The Human Brain : From Neurone to Nervous System

BLOOD-BRAIN BARRIER


  1. When some dyes, such as trypan blue are injected into the blood, they colour many tissues in the body but do not enter the CNS. Lipid soluble molecules tend to enter the brain whereas hydrophilic molecules do not.

  2. The blood brain barrier however is more than a passive barrier. Brain capillaries contain tight junctions between the endothelial cells, and are surrounded by the end feet of astrocytes that touch capillaries and neuronal cell bodies.

  3. Astrocytes are concerned with the nutrition of neurones, the metabolism of neurotransmitters, and causing vasodilatation in active regions of the brain.

  4. Circumventricular Organs occur in areas where the barrier between CSF and neurones is deficient. These areas occur where molecules need to cross the barrier: in the neurohypophysis (involved in neurosecretion), and in chemosensitive areas where neurones taste the composition of the blood or CSF (e.g., for hormones or osmolality), or in the case of the area postrema, for substances that initate vomiting.

  5. Some other specialised fluid compartments within the CNS contain fluids with unique compositions.



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