The walls of lymphatic vessels are similar to those of veins. Each is composed of three layers: an endothelial lining, a middle layer of smooth muscle and elastic fibers, and an outer layer of connective tissue. Also like those veins below the heart, the lymphatic vessels have semilunar valves, which help prevent backflow of lymph. Figure 16.3 shows one of these valves.
The larger lymphatic vessels lead to specialized organs called lymph nodes. (limf nodz) After leaving the nodes, the vessels merge to form still larger lymphatic trunks.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.