The blood-brain barrier and blood-gonadal barrier protect the brain, neurons, ovaries, and testes due to their critical importance and limited regenerative capacity.

“The blood-brain barrier or BBB is a barrier. It's a wall around the brain and you have this barrier because the brain is so important. It has this feature that the neurons there don't recreate themselves after injury, like other organs of the body. There's not a lot of turnover of cells despite what you might've heard. And so nature has created this BBB, this blood brain barrier to make sure that certain molecules in particular, large molecules don't get across the blood-brain barrier. 'Cause it can be damaging to those tissues. Incidentally, you also have a very rigid or stringent barrier around other organs, which are the gonads. So the ovaries and the testes and the brain are the organs of the body that nature has gone out of its way to protect, give this additional layer of the blood-brain barrier or as you might imagine for the testes and the ovaries, it's going to be the blood gonadal barrier.”