BLOOD-BRAIN BARRIER

 

INTRODUCTION:  The blood–brain barrier (BBB) is a highly selective permeability barrier that separates the circulating blood from the brain extracellular fluid in the central nervous system (CNS).  The blood–brain barrier is formed by brain endothelial cells, which are connected by tight junctions with an extremely high electrical resistivity.

SELECTIVITY OF THE MEMBRANE:  The blood–brain barrier allows the passage of water, some gases, and lipid soluble molecules by passive diffusion, as well as the selective transport of molecules such as glucose and amino acids that are crucial to neural function.  On the other hand, the blood–brain barrier may prevent the entry of lipophilic, potential neurotoxins by way of an active transport mechanism mediated by P-glycoprotein.

CELLULAR ACTECTURE OF THE BBB:  Astrocytes are necessary to create the blood–brain barrier. A small number of regions in the brain, including the circumventricular organs (CVOs), do not have a blood–brain barrier.  The blood–brain barrier occurs along all capillaries and consists of tight junctions around the capillaries that do not exist in normal circulation.  Endothelial cells restrict the diffusion of microscopic objects such as bacteria and large or hydrophilic molecules into the cerebrospinal fluid (CSF), while allowing the diffusion of small or hydrophobic molecules including O₂, CO₂, hormones).  Cells of the barrier actively transport metabolic products such as glucose across the barrier with specific proteins. This barrier also includes a thick basement membrane and astrocytic end feet.

RELATED;

1.  IMPULSE PROPAGATION IN THE CNS

2.  METABOLIC PROFILE OF THE BRAIN

3.  ANATOMY AND PHYSIOLOGY

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