Lymphatic vessels
Lymphatic vessels are thin-walled vessels that form a network throughout the body and are responsible for the transport of lymph, a clear fluid that contains immune cells, metabolic waste products, and other substances, from the tissues to the circulatory system. Lymphatic vessels are found in almost all tissues and organs of the body, except for the central nervous system, bone marrow, and avascular tissues.
Lymphatic vessels are similar in structure to blood vessels, but they are thinner and have more valves to prevent the backflow of lymph. The smallest lymphatic vessels are called lymphatic capillaries, which are blind-ended tubes that are located in the interstitial spaces of tissues. Lymphatic capillaries are lined with endothelial cells that overlap to form one-way valves that allow fluid and small molecules to enter but prevent their backflow.
As lymphatic vessels converge, they form larger vessels, which eventually empty into the thoracic duct or the right lymphatic duct, which then drain into the circulatory system at the subclavian veins. The lymphatic system lacks a pump like the heart, so the movement of lymph through the vessels is driven by the contraction of surrounding muscles, the pressure changes during breathing, and the contraction of smooth muscle in the walls of the lymphatic vessels.
The lymphatic system plays a critical role in the immune system and in maintaining fluid balance in the body. Disorders of the lymphatic vessels, such as lymphedema or lymphangitis, can lead to the accumulation of fluid in the tissues and an increased risk of infections. Treatment for lymphatic disorders depends on the specific condition and may include medications, compression therapy, or surgery.
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