Fenestrados

Fenestrados is the term used to describe capillaries whose endothelial lining contains fenestrae, small pores that enable rapid exchange of substances between blood and surrounding tissues. The word comes from fenestra, meaning “window.” Fenestrated capillaries are a distinct type of microvascular endothelium, intermediate in permeability between continuous capillaries and sinusoids.

The defining feature is the presence of transendothelial pores called fenestrae. These pores are typically about 60–80 nanometers in diameter. In some tissues, fenestrae may have a thin diaphragmatic cover formed by specific glycoproteins, while in others they are non-diaphragmed, allowing relatively unrestricted flow of small molecules.

Fenestrated capillaries are found in tissues that require efficient exchange between blood and interstitial fluid. Notable locations include the kidneys (glomerular capillaries), the small intestine mucosa, various endocrine glands (such as the pituitary and adrenal glands), and the choroid plexus of the brain.

Functionally, the fenestrae facilitate the rapid transfer of water, ions, and small solutes, while restricting larger molecules and cells. This makes fenestrated capillaries crucial for filtration and absorption processes, such as renal filtration and nutrient uptake, as well as for hormone secretion in endocrine tissues.

Clinical relevance is linked to capillary permeability: alterations in the number or integrity of fenestrae can affect tissue exchange, influence inflammatory responses, and contribute to disease processes that involve vascular leakage or impaired filtration.