• Tissue fluid is the liquid that surrounds the cells allowing for transport of molecules such as respiratory gases between the blood and the cells
  • Capillaries have a one cell thick wall, they are highly branched to increase their surface area. The capillaries walls are partially permeable.
  • Tissue fluid is the result of interplay of:
      Pressure
      Osmosis
  • Blood pumped from the heart reaches the capillaries and as pressure still remains high, hydrostatic pressure occurs at the arterial end of the capillary.
  • Hydrostatic pressure results in the tissue fluid to leave the blood plasma.
  • However, the outwards pressure is opposed by:
  • Hydrostatic pressure of the tissue fluid outside the capillary, which resists the outward of liquids
  • Lower Water Potential of the blood due to the plasma proteins causing water to move back into the blood within the capillaries

 

Structure
 

  • However, the overall force is to create and overall pressure that pushes the tissue fluid out of the capillaries at the arterial end
  • At the Venous end, the osmotic pressure and the net pressure is higher than the pressure within the capillary, therefore molecules diffuse enter the blood plasma
  • The overall net fluid movement is greater out of the artery end compared to the movement of fluid in. The net pressure is 10mm Hg at the arterial end compared to -7mm Hg at the venous end.
  • Any remaining tissue fluid is removed through the lymphatic system which restores the fluid back into the blood.