Lymphatic System

The lymphatic system comprises a network of lymphatic vessels that carry a clear fluid called lymph directionally towards the heart. It is a part of the circulatory system and a vital part of the immune system.

The lymphatic system consists of:

  • Lymph
  • Lymph vessels
  • Lymph nodes
  • Lymph organs (spleen and thymus)
  • Lymphoid tissue (tonsils)
  • Bone marrow

Interstitial or tissue fluid, which bathes the cells of the body, constantly leaks out through the permeable walls of the blood capillaries. Thus its composition is very similar to that of blood plasma. Some of the tissue fluid enters back into the bloodstream at the venous end of the capillaries. The remaining tissue fluid diffuses through the walls of the lymph capillaries and constitutes lymph. Lymph moves through lymph vessels and lymph nodes before returning to the bloodstream.


The lymphatic system performs the following functions:

Tissue drainage

Every day in the human body, about 21 litres of fluid from the plasma leaks from the arterial end of the capillaries and moves into the tissues. Most of this tissue fluid is absorbed back into the bloodstream at the venous end of the capillaries. However, about 3 to 4 litres of fluid is drained away by the lymphatic vessels. If this doesn’t happen, the tissues would swell and lead to the failure of the cardiovascular system.

Absorption in small intestine

The lymphatic vessels located in the villi of the small intestine help in the absorption of fat and fat-soluble substances.


Lymphocytes, the white blood cells which provide immunity to the body, develop and mature in the lymphatic organs. Since lymphocytes are produced in the bone marrow, it is also considered to be lymphatic tissue.

Topics in this section

  • Lymph
  • Lymph vessels
    • Lymph capillaries
    • Larger lymph vessels
      • Thoracic duct
      • Right lymphatic duct
  • Lymphatic organs and tissues
    • Lymph nodes
      • Structure of lymph nodes
      • Functions of lymph nodes
    • Spleen
      • Organs associated with the spleen
      • Structure
      • Functions
    • Thymus gland
      • Organs associated with the thymus
      • Structure
      • Function
    • Mucosa-associated lymphoid tissue (MALT)
  • Pathology associated with lymph vessels
    • Spread of disease
    • Lymphatic obstruction
  • Disease of lymph nodes
    • Lymphadenitis
    • Lymphomas
    • Malignant neoplastic metastases
  • Disorders of the spleen
    • Splenomegaly (enlargement of the spleen)
  • Diseases of the thymus gland