The lymphatic system is responsible for the production, transport and filtration of lymph fluid throughout the body. In addition to its important circulatory functions, the lymphatic system also has important immunological functions.

lymphatic system

The network of lymph vessels is divided into:

  • Capillaries
  • Pre-collectors
  • Collectors
  • Trunks

The lymph capillaries form the beginning of the lymphatic system. Here, large molecules (proteins) and interstitial fluid are absorbed and flow towards the pre-collectors, which channel the lymph fluid into the larger collectors.

The collectors have valves similar to veins which determine the direction of flow. The lymph collector segment bordered by a distal and proximal valve is known as a lymphangion. Here, the lymph flow is supported by intrinsic contractions of the lymphangion which is regulated by the sympathetic nervous system and lymph volume.

  • Breathing (diaphragm)
  • Muscle contractions
  • Vasomotion (pulsation of arteries)
  • External compression

    • Manual lymphatic drainage
    • Short stretch bandages
    • Gradient compression garments

On its way into the circulatory system, lymph passes through lymph nodes, which are stationed throughout the body. While the axilla and inguinal areas are the most well known for lymph nodes, the head and neck also contain a large quantity, as do the intestines, which contain Peyer’s patches.

The main functions of the lymph nodes: 

  • Filter bacteria, toxins and dead cells
  • Produce lymphocytes for fighting infection
  • Concentrate and filter lymph fluid
  • Regulate protein concentration in lymph

Finally, the lymphatic fluid is returned to the circulatory system through the major lymphatic trunks, such as the thoracic duct. Approximately two liters of lymph fluid flow are collected and returned back into blood circulation every day.

Three main functions of the lymphatic system:

  • Fight infection: the lymphatic system transports a watery, clear fluid full of lymphocytes. Lymphocytes are infection-fighting cells. The colorless fluid is known as lymph. Lymph fluid can also appear clearish yellow to white in appearance, depending on how concentrated it is.
  • Lipid (fat) absorption: the lymphatic system absorbs lipids from the intestine and transports them to the blood.
  • Drain excess fluid: as the blood circulates through the body’s tissues, it leaves behind waste products such as proteins and fluids. Excess fluid is drained through capillaries and into the lymphatic system where it is filtered and returned to the blood.
lymph capillaries diagram