Biological barrier

A biological barrier is a natural selectively permeable membrane that protects certain organs or tissues by allowing some substances to pass through them, and blocking entry of other substances.

It can refer to:


 * Blood-brain barrier, a biological barrier that prevents entry of harmful substances into the brain by selectively allowing some substances to pass through it
 * Blood-testis barrier, the biological barrier between blood and testes
 * Blood-placental barrier, the biological barrier between a pregnant individual's blood and foetal blood (blood of one or more foetuses)
 * Blood-CSF barrier, the biological barrier between blood and cerebrospinal fluid (CSF; also called brain fluid)
 * Blood–spinal cord barrier, the biological barrier between blood and the spinal cord
 * Blood–saliva barrier, the biological barrier between blood and saliva