Ventricular system

1. VENTRICULAR SYSTEM,
CEREBROSPINAL FLUID,
BLOOD-BRAIN BARRIER, AND
BLOOD-CEREBROSPINAL FLUID BARRIER
Charlie A. Clarion, MD
Diplomate in Internal Medicine
June 11, 2018

2. Reference

3. Disclosure
• I am not affiliated
to or funded by any
pharmaceutical
company.

4. Objectives
• At the end of this lecture, medical
students are able to:
• 1. learn the locations, the functions,
the origins, and the fate of the
cerebrospinal fluid;
• 2. understand the structure and
functions of the blood-brain and
blood-cerebrospinal fluid barrier; and
• 3. learn how certain parts of the brain
are protected from potentially toxic
drugs or other exogenous substances

5. VENTRICULAR SYSTEM

6. Ventricles
• 4 fluid-filled cavities
the hold CSF

7. Lateral Ventricles
• C shaped cavity
• 2 large lateral
ventricles, one in
each cerebral
hemisphere

8. Lateral Ventricles
• Interventricular
Foramina (of
Monro) –
communication
between lateral
ventricles and third
ventricle

9. Lateral Ventricles
• 3 horns and 1 central
part/body
– Anterior horn: frontal
lobe
– Posterior horn:
occipital lobe
– Inferior horn: temporal
lobe
– Central part/body:
parietal lobe

10. Third Ventricle
• Slitlike cleft between
the two thalami
• Communicates :
– Anteriorly with
lateraL ventricles
through
interventricular
foramina (of Monro)
– Posteriorly with
fourth ventricle
through cerebral
aqueduct (of Sylvius)

11. Cerebral Aqueduct (of Sylvius)
• Narrow channel
• Around ¾ inch (1.8
cm) long
• No choroid plexus in
the cerebral
aqueduct (of Sylvius)

12. Fourth Ventricle
• Situated anterior to
the cerebellum and
posterior to the
pons and the
superior half of the
medulla

13. Fourth Ventricle
• Communicates with
subarachnoid space
through:
– Single median
opening: Foramen of
Magendie
– Two lateral
apertures: Foramina
of Luschka

14. Choroid Plexuses
• Produce CSF
• Location:
– Lateral ventricles: lateral edge of tela choroidea
between the fornix and upper surface of the
thalamus
– Third ventricle: tela choroidea situated above the
roof of the ventricle
– Fourth ventricle: tela choroidea projecting
through the roof of the ventricle

15. Central Canal
• Communicates
– Superiorly to the
fourth ventricle
– Inferiorly to the
inferior half of the
medulla oblongata
and through the
entire length of the
spinal cord

16. Subarachnoid Space
• Space filled with CSF and contains large blood
vessels of the brain

17. CEREBROSPINAL FLUID

18. Characteristics and Composition
• Site: Ventricles of the brain, subarachnoid space
• Volume: 150 cc
• Pressure: 60 – 150 mm H2O
• Characteristics: clear, colorless fluid, with
inorganic salts similar to those in plasma, trace
protein
• Glucose content: half of plasma
• Few lymphocytes: 0-3 cells/mm3

19. The Physical Characteristics and
Composition of the Cerebrospinal Fluid
Appearance Clear and colorless
Volume 150 mL
Rate of production 0.5mL/minute
Pressure 60-150 mm H2O
Composition
Protein
Glucose
Chloride
15-45 mg/dL
50-85 mg/dL
720-750 mg/dL
Number of cells 0-3 lymphocytes/ mm3

20. Clinical Notes
• Elevated Intracranial Pressure
– Meningitis, edema, tumor, abscess, hematoma
• Cloudy CSF
– presence of PMNs – meningitis, encephalitis
– Inc proteins – tuberculous meningitis,
poliomyelitis, multiple sclerosis
• Gross Blood
– Traumatic tap, subarachnoid hemorrhage

22. The Functions of the Cerebrospinal Fluid
1. Cushions and protects the central nervous system from
trauma
2. Provides mechanical buoyancy and support for the brain
3. Serves as a reservoir and assists in the regulation of the
contents of the skull
4. Nourishes the central nervous system
5. Removes metabolites from the central nervous system
6. Serves as a pathway for pineal secretions to reach the
pituitary gland

