Clinical Importance of Alterations in Barrier

Abstract

The blood–brain barrier (bbb) includes all structures between the capillary lumen and the central nervous tissue: the endothelium of the capillaries, the basement membrane, and the surrounding glial foot processes. Functionally, the bbb should be regarded as a system limiting the free exchange between blood and brain; it further exerts its function on transport processes essential for the nutrition of the brain and on those in the opposite direction, from the brain into the blood. The bbb is also effective as an intermediate system in humoral regulations of peripheral vegetative functions. Alterations of the bbb with increased permeability cause enhanced exchange between blood and brain which is dependent on the intensity of the disturbance; by this means the penetration of viruses and bacteria from the blood into the brain may be facilitated. This increased permeability may be followed by cerebral edema and by an increased predisposition for epileptic seizures. This paper demonstrates the increased permeability of the bbb in pathological conditions, that is, pathological conditions involving a reduced exchange between blood and brain. Under normal conditions glucose is the most important if not the only source of energy for the brain. Because glucose cannot enter the brain from the blood by a process of diffusion, glucose uptake is independent of the glucose level of the blood, over a wide range. The nutrition of the brain depends on a transport mechanism specific for glucose in the bbb system. As a conclusion, results of measurements of cerebral metabolism in patients with mental disturbances and in older men without great mental disturbance have also been mentioned.