by muscle contraction

   • when you tense muscles, they squueze inwards, temporarily rasing the pressure in veins

5. contain half moon/ semilunar valves

   • formed from the endothelium
   • allow blood to move towards the heart but not away from it
     • blood in the veins is squeezed up through the valves but can not pass down through them

6. used when

   • blood transfusions
   • collecting blood sample

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