page_title: Digestion
section_title: Release of outer membrane vesicles
hierarchical_section_title: Digestion / Digestive system / Secretion systems / Release of outer membrane vesicles
context_page_description: Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substances are absorbed through the small intestine into the blood stream. Digestion is a form of catabolism that is often divided into two processes based on how food is broken down: mechanical and chemical digestion. The term mechanical digestion refers to the physical breakdown of large pieces of food into smaller pieces which can subsequently be accessed by digestive enzymes. In chemical digestion, enzymes break down food into the small molecules the body can use.
  In the human digestive system, food enters the mouth and mechanical digestion of the food starts by the action of mastication, a form of mechanical digestion, and the wetting contact of saliva. Saliva, a liquid secreted by the salivary glands, contains salivary amylase, an enzyme which starts the digestion of starch in the food; the saliva also contains mucus, which lubricates the food, and hydrogen carbonate, which provides the ideal conditions of pH for amylase to work.
context_section_description: In addition to the use of the multiprotein complexes listed above, Gram-negative bacteria possess another method for release of material: the formation of outer membrane vesicles.  Portions of the outer membrane pinch off, forming spherical structures made of a lipid bilayer enclosing periplasmic materials.  Vesicles from a number of bacterial species have been found to contain virulence factors, some have immunomodulatory effects, and some can directly adhere to and intoxicate host cells.  While release of vesicles has been demonstrated as a general response to stress conditions, the process of loading cargo proteins seems to be selective.
caption: Venus Flytrap (Dionaea muscipula) leaf
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