Circumventricular Organs (System) have been well studied, starting with Paul Ehrlich work with Trypan Blue in 1882, and research on their functions is still going on. However, Neuroscience medical students find it difficult to understand them. This short PPTX is meant to succinctly explain the Circumventricular Organs. Short Video clips pertaining to each CV Organ on a human brain specimen, created and uploaded on YouTube by the author, Dr Sanjoy Sanyal, Professor and Course Director of Neuroscience, are embedded between slides, to provide a narrative highlight to what is mentioned in the slides. Tags: Median Eminence, Tuber Cinereum, Arcuate Nucleus, Organum Vasculosum, Lamina Terminalis, Subfornical Organ, Pineal, Epiphysea, Subcommissural Organ, Area Postrema, Supraoptic Nucleus, Suprachiasmatic nucleus, Preoptic nucleus "Copyright Disclaimer Under Section 107 of the Copyright Act 1976, allowance is made for "fair use" for purposes such as criticism, comment, news reporting, teaching, scholarship, and research. Fair use is a use permitted by copyright statute that might otherwise be infringing. Non-profit, educational or personal use tips the balance in favor of fair use."

1. Dr Sanjoy Sanyal MBBS, MS (Surgery), MSc
(Royal College of Surgeons of Edinburgh),
ADPHA
Professor and Course Director of
Neuroscience – FCM-III Neurology

2. Paul Ehrlich (1882)
After IV injection of Trypan
Blue, most Brain areas did not get stained
These areas are inside the BBB
Some areas of Brain did get stained
These structures are outside the BBB; i.e.
they do not have a BBB

3. Tight Junctions (Claudin /
Occludin) between
Endothelial Cells
They form a continuous
Lipid Bi-layer
Continuous Basement
Membrane outside
Astrocyte Podocytes
form complete circle
Red arrows
indicate lack of
permeability

4. Highly Vascularized
Fenestrations of
Endothelial Cells
Permeable Basement
Membrane
Astrocyte Podocytes
do not form complete
circle
Red arrows indicate
permeability
Exception: Sub-
Commissural
Organ has Non-
fenestrated
Capillaries

5. Tancytes line the Floor
of 3rd Ventricle
Body of Tancyte is in
contact with CSF
Multiple Foot-Process
extend towards
adjacent Capillary
Provides conduit
between CSF and Blood
Tancytes play
important role in
certain Non-BBB
areas

6.  Most Non-BBB areas
are around 3rd
Ventricle, and one in
4th Ventricle
 They are called
Circumventricular
Organs
 They are bathed by
CSF and are also in
contact with
Capillaries
 Median Eminence of
Tuber Cinereum
 Organum Vasculosum of
Lamina Terminalis
 Sub-Fornical Organ
 Pineal Gland
 Sub-Commissural Organ
 Area Postrema
 Wall of Optic Recess
 Posterior Lobe of Pituitary

7. Chemosensitive Organs
Allow ‘sampling’ of Blood
Endocrine Feedback and Regulation
Homeostasis
Metabolic Regulation
Fluid Electrolyte Balance
Detect Toxins in Blood
CSF Circulation(?)

8. Tancytes line the Floor of
3rd Ventricle and ME-TC
Has Arcuate Nucleus that
detects Endocrine
Feedback to Hypothalamus
via the Tancytes
Releases RH/IH, P-IH, and
maintains Basal Levels of
Hormones (FSH-LH)
In Floor of 3rd Ventricle:
Raised Central Part of a
Convex gray matter in
the Ventral-most part of
Hypothalamus #1

9. Has Osmoreceptors
Regulates ADH release
by Supraoptic Nucleus
Provides Vascular
Outlet for LH-RH by Pre-
optic and GH-IH by
Suprachiasmatic (Both
are adjacent to LT)
A.k.a. Vascular
Organ of Lamina
Terminalis #2

10. On inferior surface of
Fornix, at level of
Foramen of Monroe (#3)
Angiotensin II Receptors
Neurons from SFO project
to SO Nucleus and OV-LT
(Both are Osmoreceptors)
Fluid Electrolyte balance

11. Pinealocytes
(Epiphyseal Cells) #4
Highly Vascular
Fenestrated Capillary
Release Melatonin into
3rd Ventricle
Transported by
Tancytes in Floor of 3rd
Ventricle
Act on Pituitary Gland

12. Special Epithelial / Glial
Cells
Non-fenestrated
Capillaries
Functions: (a) Circulation
of CSF (Hydrocephalus);
(b) Clearance of certain
compounds (?)
Below Posterior
Commissure #5
At 3rd Ventricle–
Aqueduct of
Sylvius Junction

13.  Modified Astrocyte-like
Neurons
 Fenestrated Capillaries
 5-HT3 Receptors
(Excitatory Ionotropic)
 Induces Vomiting from
Morphine, Blood 5-HT
 Gets Afferents from CTZ
and GIT
 Plays Role in Food
Intake / CVS Control
 In Floor of 4th
Ventricle, Between
Vagal Triangle and
Inferolateral margin
of Rhomboid
Fossa, just Rostral to