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

LymphLymph vesselsLymph capillaries
Larger lymph vesselsThoracic ductRight lymphatic duct
Lymphatic tissues and organsLymph nodesStructure of Lymph Node
Functions of lymph nodesSpleenOrgans associated with the spleen
Structure of spleenFunctions of spleenThymus gland
Organs associated with thymusStructure of thymusFunctions of thymus gland
Mucosa-associated lymphoid tissue (MALT)Pathology associated with lymph vesselsSpread of disease
Lymphatic obstructionDiseases of lymph nodesLymphomas
Disorders of the spleenDiseases of thymus gland