Circulatory system

Arterial features

  • lumen

    • small to keep blood pressure high

  • endothelium

    • smooth to reduce friction

  • elastic fibres

    • recoil to keep blood under pressure and smooth out any pulses

  • smooth muscle

    • allows artery to stretch

    • controls blood flow to organs

  • collagen fibres

    • stops artery bursting under pressure

  • artery

Venous features

  • lumen

    • larger as blood is at lower pressure

  • endothelium

    • smooth to reduce friction

  • elastic fibres

    • thinner layer as blood under lower pressure - less recoil needed

  • smooth muscle

    • thinner layer as blood under lower pressure - less recoil needed

  • collagen fibres

    • protect veins as nearer to the surface so more likely to be damaged

  • vein

Capillary features

  • lumen

    • very small

    • only allows one cell through at a time

  • endothelium

    • permeable

    • WBC can pass through spaces between cells

    • short diffusion distance

    • smooth to reduce friction

  • capillary

blood vessels detailed

Macrovessels and microvessels

  • macrovessels

  • microvessels

Blood flow

  • Aorta → artery → arterioles → capillaries → venules → veins → vena cava

  • blood flow mechanism

Valves in veins

  • many veins pass between large muscles

  • as muscles move they squeeze the blood along the vein

  • valves prevent the backflow of blood when muscles relax

  • valves