Diseases of the Lymphatic System

The adult human body is made up of 60% water and is divided into extracellular and intracellular fluid compartments. Extracellular fluid is present outside the cells and makes up â…“ of the total body water. Intracellular fluid is present inside the cells and makes up â…” of the total body water. Intracellular and extracellular fluids are separated into compartments by semipermeable membranes, and the transport of fluid and ions is maintained by channels in the cell membrane. Each compartment contains different concentrations of ions and osmolar molecules. The relative charge and osmolarity are maintained rigorously by the transport of water and substances between compartments. Hypernatremia, hyponatremia, and edema are the clinical conditions arising from disturbances in the maintenance of osmolarity of the body fluid compartments.

Lymphatic filariasis, also known as elephantiasis, is a chronic mosquito-borne infection caused by Wuchereria bancrofti, Brugia malayi, and B. timori. The majority of causes are due to W. bancrofti. Mosquitos are the vectors, and humans are the primary reservoir. Patients with acute infection can present with fever, adenolymphangitis, dermatolymphangioadenitis, and tropical pulmonary eosinophilia. Patients with chronic infection present with lymphedema, which commonly affects the lower extremities (but can cause testicular swelling or hydrocele). Long-term effects also include renal manifestations. Thick and thin peripheral blood smears are the mainstay of diagnosis. Lymphatic filariasis without co-infection is generally managed with diethylcarbamazine. Prognosis is good with early diagnosis and intervention. Elephantiasis, or late-stage lymphedema, is associated with significant disability and would require different methods (including surgery) to reduce swelling and complications.

Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. Fluid dynamics in the body depend on body fluid compartments, fluid osmolarity, and Starling forces. Edema can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Symptoms vary depending on location of the edema.

The primary lymphoid organs, also referred to as central lymphoid/lymphatic organs, are the tissues responsible for the production of lymphoid cells from progenitor cells, incuding the bone marrow and the thymus. In the bone marrow, hematopoietic stem cells progress to become oligopotent progenitors (in the case of lymphocytes, the common lymphoid progenitor). B lymphocytes stay and undergo processes for differentiation before migrating to the secondary lymphoid organs (such as lymph nodes). The progenitor cells that are to become T lymphocytes proceed to the thymus for further maturation.

The secondary lymphoid organs, also called peripheral lymphoid/lymphatic organs, include MALT, the lymph nodes, and the spleen. These collections of lymphoid tissues provide constant surveillance for pathogens. In their distinct sites, these tissues are filled with immune cells ready to mount a response when antigens are detected. Lymph nodes are seen along lymphatic vessels and occur as chains or groups (neck, groin, axillae, mesenteries, abdomen). MALTs act as immune sensors situated in locations where the lumen is exposed to the external environment (oropharynx, GI tract, genitourinary tract). The spleen is the site of production of antibodies and lymphocytes, but it also aids in the breakdown of platelets and erythrocytes.

The lymphatic system consists of the lymphoid organs containing the cells of the immune system and the lymphatic vessels, which transport interstitial fluid (as lymph) back to the venous circulation. Lymphatic vessels are spread extensively throughout the body, draining and filtering lymph, facilitating homeostasis, and aiding in defense against circulating pathogens. Fluid flow is unidirectional, enabled by valves in the collecting lymphatic vessels. In vessels without valves, the muscle contraction of organs and adjacent blood vessels help in the fluid movement. To return to the venous circulation, the lymph is collected by the major lymphatic ducts: right lymphatic duct (collects from the right side of the head and neck, the right side of the thorax, and the right upper extremity) and the thoracic duct (collects from the rest of the body). Pathologic conditions involving the lymphatic system are associated with infections, lymphatic damage, or injury and malignancies.