WRITTEN IN PART BY: The Editors of Encyclopedia Britannica. Last updated: 9-27-2017
Your Lymphatic System is a complex network of nodes, ducts and capillaries. Woven delicately throughout the body this system is fundamental to your body’s ability to heal from injuries and maintain a strong immune system.
The Lymphatic system can be thought of as a drainage system needed because, as blood circulates through the body, blood plasma leaks into tissues through the thin walls of the capillaries. The portion of blood plasma that escapes is called interstitial or extracellular fluid, and it contains oxygen, glucose, amino acids, and other nutrients needed by tissue cells.
Although most of this fluid seeps immediately back into the bloodstream, a percentage of it, along with the particulate matter, is left behind.
The lymphatic system removes this fluid and these materials from tissues, returning them via the lymphatic vessels to the bloodstream, and thus prevents a fluid imbalance that would result in the organism’s death.
The fluid and proteins within the tissues begin their journey back to the bloodstream by passing into tiny lymphatic capillaries that infuse almost every tissue of the body. Only a few regions, including the epidermis of the skin, the mucous membranes, the bone marrow, and the central nervous system, are free of lymphatic capillaries, whereas regions such as the lungs, gut, genitourinary system, and dermis of the skin are densely packed with these vessels. Once within the lymphatic system, the extracellular fluid, this is now called lymph, drains into larger vessels called the lymphatics.
These vessels converge to form one of two large vessels called lymphatic trunks, which are connected to veins at the base of the neck. One of these trunks, the right lymphatic duct, drains the upper right portion of the body, returning lymph to the bloodstream via the right subclavian vein. The other trunk, the thoracic duct, drains the rest of the body into the left subclavian vein. Lymph is transported along the system of vessels by muscle contractions, and valves prevent lymph from flowing backward. The lymphatic vessels are punctuated at intervals by small masses of lymph tissue, called lymph nodes, which remove foreign materials such as infectious microorganisms from the lymph filtering through them.
There are hundreds of lymph nodes in the human body. They are located deep inside the body, such as around the lungs and heart, or closer to the surface, such as under the arm or groin, according to the American Cancer Society. The spleen, which is located on the left side of the body just above the kidney, is the largest lymphatic organ, according to the U.S. National Library of Medicine (NLM). It controls the amount of red blood cells and blood storage in the body, and helps to fight infection. If the spleen detects potentially dangerous bacteria, viruses, or other microorganisms in the blood, it — along with the lymph nodes — creates white blood cells called lymphocytes, which act as defenders against invaders.
The lymphocytes produce antibodies to kill the foreign microorganisms and stop infections from spreading. Humans can live without a spleen, although people who have lost their spleen to disease or injury are more prone to infections. The thymus is located in the chest just above the heart, according to Merck Manual. This small organ stores immature lymphocytes (specialized white blood cells) and prepares them to become active T cells, which help destroy infected or cancerous cells.
After the skin, which is one of the body’s physical barriers to infections, part of the first line of defense, the lymphatic system plays a vital role in the other lines of defense, called the immune response. It includes the spleen, tonsils, thymus, lymph nodes, lymph vessels, other lymphoid tissues, and the clear, slightly sticky fluid called lymph.
Lymph is a clear and colorless fluid; the word “lymph” comes from the Latin word lympha, which means “connected to water,” according to the National Lymphadema Network.
Plasma leaves the body’s cells once it has delivered its nutrients and removed debris. Most of this fluid returns to the venous circulation through tiny blood vessels called venules and continues as venous blood. The remainder becomes lymph.
Unlike blood, which flows throughout the body in a continue loop, lymph flows in only one direction — upward toward the neck. Lymphatic vessels connect to two subclavian veins, which are located on either sides of the neck near the collarbones, and the fluid re-enters the circulatory system, according to the Mayo Clinic.
When bacteria are recognized in the lymph fluid, the lymph nodes make more infection-fighting white blood cells, which can cause swelling. The swollen nodes can sometimes be felt in the neck, underarms and groin, according to the NLM.
