Sinusoid (blood vessel)
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A sinusoid is a small blood vessel similar to a capillary but with a fenestrated endothelium.
Sinusoids are found in the liver, lymphoid tissue, endocrine organs, and hematopoietic organs such as the bone marrow and the spleen. Sinusoids found within terminal villi of the placenta are not comparable to these; they possess a continuous endothelium and complete basal lamina.
Sinusoids are highly permeable, having larger inter-cellular clefts, fewer tight junctions, and fenestrated endothelial cells. The level of permeability is such as to allow small and medium-sized proteins such as albumin to enter and leave the blood stream. The sinusoids of the liver are of particular importance to the function of that organ, and are discussed in more detail at liver sinusoid.
Fenestrations
In sinusoid blood vessels, fenestrations are gaps in between the endothelial cells, increasing permeability.
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