arteries, veins and capillaries

• arteries carry high blood pressure blood from the heart to the organs in the body this is because they have thick muscular walls they also carry blood away from the heart
• blood travels through the artery in surges (pulses) everytime the heart beats. to cope with this arteries have elastic fibres that stretch everytime a surge of blood passes through and then recoil between surges to keep the blood moving
• • capillaries have permeable walls so substances can move across them - capillaries have thin walls so the diffusion path is very short this allows substances to diffuse rapidly between the blood and body cells
• veins have thin walls they carry blood towards the heart . the lumen is wide so the blood pressure is low and slow . veins also contain valves to stop the backflow of blood