tissue fluid

• ultrafiltration: small molecules filtered out due to high pressure
• at the arteriole end:

  high hydrostatic pressure

  net flow of fluid out of capillary to form tissue fluid

  
• at venous end:

  low hydrostatic pressure

  net flow of fluid back into capillary oncotic pressure of blood

  
• at the venous end, the pressure decreases because it's further away from the heart
• what causes the resistance to blood flow at the venous end?

  narrow lumen and total cross-sectional area is greater than the arterioles so the is more surface the blood will be in contact with
• some tissue fluid is reabsorbed and some is drained into the lymphatic system
• tissue fluid leaks out into capillaries
• uses of tissue fluid:

  • bathes cells of a tissue and allows exchange of substances between blood and cells
  • glucose, amino acids, fatty acids, salts and oxygen are all delivered to the cell
  • co2 and other waste substances are removed
  • composition is similar to blood plasma
• • blood contains erythrocytes and neutrophils
  • tissue fluid may contain neutrophils, but doesn't contain erythrocytes
  • formed from plasma by pressure filtration
  • all material exchanged between the blood and cells pass through the cell wall
  • fenestrations between endothelium cells are too small - erythrocytes can't shape too much