Page 174 - The Miracle in the Cell Membrane

The Miracle in the Cell Membrane

ids and solutes through the cell mem brane. In cells out side
the brain, how e ver, these sacs are wide spread.

The impor tance of the bar ri er
We can bet ter under stand the impor tance of the
blood-brain bar ri er from dis eas es that occur in that bar ri -
er's absence. Tumors, brain-tis sue defects and edema—
swell ings due to the accu mu la tion of flu ids and pro -
teins—cause this bar ri er to col lapse. Since fewer sacs
form in the walls of the endo the li um cells, leak age
begins, or the tight bonds between the cells are loos ened.
Damage to the bar ri er leads to the accu mu la tion of
fluid and lead poi son ing in brain tis sue. The metal first
enters the endo the li um cells and then the astro cytes.
After the lead has dam aged the bar ri er, the brain is more
vul ner a ble to other sub stan ces.
The blood-brain bar ri er is no longer con sid ered a pas -
sive struc ture, but a dynam ic inter face between the blood
and the brain. Yet our under stand ing of its main te nance
and trans port mech a nisms is still incom plete. 54
Every por tion of our bod ies has been spe cial ly cre at -
ed for life. These parts, only a few of which we shall look
at in this book, have occu pied sci en tists for dec ades and
con tain mech a nisms that astound inves ti ga tors. Why is
this blood-brain bar ri er in exact ly the right place only
and not among cells in any other part of the body? How
do the cells know that the brain needs a sta ble envi ron -
ment, and so entry to and exit from its cells must be more
tight ly con trolled? No doubt the cells them selves do not

172