Unit 4: The circulatory and excretory systems                        1   2   3   4

3. The lymphatic system

The main functions of lymphatic system are:

   - To collect the excess of interstitial plasma and give it back to blood,

      so that it helps to keep the fluid balance.

   - To produce and transport lymphocytes (immune system cells),

      so that it helps to organism defence.

   - To absorb and transport some lipids that can not travel by blood

      from the intestine, so that it helps to nutrition.

It is formed by a circulating liquid (lymph) and a distribution system (lymphatic vessels). There is not an impulse pump in this case. Lymph flows forced by skeletal muscles contraction and gravity.

Lymph is a clear fluid very similar to blood plasma without proteins and richer in lipids and lymphocytes.

The lymphatic vessels are:

- Lymphatic capillaries 

  They are tiny blind-ended vessels which are distributed among the tissues

  (with the exception of central nervous system, bone marrow and

  non-vascular tissues such as epidermis and cartilage).

  Their walls are made by endothelium that allows them drain these tissues.

- Lymphatic veins

   Lymphatic capillaries join to form larger vessels the lymphatic trunks.  

  These vessels join again to form two lymphatic ducts,

  the right lymphatic duct (that ends in Right Subclavian vein) and the  

  thoracic duct (that ends in Left Subclavian vein)

  Lymphatic vessels has valves to avoid lymph goes back.

- Lymphatic nodes

     They are small and numerous organs located along the lymphatic vessels

  mainly in crossways and they are especially abundant in the neck,

  armpits and groins.

  Their function is to produce lymphocytes.

Other lymphatic organs are: tonsils, thymus and spleen. All of them produce and mature lymphocytes too.

There are other organs that produce lymphocytes, such as appendix, bone marrow and Peyer’s patches, but they are less important.

3.1. Why lymphatic vessels are also called lymphatic veins and not  

        lymphatic arteries?

3.2. What is the main difference between blood and lymphatic capillaries?

3.3. What are the relation between blood, lymph and interstitial plasma?

3.4. Listen and relate each sentence with the correspondent function

       of the lymphatic system: