2. Fetal Circulation
• For the fetus the placenta is the oxygenator so
the lungs do little work
• RV & LV contribute equally to the systemic
circulation and pump against similar resistance
• Shunts are necessary for survival
– ductus venosus (bypasses liver)
– foramen ovale (R→L atrial level shunt)
– ductus arteriosus (R→L arterial level shunt)
3.
4. Transitional Circulation
• With first few breaths lungs expand and serve
as the oxygenator (and the placenta is
removed from the circuit)
• Foramen ovale functionally closes
• Ductus arteriosus usually closes within first 1-
2 days
5. Neonatal Circulation
• RV pumps to pulmonary circulation and LV
pumps to systemic circulation
• Pulmonary resistance (PVR) is high; so initially
RV pressure ~ LV pressure
• By 6 weeks pulmonary resistance drops and LV
becomes dominant
6. Normal Pediatric Circulation
• LV pressure is 4-5 x RV pressure (this is
feasible since RV pumps against lower
resistance than LV)
• RV is more compliant chamber than LV
7. • No shunts
• No pressure gradients
• Normal AV valves
• Normal semilunar
valves
• If this patient was
desaturated what
would you think?
75% 100%
20/ 90/
20/8
90/
60
100%
75%
8. CEREBROSPINAL FLUID & BBB
• INTRODUCTION :
• CSF is a colorless fluid that fills the ventricles of
the brain & subarachnoid space that surrounds
the brain & spinal cord
• CSF forms a thin layer of water jacket for brain &
spinal cord protecting them from mechanical
injury
• CSF regulates brain metabolism
• CSF analysis is an essential tool for the diagnosis
of neurological diseases
9. VENTRICULAR SYSTEM &
SUBARACHNOID SPACE
• The 4 ventricles are :2 lateral ventricles,a 3rd
ventricle & a 4th ventricle
• The 2 LVs communicate with the 3rd ventricle
through 2 independent openings called the
foramino of Monro
• The 3rd ventricle communicates with the 4th
through a narrow passage called the aqueduct of
Sylvius
• Each ventricle contains a bunch of epithelial
vascular tissue called the choroid plexus
10. SUBARACHNOID SPACE
• The brain & the spinal cord are covered by 3
layers of connective tissues, the piamater, the
arachnoidmater & the duramater
• Two potential spaces in between : the
subarachnoid space & the subdural space
• SAS is enlarged at few places to form 4 major &
many minor cisterns
• Superior cistern, cerebellomedullary cistern
(cisterna magna ), pontine cistern
&interpeduncular cistern
11. • Minor cisterns are :cistern of optic disc,lamina
terminalis, corpus callosum, lateral sulcus &
lumbar cistern ( L2 – S2 )
• Arachnoid granulations : a collection of villi
that project from the arachnoid into the
subdural venous sinuses
• The cerebral ventricles communicate with the
sub arachnoid space through openings in the
4th ventricle, the foramen of Magendie & the
foramen of Lushka
12. FORMATION, CIRCULATION &
ABSORPTION OF CSF
• FORMATION : Choroid plexuses are the major
source ; the other sources are the blood
vessels of the subependymal regions & the pia
• RATE OF FORMATION : CSF accounts for 70 –
160 ml, i.e 10 % of the total intracranial
volume
• Formed at the rate of 0.35 ml / min, or 20 ml /
hr or 500 ml / day ; totally replaced 4 -5 times
daily
13. MECHANISM OF FORMATION
• 1. PASSIVE DIFFUSION : By the thin walled
vessels of choroid plexus from the blood
plasma into the extracellular space
surrounding the choroid plexus
• 2.ACTIVE TRANSPORT : Na + -K+ pump in the
apical surface of choroid plexus pumps Na +
into the ventricular cavity; Cl- moves passively
into CSF; osmotic gradient enhances H2O
flow; in the basal surface, Cl- is exchanged for
HCO3 and H+ for Na+
14. • 3.FACILATED DIFFUSION :penetration of
substances into brain is directly proportional
to their lipid solubility; lipid insoluble
substances like hexoses and aminoacids enter
by facilitated diffusion.
