Tissue Fluid (Cambridge O Level Biology)

• Plasma is a straw-coloured liquid that constitutes around 55% of the blood
• Plasma is largely composed of water (95%) and because water is a good solvent, many substances can dissolve in it, allowing them to be transported around the body
• As blood passes through capillaries, some plasma is forced out (under pressure) through gaps in the walls of the capillary to surround the cells of the body
  • This results in the formation of tissue fluid

• The composition of plasma and tissue fluid are virtually the same, although tissue fluid contains far fewer proteins
  • Proteins are too large to fit through gaps in the capillary walls and so remain in the blood

• Tissue fluid bathes almost all the cells of the body outside of the circulatory system
• The exchange of substances between cells and the blood occurs via the tissue fluid
  • For example, carbon dioxide produced in aerobic respiration will leave a cell, dissolve into the tissue fluid surrounding it, and then diffuse into the capillary
  • This is how all substances are exchanged between cells and their surroundings in large, multicellular organisms

Formation of Tissue Fluid Diagram

Formation of tissue fluid