Tissue Fluid and the Lymphatic System

• Blood consists of red and white blood cells, platelets and plasma.
• Plasma is a watery yellow liquid containing dissolved substances such

  as glucose, amino acids, respiratory gases, plasma proteins and useful

  ions.
• The blood plasma fluid which leaks into the tissues is called tissue fluid.
• Some of the tissue fluid returns to the blood at the venous end of the

  capillary.
• Blood plasma to tissue fluid

  • Blood arriving at the arteriole side of the capillary bed is at a higher pressure than blood in the capillaries.

  • As blood is forced into the capillaries it undergoes PRESSURE FILTRATION and much of the plasma is squeezed out through the thin walls.

  • This liquid is now called TISSUE FLUID.

  • It is similar to blood plasma but differs as the large plasma proteins are left behind so tissue fluid does not contain proteins.
• Pressure filtration

  • Pressure filtration causes the plasma to pass through capillary walls into the tissue fluid surrounding the cells.

  • Tissue fluid supplies cells with glucose , oxygen and other substances.

  • Carbon dioxide and other metabolic wastes diffuse out of the cells and into the tissue fluid to be excreted.

  • Much of the tissue fluid returns to the blood by osmosis.

  • Lymphatic vessels absorb excess tissue fluid and return it as lymph to the circulatory system.
• Lymphatic System Vessels

  • Lymph vessels are found throughout our tissues

  • Fine vessels with

  – thin walls

  – and are closed at one end

  – possess valves

  • Take up excess tissue fluid

  – Now called lymph
• Lymphatic Vessels

  • General muscle movements gradually move lymph along vessels

  • Lymphatic vessels have valves

  – Keeps the lymph slowly flowing in one direction

  • Vessels gradually gather together and become larger and larger

  • The largest vessels eventually connect to our circulatory system at lymph nodes

  – Lymph is filtered here and drained back into our blood