tissue fluid and lymph

• • tissue fluid is the fluid that surrounds cells in tissues
  • it's made from substances that leave the blood plasma e.g. oxygen, water and nutrients
  • cells take in oxygen and nutrients from the tissue fluid and release metabolic waste into it
  • in a capillary bed, substances move out of the capillaries into the tissue fluid by pressure filtration
• As fluid leaves

  The hydrostatic pressure reduces in the capillaries
• The oncotic pressure is generated by plasma proteins present in the capillaries


  • Lower the water potential
  • Water potential in the capillaries is lower than in the tissue fluid due to fluid loss from the capillaries and the high oncotic pressure
  • Some water re-enters the capillaries from the tissue fluid at the venule end by osmosis
• At the venules end


  The hydrostatic pressure is much lower in the capillaries than in the tissue fluid
• At the start of the capillary bed, at the arteriole end

  The hydrostatic pressure inside the capillaries is greater than the hydrostatic pressure in the tissue fluid, this forces fluid out of the capillaries and into spaces around the cells, forming tissue fluid
• not all the tissue fluid re-enters the capillaries at the venule end of the capillary bed - some excess tissue fluid is left over. This extra fluid eventually gets returned to the blood through the lymphatic system - a drainage system made up of lymph vessels
• 1. the smallest lymph vessels are the lymph capillaries
  2. once the fluid passes into the lymph vessels, it's called lymph
  3. valves in the lymph vessels stop the lymph going backwards
  4. lymph gradually moves towards the main lymph vessels in the thorax. Here it's returned to the blood, near the heart