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How are lymphatic capillaries different from blood capillaries?

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Diagram of the human lymphatic system highlighting lymphatic vessels and major lymphoid organs, including lymph nodes, adenoids, tonsils, thymus gland, spleen, appendix, bone marrow, and ducts. — lymphatic system The human lymphatic system, showing the lymphatic vessels and lymphoid organs.

While both blood and lymphatic capillaries are minute vessels involved in fluid transport, they serve distinct functions within the body's circulatory system and lymphatic system.

Blood capillaries are integral to the exchange of oxygen, nutrients, and wastes between the blood and bodily tissues. They form dense networks that connect arterioles to the venous system, allowing for the diffusion of substances across their thin endothelial walls.1

In contrast, lymphatic capillaries function as a drainage system. As blood circulates, plasma leaks into the tissues, becoming interstitial fluid. Lymphatic capillaries collect this excess fluid, along with proteins and particulate matter that are not reabsorbed by blood capillaries, and transport it as lymph back toward the bloodstream. While blood capillaries are found throughout nearly all tissues to support metabolic needs, lymphatic capillaries are absent in specific regions such as the central nervous system and bone marrow.2