The Lymphatic System

The lymphatic system consists of: lymphatic vessels which drain excess fluid from the tissues and return it to the cardiovascular system lymphatic organs such as lymph nodes, tonsils, spleen, thymus gland and red bone marrow that assist in immunity

This system has three main functions that contribute to homeostasis: Lymphatic capillaries take up excess tissue fluid and return it to the bloodstream Lacteals absorb fat from the digestive tract and transport them to the bloodstream The lymphatic system help defend the body against disease. This is carried out by white blood cells in the lymphatic vessels and organs.

Let’s draw a lacteal!

Lymphatic Vessels Most regions of the body are richly supplied with lymphatic capillaries. These capillaries are tiny, close ended vessels that take up excess tissue fluid. The fluid inside lymphatic vessels is known as lymph. Lymph is composed mostly of water, but it also contains solutes (eg. nutrients, electrolytes, oxygen).

The lymphatic capillaries join to form lymphatic vessels which lead to one of two ducts: The large thoracic duct – returns lymph from the lower body and left side of the body to the left subclavian vein. The right lymphatic duct - returns lymph from the upper body and right side of the body to the right subclavian vein.  

Lymph is moved through the vessels largely by skeletal muscle contraction. Vessels contain valves to prevent backflow. If fluid is not collected from tissues by the lymphatic system, swelling occurs which is known as Lymphedema.

Lymphatic Organs Lymphatic organs contain large numbers of lymphocytes (B cells and T cells) which help our body fight off foreign agents. The lymphocytes are produced and mature in the red bone marrow and the thymus.

Red bone marrow: site of stem cells which are capable of dividing and producing blood cells. Where B cells and T cells are produced Only B cells mature here

Thymus gland: Located in the thoracic (chest) cavity above the heart. Filled with maturing T cells Spleen Located in the upper left side of the abdominal cavity. Filters the blood Removes old and defective blood cells Cleanses the blood of foreign particles

Lymph nodes Small, oval structures occurring along lymphatic vessels which cleanse lymph. Packed with B cells and T cells which attack pathogens, fight off infections and attack cancer cells. When lymph nodes are swollen or tender it is a sign that they are fighting infection.