Reabsorption of tissue fluid

• Reabsorption:

  • Large molecules remain in the capillaries and therefore create a lowered water potential
  • Towards the venule end of the capillaries, the hydrostatic pressure is lowered due to the loss of liquid, but the water potential is very low
  • Water re-enters the capillaries by osmosis
• Once tissue fluid has exchanged metabolic materials with the cells it bathes, it is returned to the circulatory system. Most tissue fluid returns to the blood plasma directly via the capillaries.
• Tissue fluid returning to the blood plasma: HYDROSTATIC PRESSURE

  • The loss of the tissue fluid from the capillaries reduces the hydrostatic pressure inside them
  • By the time the blood has reached the venous end of the capillary, its hydrostatic pressure is usually lower than the tissue fluid outside it
  • Therefore tissue fluid is forced back into the capillaries by the higher hydrostatic pressure outside them
• Tissue fluid returning to the blood plasma: OSMOSIS

  • The plasma has lost water and still contains proteins. It therefore has a lower water potential than the tissue fluid
  • As a result, water leaves the tissue by osmosis down a water potential gradient
• The tissue fluid has lost much of its oxygen and nutrients by diffusion into the cells it bathed, but it has gained carbon dioxide and waste materials in return