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Fenestrated Capillaries

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These capillaries are permeable to items smaller than albumin.

Tunica Externa

Absent

Tunica Media

Absent

Tunica Interna (Intimia)

Fenestrated capillaries have permeability intermediate to that of sinusoidal and continuous capillaries. The intercellular clefts (spaces between cells) are not large enough to allow the movement of red or white blood cells. However, they are large enough to allow the movement of proteins.  Albumin, an important protein contributing to the colloid osmotic pressure of blood plasma is just a smidge larger than these fenestrations (a word which means “window.”  This type of capillary is incredibly important in the process of filtration in the kidney.  Fenestrated capillaries called glomeruli allow items smaller than albumin to escape to the filtrate. This filtrate is unadjusted urine. However, these capillaries prevent albumin and larger substances from escaping the blood.

Lumen

Big enough for only one erythrocyte

Micrograph of kidney glomerulus (Slide 205) with fenestrated capillaries. Tissue stained with hematoxylin and eosin (H&E). Round glomeruli show clusters of red-stained cells and blue nuclei. Surrounding tissue includes tubules and capillaries, also stained with red and blue. A large red area covers the lower right portion of the slide.
Figure 1: Kidney glomerulus capillaries, stained tissue sample.

Figure 1: Kidney, monkey, vascular injection of red gelatin, counterstained with hematoxylin, 20X Slide 205-1
All by University of Michigan Histology, licensed under CC BY-NC-SA 3.0.

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Arterioles
Sinusoidal Capillaries
Fenestrated Capillaries
Continuous Capillaries
Venules
Veins

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