24. Formation
• CSF formation
– Mainly, choroid plexuses of lateral, third, and fourth
ventricles
– Some, ependymal cells lining the ventricles and from
the brain substance through the perivascular spaces
• Choroid plexuses
– Actively secrete CSF
– Actively transport metabolites from CSF to blood 
lower K+, Ca++, Mg++, HCO3- and glucose in CSF than
blood

25. Circulation
• Produced by Choroid
plexuses

27. Absorption
• CSF absorption by arachnoid villi that project into the
venous sinuses, especially superior sagittal sinus
• Arachnoid granulations
– elevation formed by grouping of arachnoid granulations
– Calcified with advanced age
• Some CSF probably is absorbed directly into the veins
in subarachnoid space
• Some CSF possibly escapes through the perineural
lymph vessels of the cranial and spinal nerves

29. Extensions of Subarachnoid Space
• Optic nerve to the back of the eyeball
• Other cranial and spinal nerves
• Arteries and veins of the brain and spinal cord
at points where they penetrate the nervous
tissue

30. Clinical Notes
• Increased ICP  compress the thin walls of
the retinal vein  congestion of retinal veins
 bulging of the optic disc  PAPILLEDEMA

31. Hydrocephalus
• Abnormal increase in the volume of the CSF within the
skull
– 1. Abnormal increase in the formation of fluid, ex. tumor
of choroid plexus
– 2. Blockage of circulation of the fluid, ex. tumor,
inflammatory exudate due to meningitis
– 3. Diminished absorption of the fluid, ex. Interference of
absorption in the arachnoid granulations due to
inflammatory exudate, venous thrombosis, pressure on
venous sinuses or obstruction of internal jugular vein
• Varieties
– Noncommunicating hyodrocephalus: (+) blockage at some
point in the circulation of CSF
– Communicating hydrocephalus: (-) obstruction

32. Normal
Communicating
Noncommunicating

33. BLOOD-BRAIN BARRIER

34. Structure
• Lumen of capillaries in the CNS is separated
from extracellular spaces around the neurons
and neuroglia by:
– Endothelial cells
– Continuous basement membrane
– Foot processes of the astrocytes
• Tight Junctions between endothelial cells
– Responsible for BBB

36. Permeability of BBB
• Inversely related to the size of the molecules
– Gases and water pass readily
– Glucose and electrolytes pass more slowly
– Large molecules MW > 60,000 remain within the
circulatory system
• Directly related to their lipid solubility
– Lipophilic molecules readily diffuse through the
barrier
– Hydrophilic molecules are excluded

37. Areas of the Brain NOT Protected by
Blood-Brain Barrier
• Pineal gland
• Posterior lobe of the pituitary
• Tuber cinereum
• Wall of the optic recess
• Vascular area postrema at the lower end of
the fourth ventricle

38. Clinical Notes
• BBB in fetus and newborn are not fully
developed, hence, toxic substances such as
bilirubin can readily enter the CNS 
KERNICTERUS
• Kernicterus is not possible in the adult

39. Drugs and Blood Brain Barrier
• Drugs that readily cross the BBB
– Thiopental, chloramphenicol, tetracyclines,
sulfonamide, tertiary amines like atropine, L-dopa
• Drugs that do not readily cross the BBB
– Penicillin, exogenous norepinephrine,
phenylbutazone, dopamine, quaternary amines
like atropine methylnitrate

40. BLOOD-CEREBROSPINAL FLUID
BARRIER

41. Structure
• Lumen of the capillary is separated from the
lumen of the ventricle by the following:
– 1. Endothelial cells
– 2. Continuous basement membrane
– 3. Pale cells with flattened processes
– 4. Continuous basement membrane
– 5. Choroidal epithelial cells
• Tight Junctions between choroidal cells serve as
the blood-CSF barrier

43. Permeability
• Free passage of water, gases, and lipid-soluble
substances from blood to CSF
• Macromolecules like proteins and hexoses
EXCEPT Glucose are unable to enter the CSF