Aiims November 2010 – MCQ 1

Which of the following is not permeable through the blood brain barrier?
A. Water
B. Lipophilic drugs
C. Gas
D. Proteins

Correct answer : Proteins

Blood brain barrier is freely permeable to water, gases like oxygen and carbondioxide and lipid soluble substances. It is slightly permeable to ions like sodium, potassium and chloride. It is impermeable to plasma proteins, and large organic molecules that are not lipid soluble.