• CSF formation occurs in 2 steps :
• Ultrafiltration and
• Active secretion
16. CIRCULATION
• Lateral ventricle Third ventricle Fourth
ventricle subarachnoid space cerebral
hemispheres
• Obstruction of the foramens cause distension
at various levels
• ABSORPTION : Through the arachnoid villui;
• The factors facilitating the movement of fluid
are the oncotic pressure and the hydrostatic
pressure of the CSF
17. FUNCTIONS OF CSF
• 1. Protection from mechanical injury : due to
difference in SG , brain floats freely in CSF ;
impact of injuries is less
• 2.Provides microenvironement for the brain
cells : CSF ensures constancy in the external
environment of neurons by buffering changes
in blood with the brain interstitial fluid
• 3. Role in homeostasis : The changes in blood
PO2 , PCO2 and pH are transmitted to
chemo- sensitive respiratory neurons and
18. • 4. Removal of proteins & waste products :
• CSF serves as lymphatics in the brain ;
removes proteins and waste products of
metabolism especially H+ , lactate and CO2
through its sink action
19. APPLIED PHYSIOLOGY
• LUMBAR PUNCTURE : Sampling of CSFis an
important diagnostic tool in neurology ; in the
interspace between L1 –L2 or L2 –L3
• EXAMINATION OF CSF : COLOR :
• Normal CSF is transparent and colorless ;
presence of turbidity indicates proteins and
cells; determination of the types of cells,
proteins and glucose concn. are very useful
20. Meningitis : protein and cells are more ;
glucose concn. Is low
CSF culture confirms the nature of infection
Cerebral haemorrhage : CSF is bloody or
yellow and protein is raised
Encephalitis : clear ; lymphocyte and protein
are high
Brain tumors : clear ; mild increase in
lymphocyte and protein
21. • Queckenstedt test : performed to
demonstrate spinal subarachnoid block;
• Normal CSF pressure in the recumbent
posture is 100 – 180 cm H2O
• HYDROCEPHALUS : Increase in CSF volume
enlargement of the ventricles ; intracranial
CSF pressure is usually high ;
• Two types : communicating and non
communicating
22. • EFFECTS OF INCREASED ICP :
• Space occupying lesion in the cranial cavity -->
raised ICP /CSF pressure ; detected by doing
ophthalmoscopic exmn.of the fundus of the
eye – papillodema
• Clinical significance :
• LP to be avoided in increased ICP ; leads to
herniation of the cerebellum and medulla -
CONING
23. BLOOD BRAIN BARRIER
• A special barrier that exists between the blood
and the brain tissue is the BBB
• BBB selectively allows small molecules and
prevents large molecules thus protecting the
neurons from harmful agents
• Blood CSF Barrier : in the choroid plexus
• CSF Brain barrier :
24. Anatomical basis of BBB
• Formed by 2 special structures :
• 1. capillary endothelial cells of the brain are
joined by tight junctions
• 2. capillaries are surrounded by foot processes
of astroglia
• CIRCUMVENTRICULAR ORGANS : Remain
outside the BBB ; include OVLT ,SFO , Area
postrema in medulla , Posterior pituatory and
median eminence of hypothalamus and the
pineal gland
25. Functions of BBB
• Maintains the constancy of ions in the brain
fluids
• Protects the brain neurons from harmful
agents
• Prevents the escape of neurotransmittors
from brain into circulation
• Disruption of BBB helps to identify the
location and extent of brain lesion
• Influences drug penetrability into brain
26. CLINICAL IMPORTANCE
• KERNICTERUS : Deposition of bilirubin in the
basal ganglia
• BRAIN TUMOR : BBB is absent at the site of
tumor ; in confirming and locating the tumor
• INFECTION AND INJURY : Breaking of BBB
allows drug penetration
• USE OF HYPERTONIC SALINE : temporarily
weakens the BBB
