Tissue Fluid

• Tissue fluid Pt 1

  1 - capillaries only one cell thick so have tiny gaps between the cells in which liquid and small molecules can be forced out

  2 - At the arterial end water, glucose, amino acids and small proteins, fatty acids , ions and oxygen are forced out (ultrafiltration) due to capillaries having a smaller diameter so there is an increase in hydrostatic pressure (red blood cells, platelets and large proteins remain in the capillary).
• Tissue fluid Pt 2

  3 - At the venule end, water potential is very negative so water (and dissolved waste molecules like carbon dioxide and urea) can be reabsorbed via osmosis

  4 - rest of the tissue fluid (equilibrium restored in capillary so cannot go back in) absorbed into lymphatic system where it is reabsorbed into the blood stream near the heart.
• A higher salt concentration in the blood means a higher blood pressure so more fluid is pushed out at the arterial end of the capillary. This decreases the water potential in the tissue fluid so less water returns to the capilary by osmosis at the venule end.