A fenestra (plural fenestrations or fenestrations) is a tiny aperture or pore that is often used as a word in the biological sciences. It is Latin meaning "window" and is used to define a pore in an anatomical structure in a variety of areas. Fenestrations are found in bones, especially those of mammals, where they provide pathways for blood vessels to reach muscle and other tissues. They can also be found in the wing membranes of some insects, where they allow air to pass while preventing water from entering. Fenestrations play an important role in respiration by allowing oxygen into cells and removing carbon dioxide out of them. They are also important in digestion because certain enzymes present in saliva are able to break down proteins and carbohydrates near blood vessels, which would otherwise be inaccessible to these enzymes. The presence of fenestrations allows nutrients to reach the cells surrounding the vessel wall, helping muscles and other organs function properly. In biology, the term fenestration usually refers to a perforation of some kind in an organ or bone, such as through a skull or vertebra. However, this article uses the term to refer to small pores exposed in skin or other tissue due to removal of the outer layer, such as when making windows in sardine cans to catch fish bait or to smoke foods without burning your house down.