Blood-Brain Barrier

Overview

Snapshot

• A 56-year-old female is brought to the emergency department by her daughter due to new-onset abnormal movements suggestive of a seizure. While the patient is being managed, the physician learns that the patient is being treated for lung cancer. Head CT was obtained after the patient was stabilized.

Introduction

• Structure 
  • tight junctions between nonfenestrated capillary endothelial cells
    • also consists of astrocytic foot processes, pericytes, basement membrane
  • irradiation, malignancy, infection can disrupt the blood-brain barrier (BBB)
    • infarction destroys tight junctions → vasogenic edema
      • fluid is extravasated into the interstitial space
• Function
  • control entry of substances into the brain
    • substances cross via diffusion, ion channels, and selective transport proteins
      • diffusion: nonpolar/lipid-soluble substances readily cross the BBB
        • O2, CO2, heroin, nicotine
      • ion channels: movement of Na⁺ and K⁺
      • selective transport proteins: nutrients
        • glucose, amino acids, peptides
        • removes metabolites
  • certain areas of the CNS lack a BBB
    • posterior pituitary (neurohypophysis)
      • allows ADH release from brain into systemic circulation
    • area postrema
      • chemotherapeutic drugs → vomiting
    • organum vasculosum lamina terminalis (OVLT)
      • senses blood osmolality