Human Lymphatic System


The lymphatic system is closely associated with both the immune system and the circulatory system.

Structure of the lymphatic system:

  • Lymph
  • Lymph vessels
  • Lymph nodes
  • Spleen
  • Tonsils
  • Adenoids
  • Lacteals
  • Thymus gland

Lymph: clear liquid that is collected from around cells and is transported by the lymphatic system back to the bloodstream.

Lymph vessels: narrow, dead-ending tubes that transport lymph and are present in every tissue and organ throughout the body.

Lymph nodes: small, spherical-shaped organs of the lymphatic system that contain many white blood cells.

Spleen: organ located just underneath and to the left of the stomach that functions in the maturation of lymphocytes and filtering out bacteria, viruses and abnormal cells.

Thymus: specialised lymphatic organ located just in front of the heart and behind the sternum. It functions in the maturation of lymphocytes. It also produces the hormone thymosin (see Chapter 38).

Adenoids and tonsils: the adenoids are located at the back of the nasal cavity while the tonsils are located at the back of the mouth on either side. They function in killing pathogens during an infection. For example, the tonsils can become sore and swollen during colds, flu and throat infections; the adenoids also become swollen during an infection (such as a cold) and give the feeling of a ‘blocked nose’.

Functions of the Lymphatic System

  • Collects extracellular fluid and returns it to the blood stream at the subclavian veins.
  • The lymph nodes filter lymph removing bacteria, viruses, abnormal cells and cell debris.
  • Absorbs fat from the small intestine.
  • Maturation of lymphocytes.