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Scanning electron mocrograph of a liver sinusoid with fenestrated endothelial cells. Fenestræ are approx 100 nm diameter, and sinusoidal width 5 micrometres. Original magnification 30,000

Fenestræ (singular: fenestra) are small pores in epithelial cells to allow for rapid exchange of molecules between blood vessels and surrounding tissue. These pores can 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 or other bones. Fenestræ is the Latin plural for windows.

See also

• Temporal fenestra

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