Thrombomodulin I is produced by all of the following EXCEPT (AIPG 2008)
a.The endothelium of the blood vessels also plays an active role in preventing the extension of clots into blood vessels. All endothelial cells except those in the cerebral microcirculation produce thrombomodulin, a thrombin-binding protein, and express it on their surface. In the circulating blood, thrombin is a procoagulant that activates factors V and VIII, but when it binds to thrombomodulin, it becomes an anticoagulant in that the thrombomodulin – thrombin complex activates protein C. Activated protein C (APC),along with its cofactor protein S, inactivates factors V and VIII and inactivates an inhibitors of tissue plasminogen activator, increasing the formation of plasmin.
b.Endothelial cells are wide and thin, tile-like and slightly curved to fit the curvature of the vessel.
c.They are somewhat elongated in the direction of blood flow, especially in arteries.
d.Endothelial cells firmly adhere to each other at their edges, so that the lining of the lumen presents no discontinuity (except in sinusoids).
e.The thickness of endothelial cells is maximal at the level of their nucleus, where it can reach 2 –3 mm, this part of the cell often bulging slightly into the lumen.
f.Elsewhere, the endothelial cell is thinner and laminar; in capillaries, these portions of the cell are very attenuated, often measuring as little as 0.2 mm in thickness.
g.The luminal surface of the endothelium is relatively smooth.
h.However, it is common to find endothelial laminar projections into the lumen, especially near the cell junctions.
i.The cell surface is pitted by the numerous caveolae and the membrane is coated by a prominent glycocalyx.
j.The glycocalyx is a highly-charged, polysaccharide-rich felt of glycoproteins, anchored to the cell membrane, which controls the transport of solutes and may mediate the mechanical effects of blood flow on the endothelial cells.
k.Because of the high charge density the glycocalyx may contribute to the non-thrombogenic properties of the surface of the intact endothelium.
l.The glycocalyx is not seen in standard electron micrographs of the endothelium, but can be visualized with electron-dense substances, such as ruthenium red, which bind specifically to glycoproteins.
m.The abluminal surface is also pitted by caveolae and it rests over a basal lamina.