Exocytosis

Exocytosis is a type of mass transport out of the cell. In this merge, " merge " in the cytosol lying vesicles with the cell membrane and enter as freely substances stored in them. The first connection between the lumen of the vesicle and the extracellular space is referred to as fusion pore. The exact nature of the fusion pore and the biophysical mechanisms of membrane fusion are still unclear. In purely physical act in the very near approach of two membranes huge repulsive forces. Nevertheless, for example, the exocytosis of synaptic vesicles takes place within a millisecond.

One can divide the exocytosis in two different ways:

Constitutive exocytosis

Via the constitutive or untriggered exocytosis membrane proteins are incorporated into the cell membrane and the biological membrane, comprising a lipid double layer, is renewed or extended. This process is also known as the cell membrane biogenesis. On the other hand, proteins in the extracellular matrix can be delivered via the constitutive exocytosis. This type of exocytosis is particularly important in cells of the connective and supporting tissue, such as fibroblasts and osteoblasts.

Stimulated exocytosis

The activation of the stimulated or triggered exocytosis requires a specific stimulus. Most of this stimulus is a hormone that binds to a specific receptor on the cell surface, thus a signaling cascade within the cell triggers, which then in effect, the fusion of the exosome with the cell membrane result.

This form of exocytosis plays an important role in the release of hormones into the blood and the release of digestive secretions in the chyme in the digestive system. An example is the delivery of insulin. In the insulin-producing cells ( islets of Langerhans in the pancreas ), the hormone molecules are packaged into vesicles and transported to the cell surface. There fuse ( merge ) the vesicles with the cell membrane and the insulin will make to the outside.

Also new plasma membrane components are from the Golgi apparatus - their manufacture - for membrane transport.

The basic operations are illustrated schematically in the following with reference to Figure 3. They play at the molecular level in the nanometer range and run with more intermediate steps from.

The exocytosis is at the molecular level is a complex interplay between a wide variety of molecules, and follows well-defined functional processes. However, it has proved in the course of evolution to be successful and effective.