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Renin Angiotensin Mechanism.

Blood Brain Barrier (BBB).

 

Blood Brain Barrier (BBB).:

  • The term blood-brain barrier denotes the barrier separating the brain tissues from the blood circulation. 

  • The structural basis consists of three parts:

    • Layer of endothelial- cells :interconnected through tight junctions and not containing fenestrations (Gaps).

    • Basal membrane : consisting of basal lamina of astrocytes and basal lamina of endothelial cells.

    • Protrusions of astrocytes : so called pedicles, which packs on the basal membrane.

  • Structure:

  • The BBB is:

    • High permeability for: water, carbon dioxide, oxygen, most lipid-soluble substances (e.g.: alcohol and anesthetics)

    • Little permeability for: electrolytes (e.g.: Na+, Cl-, K+)

    • Almost totally impermeable to: plasma proteins and most non-lipid-soluble large organic molecules.

  • Some small CNS regions are out of the BBB:

    • Area postrema of the fourth ventricle.

    • Subfornical organ.

    • Epiphysis.

    • Neurohypophysis.

  • Functions of the BBB

    • Protection of the nervous system from pathogens.

    • Precise local environment regulation.

    • Retaining of certain factors within the brain (neurotransmitters, neuromodulators).

Commonly asked question.

  1. Write a short note on Blood Brain Barrier (BBB).
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