The Role of the Lymphatic System

While most people are familiar with the circulatory system and its basic function, far fewer know that the body also contains another network of vessels: the lymphatic system. Originating in the spaces between blood vessels and cells, known as the interstitial tissue or connective tissue, the lymphatic vessels form a finely branched network throughout the body. The lymphatic system is responsible for absorbing most of the excess fluid from the tissues. It collects, transports and filters substances dissolved in the tissue fluid, known as lymph.

These substances may include blood proteins, metabolic waste products, inflammatory substances, toxins, as well as bacteria and viruses. Like the body's own waste removal system, the lymphatic system transports up to 10 litres of fluid from the tissues each day. It therefore plays an essential role in immune function, fluid balance, and the filtration and cleansing of body fluids.

Structure of the Lymphatic System

Starting with the tiny lymphatic vessels in the tissues, lymph is transported through progressively larger lymphatic vessels until it reaches the lymph nodes. The human body contains an estimated 500 to 700 lymph nodes, although the exact number varies from person to person. Lymph nodes play a vital role in the immune system. They filter out pathogens and cancer cells while also producing specialized immune cells called lymphocytes.

From the lymph nodes, the lymphatic vessels merge into larger lymphatic trunks, which eventually drain into the large veins near the heart. This returns the lymph fluid to the venous bloodstream.

How Lymph Is Transported

Lymph is transported through the lymphatic vessels by both active and passive mechanisms. In active transport, gentle contractions of the vessel walls move the lymph forward. In passive transport, contraction of the skeletal muscles compresses the lymphatic vessels, helping propel the lymph through the system. One-way valves within the lymphatic vessels ensure that lymph flows in only one direction—toward the heart.

A Healthy Lymphatic System

As blood circulates through the tiny blood capillaries in the body's tissues, proteins, fluid and other substances pass into the spaces between the cells. In a healthy lymphatic system, this excess fluid is collected by the blind-ended lymphatic capillaries and drained into the lymphatic system.

The lymph first enters the initial lymphatic capillaries, which merge into larger lymphatic vessels equipped with one-way valves. Along these larger vessels are lymph nodes, which filter the lymph and play an important role in the body's immune defence.

A Damaged Lymphatic System

Lymphedema can develop when lymphatic drainage is interrupted or impaired, or when the amount of fluid entering the tissues exceeds the capacity of the lymphatic system to remove it. Excess fluid then accumulates in the tissues and can no longer be drained effectively, resulting in swelling of the affected area. If lymph continues to build up in the tissues over time, inflammatory reactions may develop. This can lead to further damage to the lymphatic vessels and cause scarring and hardening of the surrounding tissue.

Medical Reference


https://pubmed.ncbi.nlm.nih.gov/15536876/

Back to Overview