Lymphatic

Lymphatic refers to the lymphatic system, a network that complements the circulatory and immune systems. It includes lymph, lymphatic vessels, lymph nodes, and lymphoid organs such as the spleen and thymus. The system collects interstitial fluid and proteins that have leaked from capillaries and returns them to the bloodstream, helping to maintain tissue fluid balance and contribute to immune defense.

Lymphatic vessels begin with blind-ended lymphatic capillaries in most tissues. These capillaries merge into larger collecting vessels that have valves and smooth muscle to move lymph, aided by muscle contractions and body movement. Lymph from the lower body and left side of the body typically drains into the thoracic duct; the right lymphatic duct drains the right side of the head, neck, and thorax. Both ducts empty into the venous circulation at the subclavian veins.

Lymph nodes filter lymph and host immune cells; exposure to antigens triggers immune responses. Lymphoid organs such as the spleen, thymus, bone marrow, tonsils, and mucosa-associated lymphoid tissue participate in lymphocyte development and immune surveillance. Lymph also contributes to the absorption of fats and fat-soluble vitamins via specialized intestinal vessels called lacteals.

Clinical relevance: lymphedema results from impaired lymph drainage, causing swelling. Infections can cause lymphadenitis. The lymphatic system can serve as a route for cancer metastasis, and lymphomas are cancers of lymphocytes. Diseases of the lymphatic system are evaluated with imaging and, when needed, biopsy of lymph nodes.