blood vessels

blood vessels

1. artery

   • elastic layer
     • thick
       • keeps blood pressure high
         • stretch and recoil prevents surges in pressure
       • overall to resist bursting under pressure
   • muscle layer
     • thick
       • smaller arterioles can be constricted + dilated
         • control volume of blood passing through
         • most pressure is absorbed by artery walls so less elastic fibres
   • valves/lumen
     • no valves as blood never flows backward bc of high pressure

2. vein

   • muscle layer
     • thin
       • carry blood from tissues, cant control it and slower
   • elastic layer
     • thin
       • blood pressure is low, no recoil action
   • valves/lumen
     • semi-lunar valves throughout
       • pressure is low so prevents backflow

3. capillary

   • numerous and highly branched + high SA
   • penetrate all organs and tissues
     • exchange between blood and cells
   • collects in venues then returned to veins
     • from arteries then arterioles
   • one cell thick endothelium = short DD + rapid diffusion
   • allows metabolic exhange
     • between blood and tissue fluid
       • flow of blood is much slower