Lymphadenopathy is usually caused by infection, inflammation, or cancer. Infections that cause lymphadenopathy include bacterial infections such as strep throat, locally infected skin wounds, or viral infections such as mononucleosis or HIV infection. Inflammatory or autoimmune conditions occur when a person’s immune system is active, and can result in enlargement of lymph nodes.
The spleen, which is located on the left side of the body just above the kidney, is the largest lymphatic organ, according to the U.S. National Library of Medicine (NLM). It controls the amount of red blood cells and blood storage in the body, and helps to fight infection. If the spleen detects potentially dangerous bacteria, viruses, or other microorganisms in the blood, it — along with the lymph nodes — creates white blood cells called lymphocytes, which act as defenders against invaders.
The lymphocytes produce antibodies to kill the foreign microorganisms and stop infections from spreading. Humans can live without a spleen, although people who have lost their spleen to disease or injury are more prone to infections.
According to the Children’s Hospital of Pittsburgh of UPMC, when blood flows into the spleen, red blood cells must pass through narrow passages within the organ. Healthy blood cells can easily pass, but old or damaged red blood cells are broken down by large white blood cells. The spleen will save any useful components from the old blood cells, including iron, so they can be reused in new cells. The spleen can increase in size in order to store blood. The organ can widen or narrow, depending on the body’s needs. At its largest, the spleen can hold up to a cup of reserve blood.
The thymus gland, despite containing glandular tissue and producing several hormones, is much more closely associated with the immune system than with the endocrine system.
The thymus serves a vital role in the training and development of T-lymphocytes or T cells, an extremely important type of white blood cell. T cells defend the body from potentially deadly pathogens such as bacteria, viruses, and fungi.
The thymus is a soft, roughly triangular organ located in the mediastinum of the thoracic cavity anterior and superior to the heart and posterior to the sternum. It has two distinct but identical lobes that are each surrounded by a tough, fibrous capsule.
Within each lobe is a superficial region of tissue called the cortex and a histologically distinct deep region called the medulla. Epithelial tissues and lymphatic tissues containing dendritic cells and macrophages make up the majority of both regions of the thymus.
The function of the thymus is to receive immature T cells that are produced in the red bone marrow and train them into functional, mature T cells that attack only foreign cells. T cells first reside within the cortex of the thymus where they come in contact with epithelial cells presenting various antigens. The immature T cells that respond to the antigens corresponding to foreign cells are selected to survive, mature, and migrate to the medulla while the rest die via apoptosis and are cleaned up by macrophages. This process is known as positive selection.
Upon reaching the medulla, the surviving T cells continue to mature and are presented with the body’s own antigens. T cells that bind to the body’s own antigens test positively for autoimmunity, whereby they attack the body’s own cells instead of only foreign cells. Autoimmune T cells are eliminated by apoptosis in a process known as negative selection, resulting in only around 2% of the immature T cells reaching maturity.
Several hormones produced by the thymus promote the maturation of the T cells prior to their release into the bloodstream. The now mature T cells circulate through the body where they recognize and kill pathogens, activate B cells to produce antibodies, and store the memory of past infections.
Unlike most organs that grow until the age of maturity, the thymus enlarges throughout childhood but slowly shrinks from the onset of puberty and throughout adulthood. As the thymus shrinks, its tissues are replaced by adipose tissue. The shrinking is due to the reduced role of the thyroid in adulthood — the immune system produces most of its T cells during childhood and requires very few new T cells after puberty.
The thymus gland is intimately involved in our immune system, production of T Cells to fight off invading microorganisms. Thumping thymus boosts the immune system. Connecting thymus to other locations or systems, including the spleen, the electrical system, the “gut” via the navel and the hippocampus (part of the limbic system) is critical to building resiliency to dis-ease and boosting the immune function. We have learned the connection to the hippocampus-picture main heart electric point, spleen 21 points and the navel.