Tissue Fluid

• Formation of tissue fluid from plasma


  1. Plasma leaks out through gaps in the walls of the capillary (fenestrations) to surround the cells of the body

  2. This results in the formation of tissue fluid
• Plasma


  A straw-coloured liquid that constitutes around 55% of the blood, largely composed of water (95%) which allows many substances to dissolve and be transported around the body
• The composition of plasma and tissue fluid are virtually the same, although tissue fluid contains far fewer proteins</b>
• Proteins


  Too large to fit through gaps in the capillary walls and so remain in the blood, maintaining a higher osmotic pressure compared to tissue fluid, preventing excessive fluid loss from the blood vessels into the tissues
• Tissue fluid bathes almost all the cells of the body outside of the circulatory system
• Uses of Tissue fluid


  • Nutrient Delivery
  • Waste Removal
  • Gas Exchange
  • Fluid Balance
  • Immune Response
• Nutrient Delivery


  Tissue fluid serves as a medium for transporting nutrients from the capillaries to the surrounding cells
• Waste Removal


  Tissue fluid can be used to carry away metabolic waste products produced by cells, such as carbon dioxide and urea
• Gas Exchange


  Oxygen and carbon dioxide exchange occur between the blood capillaries and the tissue fluid
• Fluid Balance


  Tissue fluid helps maintain fluid balance within the interstitial spaces of tissues, continuously exchanged with plasma across the capillary walls through filtration and reabsorption
• Immune Response


  Tissue fluid contains immune cells, such as lymphocytes and macrophages, which play a crucial role in the body's defence against pathogens and foreign substances
• Hydrostatic pressure


  Pressure that fluid exerts when pushing against the side of a vessel
• Oncotic pressure


  Pressure created by the osmotic effects of the solutes
• Fluid exchange at the arteriole end of the capillary

  Hydrostatic pressure in the capillary exceeds that of the tissue fluid, forcing fluid and dissolved substances out of the capillary and into the spaces around the cells, forming the tissue fluid
• Fluid exchange at the venule end of the capillary


  1. Water potential is lower inside the capillary compared to the tissue fluid, so water moves back into the capillary by osmosis

  2. Excess tissue fluid drains into the lymphatic system which eventually returns the fluid back into the bloodstream
• If blood pressure is high (hypertension)


  The pressure at the arteriole end is even greater, pushing more fluid out of the capillary and causing fluid accumulation around the tissues (oedema)
• Lymphatic system


  1. Tissue fluid re-enters capillaries

  2. Some tissue fluid enters lymph capillaries

  3. Lymph capillaries are separate from circulatory system

  4. Lymph capillaries have closed ends and large pores

  5. Large molecules enter lymphatic system as lymph

  6. Small valves in vessel walls are entry point to lymphatic system

  7. Liquid moves along larger vessels by compression from body movement

  8. Valves prevent backflow

  9. Lymph reenters bloodstream through veins close to heart

  10. Plasma proteins escaped from blood are returned to blood via lymph capillaries

  11. Lipids from digestion transported from intestines to bloodstream by lymph system
• Lymph capillaries


  • Separate from circulatory system
  • Have closed ends and large pores that allow large molecules to pass through
• If plasma proteins were not removed from tissue fluid they could lower the water potential (of the tissue fluid) and prevent the reabsorption of water into the blood in the capillaries