The Blood-Brain Barrier (BBB)
the BBB contains tight junctions. What are tight junctions?
intercellular junctions that are tight and don't freely allow diffusion
why is the modification of a drug of concern to physicians and pharmacists?
it can alter the drugs activities and physical properties
blood-brain barrier
semipermeable system that prevents some chemicals from passing from the blood stream to the brain
what is the principal energy source for brain cells?
glucose
what are the main functions of the blood brain barrier?
-help provide neurons with their exact nutritional requirement (glucose) -maintain the proper ion balance within the brain -isolate the brain from certain chemicals
name three methods pharmacist used to make drugs acceptable to the BBB:
-making it more soluble into lipids rather than water -make it look like natural substances that are actively transported through the BBB -inject highly concentrated sugar solutions into the arteries that supply the brain with blood so that the endothelial cells shrink to allow the drugs to diffuse
how is your blood glucose levels maintained?
A hormonal system including the hormones insulin and glucagon
what is the composition of the blood brain barrier?
A single layer of tile like endothelial cells that line the inner surface of capillaries in the brain; outside of the brain, the capillaries have large gaps but inside the brain they are tightly packed
of all the drugs prescribed and taken, how many actually into the brain?
A small amount
where does a second barrier similar to the BBB exist?
behind the retina
What is the main factor that determines whether a drug can pass the BBB? Why?
solubility in water and in lipids; cell membranes are composed partially from lipids so substances dissolved into lipids can pass through the membrane while substances that are dissolved in water cannot pass through the membrane because the lipids are hydrophobic
when does the BBB present a problem to physicians who are trying to treat a patient who is seriously ill and why?
when the disorders to be treated involve the brain and brain functions because the drugs are stopped by the blood brain barrier and cannot effectively treat it
