Lymphatic endothelial cells are continuous but highly attenuated and have a discontinuous basement membrane. Their cytoplasm contains an assortment of organelles, caveolae, and mitochondria. The cytoplasm contains typical cytoskeletal proteins, including actin, intermediate filaments, and microtubules with the ability to form actin-bundle (stress) fibers. The cytoskeletal proteins facilitate active changes in cell shape, such as pseudopod projection, phagocytosis, and formation of adhesion site or cell migration, as in lymph angiogenesis. There is no conclusive evidence that such cytoplasmic motion by the endothelial cells can be translated into a contractile mechanism for the lumen of a lymphatic channel comparable to the smooth muscle action in contractile lymphatics. The major part of the lymphatic endothelial cells is firmly attached to the surrounding collagen matrix.
Lymphatic endothelial cells in culture express remarkably high levels of genes implicated in protein metabolism, sorting, and trafficking. Current analysis indicates that genes with high representation are those encoding proteins that control specificity of vesicle targeting and fusion, such as members of the SNARE family, rab GTPases, AAA ATPases, and sec-related proteins, reflecting the existence of an extensive caveolar system .
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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.