Which of the following statements best explains why several drugs cannot enter easily
the central nervous system?
A. Epithelial cells of choroid plexus have no active transport systems B. The protein content of cerebrospinal is much lower than that of plasma C. The pH of cerebrospinal fluid is lower than that of plasma D. Endothelial cells of brain capillaries and choroid plexus have tight junctions E. There are no lymphatic vessels in the brain
Endothelial cells of brain capillaries and choroid plexus have tight junctions-1) learning objective: explain how the blood-brain barrier can affect the drug distribution intothe central nervous systemanswer: ddrugs may enter the cns by crossing the cerebral capillaries (i.e. from plasma to theextracellular fluid) or by crossing the choroid plexus (i.e from plasma to the cerebrospinal fluid).the composition of csf is essentially the same as that of brain ecf and there appears to befree communication between the brain ecf and csf. in both the above mentioned cases thedrug must cross the blood brain barrier. one reason why this barrier limits the transfer of druginto the central nervous system is because endothelial cells of brain capillaries are connectedone to another by occluding zonulae and do not have fenestrae.a) actually the cell of choroid plexus have several transport systems that can carry drugs in andout the cerebrospinal fluid.b, c, e) all these statements are correct but they are not the reason of the poor entry of somedrugs into the cns.