Endothelial cells

The endothelial cells account for 20% of total liver cells, but for only 3.3% of the protein content of the liver. They possess slender extended processes containing pores (fenestrae) that are arranged in so-called sieve plates. Are christmas cactus poisonous to cats or dogs https://cactus-christian.org/cactus-poisonous.html.

These fenestrae constitute only 6–8% of the surface area of the endothelial lining, so that the endothelium is thought to act as a selective barrier between the blood and the parenchyma. The size of fenestrae is dynamic and can be modified by both physical and chemical forces, which are actively controlled by the actin-containing components of the cytoskeleton, particularly microtubules.

The surface of the sinusoidal endothelial cells are relatively smooth compared with those of Kupffer cells, and generally are lacking in filopodia or lamellipodia. They possess numerous bristle-coated membrane invaginations and vesicles and many other lysosome-like vacuoles, which correlate with the high degree of endocytotic activity present in these cells.

Unlike cells of the vascular endothelium, liver endothelial cells lack an underlying basement membrane so that solutes and small particles have access to the perisinusoidal space. However, scattered connective tissue elements and extracellular matrix material are associated with the abluminal surfaces of the endothelial cells.

The endothelial cells can secret a wide variety of proteins, such as interleukins, interferon, and TNF-α. Thus, along with Kupffer cells, the endothelium participates in host defense mechanisms in the liver.