The lymphatic system is a network of tissues and organs that help rid the body of toxins, waste, and other unwanted materials. The key function of the system is to transport lymph, a fluid containing infection-fighting white blood cells, throughout the body. It helps to maintain the fluid balance in the body by collecting excess fluid and particulate matter from tissues and depositing them in the bloodstream.
Human Lymphatic System
The lymphatic system is made up of a large network of lymph, lymphatic vessels, lymph nodes, lymphatic or lymphoid organs, and lymphoid tissues. It is not a closed system. 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 lymph nodes are found from the head to around the knee area.
The lymphatic system has multiple interrelated functions:
- It absorbs and transports fatty acids and fats as chyle from the digestive system.
- It is responsible for the removal of interstitial fluid from tissues.
- It transports white blood cells to and from the lymph nodes into the bones.
- The lymph transports antigen-presenting cells, such as dendritic cells, to the lymph nodes where an immune response is stimulated.
The lymphatic system consists of a conducting network of lymphatic vessels, lymphoid organs, lymphoid tissues, and the circulating lymph. The lymphatic system is commonly divided into the primary lymphoid organs, which are the sites of B and T cell maturation, and the secondary lymphoid organs, which are further divided into lymphocytes.
- Primary lymphoid organs: Primary lymphoid organs include the thymus, bone marrow, fetal liver. In humans, the thymus and bone marrow are the key players in immune function. All lymphocytes are derived from stem cells in the bone marrow.
Stem cells destined to become B lymphocytes remain in the bone marrow as they mature, while prospective T cells migrate to the thymus to undergo further growth. Mature B and T lymphocytes exit the primary lymphoid organs and are transported through the bloodstream to the secondary lymphoid organs, where they become activated by contact with foreign materials.
- Thymus– The thymus is located behind the sternum in the upper part of the chest.
It is a bilobed organ that consists of an outer, lymphocyte-rich cortex and an inner medulla. The differentiation of T cells occurs in the cortex of the thymus. In the cortex of the thymus, developing T cells, called thymocytes, come to distinguish between the body’s components, referred to as “self,” and those substances foreign to the body, called “nonself” to fight off foreign organisms.
- Bone marrow– This is the soft, spongy tissue in the center of certain bones, such as the hip bone and breastbone. White blood cells, red blood cells, and platelets are made in the bone marrow.
2. Secondary lymphoid organs: Secondary lymphoid organs include the lymph nodes, spleen, and small masses of lymph tissue such as Peyer’s patches, the appendix, tonsils, and selected regions of the body’s mucosal surfaces. The secondary lymphoid organs serve two basic functions, they are a site of further lymphocyte maturation, and they efficiently trap antigens for exposure to T and B cells.
- Lymph nodes– The lymph nodes, or lymph glands, are small, encapsulated bean-shaped structures composed of lymphatic tissue.
The spleen is found in the abdominal cavity behind the stomach. The spleen filters blood. One of its main functions is to bring blood into contact with lymphocytes. The functional tissue of the spleen is made up of two types of cells: the red pulp and the surrounding regions of white pulp. The red pulp contains cells called macrophages that remove bacteria, old blood cells, and debris from the circulation. The white pulp contains great numbers of lymphocytes, i.e, both B and T lymphocytes.
- Mucosa-associated tissues– Another group of important secondary lymphoid structures is the mucosa-associated lymphoid tissues. These issues are associated with mucosal surfaces of almost any organ, but especially those of the digestive, genitourinary, and respiratory tracts, which are constantly exposed to a wide variety of potentially harmful microorganisms. Therefore they require their system of antigen capture and presentation to lymphocytes. For example, Peyer’s patches, which are mucosa-associated lymphoid tissues of the small intestine, sample passing antigens and expose them to underlying B and T cells.
- Lymphadenopathy– Enlarged lymph nodes are caused by infection, inflammation, or cancer. Common infections that can cause enlarged lymph nodes include strep throat, mononucleosis, HIV infection, and infected skin wounds.
- Lymphedema– Lymphedema can result from a blockage in the lymphatic system caused by scar tissue from damaged lymph vessels or nodes. It is also often seen when lymph nodes are removed during surgery or radiation to remove cancer. The buildup of lymphatic fluid is commonly seen in arms and legs. Lymphedema can be very mild or be quite painful, disfiguring, and disabling. People with lymphedema are at risk for serious and potentially life-threatening deep skin infections.
- Cancers of the lymphatic system– Lymphoma is cancer of the lymph nodes and occurs when lymphocytes grow and multiply uncontrollably. Cancerous tumors can also block lymphatic ducts or be near lymph nodes and interfere with the flow of lymph through the node.
- Lymphangitis– It is an inflammation of the lymph vessels.
- Lymphangioma– It’s a malformation in the lymphatic system. Lymphangiomatosis is the presence of multiple or widespread lymphatic vascular malformations.
- Intestinal lymphangiectasia– This is a condition in which loss of lymph tissue in the small intestine leads to loss of protein, gamma globulins, albumin, and lymphocytes.
- Lymphocytosis– It is a condition in which there is a higher than normal amount of lymphocytes in the body.
- Lymphatic filariasis– It is an infection caused by a parasite that causes the lymphatic system not to function correctly.
- Castleman disease– Castleman disease involves an overgrowth of cells in the body’s lymphatic system.
- Lymphangioleiomyomatosis– It is a rare lung disease in which abnormal muscle-like cells begin to grow out of control in the lungs, lymph nodes, and kidneys.
- Autoimmune lymphoproliferative syndrome– This is a rare genetic disorder in which there is a high number of lymphocytes in the lymph nodes, liver, and spleen.
- Mesenteric lymphadenitis– This is an inflammation of the lymph nodes in the abdomen.
- Tonsillitis– This is an inflammation and infection of the tonsils.