formation of tissue fluid

• when an artery reaches the tissues, it branches into smaller arterioles, and then into a network of capillaries. These eventually link up with venules to carry blood back to the veins. Thus, blood flowing into an organ or tissue is contained in the capillaries.
• At the arterial end of a capillary, the blood is at a relatively high hydrostatic pressure; this pressure tends to push the blood fluid out of the capillaries via the capillary wall. The fluid can leave through the tiny gaps between the cells in the capillary wall
• The fluid that leaves the blood consists of plasma with dissolved nutrients and oxygen. All the erythrocytes, platelets and most of the white blood cells remaining the blood and also the plasma proteins too. These cells are too large to be pushed through the gaps in the capillary wall.
• This tissue fluid surrounds the body cells so that gases and nutrients can exchange across the plasma membranes via diffusion, facilitated diffusion, and active transport. Oxygen and nutrients enter the cells and carbon dioxide and other waste leave the cells.
• the blood pressure at the venous end of the capillary is much lower. this allows some of the tissue fluid to return to the capillary carrying carbon dioxide and other waste products into the blood.
• At the venous end of the capillary, not all tissue fluid re enters into the blood:

  • Some tissue fluid is directed into the lymphatic system
  • This drains the excess tissue fluid out of the tissues and returns it into the blood system in the subclavian vein in the chest
  • The fluid in the lymphatic system is called lymph, it is similar to tissue fluid in composition but it will contain more lymphocytes which are produced in the lymph nodes