Structure and Function of the Blood-Brain Barrier

The cerebral endothelial cells of the blood-brain barrier originate from the middle germinal sheet of the embryo, the mesoderm [17]. Concomitant with migration and proliferation of capillary endothelial cells during formation of the cerebral vascular network occurs the imprinting of the cells. Thereby, induction by the cellular surrounding plays an important role [18-21], The relevance of the cellular environment for the development of the barrier function of cerebral microvessels was first demonstrated by Stewart and Wiley [22], who transplanted embryonic brain tissue of a quail into embryonic gut tissue of chicken and vice versa. The cerebral transplant was vascularized by intestinal vessels, in which properties of the blood-brain barrier had been induced. In transplanted brain vessels, however, no characteristics of a barrier could be demonstrated, due to the lack of a neuronal environment. These results indicated that the cerebral microvessels are of extraneuronal origin, with properties that are induced by the cellular environment. In addition, brain tissue has the capability to induce blood-brain barrier characteristics also in noncerebral vascular tissue [23], 

The density of cerebral capillaries, especially in the cortical grey matter, is very high with mean distances of 40 /xm. The capillary network has a total length of 600-650 km, the mean velocity of the blood flow is below 0.1 cm/s, and the luminal surface extends to 15-30 m2. Thus the blood-brain barrier represents an important surface for potential drug delivery besides gut (30CM100 m2), lung (70-120 m2), or skin (1.8 m2) [24-26, 33-37], 

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Chapter 27 Structure and Function of the Blood-Brain Barrier.575... 

Describe the structure and function of the blood-brain barrier... 

Rapoport, S. I. Structure and function of the blood-brain barrier, in Cerebral Metabolism and Neural Functions (eds.) Passomeau, J. V., Hawkins, R. A., Lust, W. D., p. 96, Baltimore, Williams and Wilkins 1980... 

Begley DJ, 2007. Structure and function of the blood-brain barrier. In Touitou E, Barry BW (eds) Enhancement in Drug Delivery. CRC Press. Boca Raton, FL. p. 575. 

The blood-brain barrier forms the interface between the bloodstream and the brain parenchyma and thus controls the passage of endogenous substances and xenobiotics into and out of the central nervous system. Brain microvessels exhibit a variety of unique structural features, such as an extremely tight endothelium without fenestration, a very low rate of pinocytosis, tight junctions between endothelial cells excluding paracellular permeability, and a series of polarized transport proteins. The following chapter describes the structural and functional characteristics of the blood-brain barrier with emphasis on transport proteins, as well as in vitro techniques, which allow studying this complex barrier in the brain. 

Biochemically lead binds to sulfhydryl (-SH) groups in proteins, that is, it can inhibit enzymes and affect the structures and functions of structural proteins. Some of the effects of this binding include increased permeability of the blood-brain-barrier, breakdown of vascular tissue, destruction of the ground substance in cells leading to conditions of anemia and kidney damage. 

The significance of the barrier function of membranes has been the topic of considerable research. The blood-brain barrier and the blood-retinal barrier are well understood, and the microscopic structures imparting and controlling barrier properties have been quite thoroughly investigated and the science reviewed [15, 154-155], The structures and functions of ocular membranes specific to transport associated with ophthalmic drug administration also have been topics of extensive research [15, 157-158],... 

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