Formation of tissue fluid

• Formation: Ultrafiltration

  • Capillaries have small gaps in the walls so that liquid and small molecules can be forced out
  • As blood enters the capillaries from arterioles, the smaller diameter results in a high hydrostatic pressure so water, glucose, amino acids, fatty acids, ions, and oxygen are forced out
• What remains in the capillary:

  • Red blood cells
  • Platelets
  • Large proteins

  (Molecules that are too large to be forced out of the capillaries tiny gaps)
• Tissue fluid is not red in colour because there are NO red blood cells, as they remain in the capillary (not forced out by hydrostatic pressure)