Question

1. Explain the issues or barriers that must be considered for a drug to pass through the gastrointestinal tract, be absorbed into the bloodstream, and ultimately arrive at the brain.

Answer 1

The capillary endothelial cells in brain have tight junctions and lack large intracellular pores. An investment of neural tissue covers the capillaries ,and together they constitute the so called blood brain barrier.A blood brain barrier located in the choroid plexus , capillaries are lined by choroidal epithelial having tight junctions.These barrier are lipoidal and limit the entry of nonlipid soluble drugs that is streptomycin .Only lipid soluble are able to penetrate and have action on the central nervous system.

The blood brain barrier is deficient in the medulla oblongata and at certain periventricular sites.Exit of drugs from the brain is not dependent on lipid solubility and is rather unrestricted. efflux transporters like anion transporter present in the brain and choroidal vessels extrude many drugs that enter brain by other processes .Some of drugs accumulate in the brain by utilizing the transporters for endogenous substances.