Answer to Question 1
The cells comprising the capillaries that provide blood to the brain are tightly packed together, with minimal pores between them. In addition, parts of glial cells may cover the outside of the capillaries. These comprise a lipid barrier through which non-lipid soluble drugs cannot pass, unless the molecules are compatible with transport proteins that can carry them across these membranes. Thus, in order to penetrate this barrier, the molecule must be small and nonionized, e.g., like alcohol or lipid soluble or possess a structure allowing it to bind to a transport protein to be carried across these lipid membranes.
Answer to Question 2
The fetus has greater blood flow to brain than in the mother, has a poorly developed bloodbrain barrier, has poorly developed P450 enzyme system to metabolize drugs, and poorly developed kidney system for eliminating drugs from the body
brain connections
Anatomical Subdivisions of the Brain
A Midsagittal View of the Brain and Part of the Spinal Cord
Pathways of the Visual System in the Brain
Drug development time line.
Sagittal section through brain and spinal cord