Bleb (cell biology)
In cell biology, a bleb is a protrusion, or bulge, of the plasma membrane of a cell, caused by localized decoupling of the cytoskeleton from the plasma membrane. Blebbing or zeiosis is the formation of blebs.
Bleb growth is driven by intracellular pressure generated in the cytoplasm by the contractile cell cortex.
Bleb formation can be initiated in two ways: 1) through local rupture of the cortex or 2) through local detachment of the cortex from the plasma membrane.  This generates a weak spot through which the cytoplasm can flow, leading to the expansion of a bulge of membrane. The cytoplasmic flow is driven by hydrostatic pressure inside the cell.  
During apoptosis (programmed cell death), the cell's cytoskeleton breaks up and causes the membrane to bulge outward. These bulges may separate from the cell, taking a portion of cytoplasm with them, to become known as apoptotic bodies. Phagocytic cells eventually consume these fragments and the components are recycled.
Blebbing also has important functions in other cellular processes, including cell locomotion, cell division, and physical or chemical stresses. The types of blebs vary greatly, including variations in bleb growth rates, size, contents, and actin content. It also plays an important role in all five varieties of necrosis, a generally detrimental process. However, cell organelles do not spread into necrotic blebs.
In 2004, a chemical known as blebbistatin was shown to inhibit the formation of blebs. This agent was discovered in a screen for small molecule inhibitors of nonmuscle myosin IIA and was shown to lower the affinity of myosin with actin, thus altering the contractile forces that impinge on the cytoskeleton-membrane interface.
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