• In histology, fenestræ are small pores in endothelial cells that allow for rapid exchange of molecules between sinusoid blood vessel
  Sinusoid (blood vessel)
  A sinusoid is a small blood vessel similar to a capillary but with a fenestrated endothelium. Fenestrations are pores in the endothelial cells that greatly increase their permeability. In addition, permeability is increased by large inter-cellular clefts and fewer tight junctions...
  
  s and surrounding tissue. These pores may enlarge and contract at the action of various stimuli such as noradrenaline.
• In anatomy, the term is used to refer to natural (as opposed to traumatic) openings in the skull
  Skull
  The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
  
   or other bone
  Bone
  Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
  
  s.

See also

• Temporal fenestra
• Sinusoid (blood vessel)
  Sinusoid (blood vessel)
  A sinusoid is a small blood vessel similar to a capillary but with a fenestrated endothelium. Fenestrations are pores in the endothelial cells that greatly increase their permeability. In addition, permeability is increased by large inter-cellular clefts and fewer tight junctions...
  
  
• Liver sinusoid
  Liver sinusoid
  A liver sinusoid is a type of sinusoidal blood vessel that serves as a location for the oxygen-rich blood from the hepatic artery and the nutrient-rich blood from the portal vein....