Did you know the brain has a defensive system?
The brain needs oxygen, nutrients, and food, all of which come from the blood supply. However, the brain’s neurons are sensitive to many chemicals that can be contained in blood. To solve this problem, God designed a blood-brain barrier.
Brain capillaries are different than ones from the body, and they act as a semi-permeable barrier. They block harmful substances such as bacteria from entering the brain, but allow the passage of essential nutrients. The cells that line these capillaries have a special chemical process that figures out what nutrients the brain needs, and then actively transports those nutrients.
God knew our brain cells were sensitive and needed protection; we can praise Him for creating a blood-brain barrier!
(Source: Brighthub.com science genetics articles)