Blood-brain barrier cellular structure

Lossinsky AS, Shivers RR. Structural pathways for macromolecular and cellular transport across the blood-brain barrier during inflammatory conditions. Review. Histol Histopathol 2004 19(2) 535-64. 

The net result of these turnover studies is to show that lipids in brain are a part of the dynamic biochemistry of the body — even though they may function primarily as structural components. These data strongly suggest that considerable caution must be exerted in the interpretation of isotopic experiments conducted in vivo, especially when complex compounds are being studied. It emphasizes the need to know more than the radioactivity in the lipid. Other perimeters, such as pool sizes, turnover rates of the pools themselves, permeability, cellular barriers (such as the blood-brain barrier) and other related factors must be determined before a full explanation of the isotope data can be made. 

The tissues discussed above are examples of cellular permeability, but capillary permeability must now be discussed. The capillaries of the blood-system, like those of the kidney glomerulus (see below), have porous Type 4 membranes and allow the passage of ions and proteins. However the capillaries of the brain are differently structured see blood-brain barrier, in the following. 

The basement membrane provides a structural barrier to extravasation of cellular blood elements and anchors endothelial cells to astrocytes. In BBB it contains extracellular matrix (ECM) molecules, such as laminin, type IV collagen, and fibronectin. Most of these are substrates for a family of neutral proteases called MMPs, especially MMP-2 and MMP-9. More than twenty MMPs and four of their TIMPs act together to control tighdy temporally restricted, focal proteolysis of ECM. They are also implicated in opening the BBB, and increased MMP production may injure the BBB, at least in part through their proteolytic activity at the tight junctions of brain endothelial cells and the BBB basal lamina. 

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