Caveola

An tiny pit, grotto, depression, incupping in the surface of a cell. The name "caveola" means little cave. The plural is caveolae. Caveolae normally function to facilitate the uptake of fluid by the cell. In the process of pinocytosis, the caveolae close and pinch off to form pinosomes, little fluid-filled bubbles within the cell. Bacteria can hide in caveolae. Normally when bacteria enter cells, they go into compartments that fuse with cell structures called lysosomes in which they are destroyed. Caveolae do not fuse with lysosomes. The bacteria nestled in a caveola can thus escape extermination.

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A small pocket, vesicle, cave, or recess communicating with the outside of a cell and extending inward, indenting the cytoplasm and the cell membrane. Such caveolae may be pinched off to form free vesicles within the cytoplasm. They are considered to be sites of uptake of materials into the cell, expulsion of materials from the cell, or sites of addition or removal of cell (unit) membrane to or from the cell surface. [L.]

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ca·ve·o·la (ka-ve-oґlə) pl. caveoґlae [L.] a small (approximately 50 nm), flask-shaped invagination of the plasma membrane occurring in nearly all animal cells, coated with the membrane protein caveolin and rich in cholesterol and sphingolipids. Caveolae are a special form of lipid raft and are associated with endocytosis, budding from the plasma membrane to form pinosomes; they also concentrate signaling molecules and have been implicated in other processes, including the export of cholesterol to serum lipoproteins. Called also plasmalemmal vesicle.