So now, let's talk about the blood flow to the brain.
The blood flows to the brain by way of the vertebral and carotid arteries.
It flows away from the brain and back to the heart by way of the jugular veins.
The brain utilizes about 20% of the body's oxygen and glucose supply.
Unlike other parts of the body, the neural cells are unable to undergo lactic acid fermentation
so they have an absolute requirement for both glucose and oxygen in order to have energy.
Any interruption of the oxygen supply to the brain can result in weakening
and if that interruption is too long, it can also result in permanent damage
or even death of the brain cells.
As well because the brain cells must undergo cellular respiration for energy,
glucose is also essential.
A glucose deficiency may produce mental confusion,
dizziness, convulsions, and unconsciousness.
This is especially important in patients that may be diabetic
as they have to be very aware that they have an adequate amount of glucose for brain activity.
So when we refer to the blood that is flowing to the brain,
it's important to note that there is a barrier between the blood and the brain cells.
This barrier is known as the blood-brain barrier or the BBB.
The blood-brain barrier protects the brain cells from harmful substances
and pathogens by acting as a selective barrier
and preventing the passage of many other substances
that are found in the blood into the brain.
Lipid-soluble substances like oxygen, carbon dioxide, steroid hormones, alcohol,
and nicotine can pass readily through this barrier.
However, molecules like proteins and antibiotics are not able to pass at all.
Water and glucose which are very important for brain activity
can pass by way of facilitated diffusion.
The blood-brain barrier is established by creating tight junctions
with the endothelial cells of the blood capillaries that go to the brain.
The blood-brain barrier can also prevent good things from getting into the brain.
The blood-brain barrier can prevent entry of therapeutic drugs and so it is important
when designing drugs that need to go to the brain to take the blood-brain barrier into account.
Entry to the brain can also cause a breakdown of this blood-brain barrier.
If this occurs, this may permit passage of substances
that normally would not be able to get into the brain tissue.