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Blood-brain barrier & circumventricular organs
German physician Paul Ehrlich (1854-1915)
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Paul Ehrlich (1882)
After IV injection of trypan blue, most brain areas did not get stained
- these areas are inside BBB
Some areas of brain get stained.
- these areas do not have BBB
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Function
Neurons are like ladies. They are very sensitive.
So, the function of BBB is like a mother:
STABILIZE when they become sad
PROTECTS from the toxins of the world
HOLD YOU to maintain the concentrations
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BBB is formed by “BBB”
Binding tight junctions
Basement membrane
Base-foot astrocyte
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Capillary
Have 3 types of capillaries in the body  CSF
Continuous – CNS, muscle, endoneuro, peripheral nerve
Sinusoidal – liver, spleen
Fenestrated – glomerulus
In the CNS, you have Continuous capillaries
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Pass
Have 3 types of transport in the body PTT
- Paracellular
- Transcellular
- Transcytotic-vesicular
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In the BBB
- No paracellular due to tight junctions
- poor transcellular and transcytotic-vesicular
You have guards in the CNS – P-glycoproteins
- take lipid soluble substances out the brain
- energy-dependent transport
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What does not pass BBB?
BIG guys – plasma proteins & substances attached to them
HORNY guys – highly charged
TOXIC guys – even if small
What does pass BBB?
BABY molecules – H2O, O2, CO2
- But, H+ no, He is a Horny guy
SWETTY guys – glucose & aminoacids (carrier mediated)
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BBB vs BCF difference
Where is the tight junction is the ≠
BBB – Blood (endothelial)
vs
BCB – Choroidal (choroidal epithelial cells)
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Types of cerebral edema
COVI: Cytotoxic, Osmotic, Vasogenic, Interstitial
- vasogenic is considered the MC
- doesn’t have a clear mechanism, may be a combination of mechanisms
Types
Intracellular – cytotoxic & osmotic
Extracellular – vasogenic
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Circumventricular organs
- circumventricular organs are specialized areas of CNS where BBB is modified or broken
- all of them are surrounded by 3rd & 4th ventricles
- ependymal cells proximal to ventricular areas are modified and their name are tanycyte
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Micro-structure
- highly vascularized
- fenestration of endothelial cells
- permeable basement membrane
- astrocyte podocyte (foot processes) do not form complete circle
EXCEPTION: subcommissural organ has non-fenestrated capillaries
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Tanycyte
- line the floor of the 3rd ventricle
- conduit between CSF and blood
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Function of circumventricular organs
- chemosensitive organs
- allow “sampling” of blood
- endocrine feedback and regulation
- homeostasis
- metabolic regulation
- fluid electrolyte balance
- detect toxins in blood
- CSF circulation
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“POSSMAN”
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Pineal gland
- melatonin
youtu.be
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OVLT (organ vasculosum of lamina terminalis)
Receptors: ATII; IL-1; osmoreceptors
It is where the location of the anterior neuropore. If not closes, you will have anencephaly.
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