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    lymphatic vessel

    lymph capillaries
    A vessel that, unlike a blood vessel, only carries fluid away from the tissues. The smallest lymphatic vessels are the lymph capillaries, which begin in the tissue spaces as blind-ended sacs. Lymph capillaries are found in all regions of the body except the bone marrow, central nervous system, and tissues, such as the epidermis, that lack blood vessels. The wall of the lymph capillary is composed of endothelium in which the simple squamous cells overlap to form a simple one-way valve. This arrangement permits fluid to enter the capillary but prevents lymph from leaving the vessel.

    The microscopic lymph capillaries merge to form lymphatic vessels, which are typically about as thick as a thread of cotton. Small lymphatic vessels join to form larger tributaries, called lymphatic trunks, which drain large regions. Lymphatic trunks merge until the lymph enters the two lymphatic ducts. The right lymphatic duct drains lymph from the upper right quadrant of the body. The thoracic duct drains all the rest.

    Like veins, the lymphatic tributaries have thin walls and have valves to prevent backflow of blood. There is no pump in the lymphatic system like the heart in the cardiovascular system. The pressure gradients to move lymph through the vessels come from the skeletal muscle action, respiratory movement, and contraction of smooth muscle in vessel walls.





    Main lymph vessels

    The two main lymph vessels are:
    1. The right lymphatic duct, which flows into the right subclavian vein.


    2. The thoracic duct, which begins in a small receptacle in the abdomen, called the cistern of Pecquet. All chyle-collecting vessels, which bring chyle from the small intestine, enter this receptacle as well. Lymph and chyle mix in the thoracic duct and flow into a large vein, known as the left subclavian vein, just before it reaches the heart.


    Related category

       • ANATOMY AND PHYSIOLOGY




    Source: National Cancer Institute



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