Anatomy and physiology of the blood-brain barrier

Abstract

Essential requisite for the preservation of normal brain activity is to maintain a narrow and stable homeostatic control in the neuronal environment of the CNS. Blood flow alterations and altered vessel permeability are considered key determinants in the pathophysiology of brain injuries. We will review the present-day literature on the anatomy, development and physiological mechanisms of the blood-brain barrier, a distinctive and tightly regulated interface between the CNS and the peripheral circulation, playing a crucial role in the maintenance of the strict environment required for normal brain function.

Keywords: Blood–brain barrier; Neuroglia; Neurovascular unit; Vessel permeability.

Figure 1. Potential routes for infiltration and transport across the endothelial cells forming the BBB

Cells may cross the BBB through or adjacent to the tight junctions. Solutes may passively diffuse through the cell membrane. Active efflux carriers may pump some of these passively penetrating solutes out of the endothelial cell. Carrier-mediated influx (passive or secondarily active) can transport essential polar molecules, such as amino acids, glucose and nucleosides into the CNS. Receptor-mediated transcytosis (RMT) can transport macromolecules such as peptides and proteins across the endothelium. Adsorptive-mediated transcytosis (AMT) is induced non-specifically by positively charged macromolecules and can result in passage across the BBB. Tight junction modulation may occur, affecting the permeability of the paracellular aqueous diffusional pathway.