4. Fetal Circulation
Transcript of 4. Fetal Circulation
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Fetal Circulation
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Fetal Circulation is the circulatory
system of a humanfetus, oftenencompassing the
entire fetoplacentalcirculation that alsoincludes the umbilicalcord and the blood
vessels within theplacenta that carryfetal blood.
The fetal circulationworks differently fromthat of born humans,because the lungs are
not in use: the fetusobtains oxygen andnutrients from themother through the
placenta and theumbilical cord.[1]
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Placenta is an organ that
connects thedeveloping fetus tothe uterine wall toallow nutrient uptake,
waste elimination, andgas exchange via themother's bloodsupply.
averages 22 cm(9 inch) inlength and 22.5 cm(0.81 inch) in
thickness
weighs approximately500 grams (1 lb)
has a dark reddish-blue
or maroon color. It connects to the fetus
by an umbilical cord
develops from same
sperm and egg cellsthat form the fetus, andfunctions as afetomaternal organ with
two components:a. fetal part (Chorion
frondosum)
b. maternal part
(Decidua basali
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Placenta Function Nutrition and immunity
- allows the transfer of nutrients and oxygen fromthe mother to the fetus and the transfer of waste
products and carbon dioxide back from the fetus to themother.
- IgG antibodies pass through the human placenta,providing
protection to the fetus in uterus.
Secretes hormones that are important duringpregnancy.
a. Human Chorionic Gonadotropin (hCG).
- can be found in maternal blood and urine during
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Human ChorionicGonadotropin (hCG).-- the hormone
analyzed bypregnancy test; afalse-negative resultfrom a pregnancy test
may be obtainedbefore or after thisperiod.
- Women's blood
serum (-) for hCG by1-2 weeks after birth,is proof that allplacental tissue is
delivered.
hCG is only present
during pregnancybecause it is secreted
by the placenta, whichis present only[8]during pregnancy.
hCG ensures that the
corpus luteumcontinues to secreteprogesterone andestrogen.
Progesteronesecretion decreases,the endometrial liningslough off andpregnancy will be lost.
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Progesteroneprevents pretermlabor by reducingmyometrial
contraction. Levels ofprogesterone are highduring pregnancy.
Estrogen is referredto as the "hormone ofwomen" because itstimulates the
development ofsecondary female sexcharacteristics.
- contributes to thewoman's mammary
gland development inpreparation forlactation andstimulates uterine
growth toaccommodate
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Human PlacentalLactogen (hPL[Human ChorionicSomatomammotropin]) - This hormone islactogenic and growth-promoting properties.
- promotes mammarygland growth inpreparation for lactationin the mother.
- It regulates maternalglucose, protein, fatlevels so that this isalways available to the
fetus.
The placenta alsoprovides a reservoir ofblood for the fetus,delivering blood to it incase of hypotensionand vice versa
Fetal surfacesmooth & glistening sholtz
Maternal surface red
& freshlike duncan Large particles such
as bacteria cannotpass through thebarrier
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Placental expulsionbegins as aphysiological
separation from thewall of the uterus.
The period from justafter the fetus isexpelled until just afterthe placenta isexpelled is called thethird stage of labor.
The placenta isexpelled within 1530minutes of the baby
being born.
Placental expulsioncan be managed bygiving oxytocin via
intramuscular injectionfollowed by cordtraction to assist indelivering the
placenta.
Alternatively, it can bemanaged by allowingthe placenta to be
expelled withoutmedical assistance.
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The umbilical cord also called the birth cord or
funiculus umbilicalis is theconnecting cord from the developingfetus to the placenta.
comes from the same zygote as the
fetus and contains two arteries (theumbilical arteries) and one vein (theumbilical vein), buried withinWharton's jelly.
The umbilical vein supplies the fetus:oxygenated, nutrient-rich blood fromthe placenta.
the umbilical arteries return the
deoxygenated, nutrient-depletedblood.
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joins the placenta,which transfersmaterials to and from
the mother's bloodwithout allowing directmixing.
is about 50centimeters (20 in)long and about 2centimeters (0.75 in)in diameter.
Wharton's jelly, agelatinous substancemade contains one
vein, which carriesoxygenated, nutrient-rich blood to thefoetus, and two
arteries that carrydeoxygenated,nutrient-depletedblood away.
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Associated Problems:
too short
- mechanical abruptio
- uterine inversion Associated Problems:
too long
cord coil
cord compression cord prolapsed
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Amniotic sac is the sac in which the
fetus develops inamniotes.
a tough but thintransparent pair ofmembranes, whichhold a developingembryo until birth.
The inner membrane,the amnion, containsthe amniotic fluid andthe fetus.
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The outer membrane,the Chorion, containsthe amnion and is partof the placenta.
It encloses theamniotic cavity and
the embryo. The amniotic cavity
contains the amnioticfluid.
On the outer side, theamniotic sac isconnected to the yolksac, to the allantois
and, through the
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Amniotic Fluid Also known as liquor
amnii is thenourishing andprotecting liquid
contained by theamniotic sac of apregnant woman.
The amniotic sac
grows and begins tofill with water,proteins,carbohydrates, lipids
and phospholipids,
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Purposes Protects fetus against
blows or pressure onmothers abdomen
Protects the fetus
against the suddenchanges in temp.since liquid changestemp. more slowly
than air
Protects the fetusfrom infection
Provides freemovement for the
Amniocentesisremoval of amnioticfluid to diagnosedchromosomal
abnormalities Meconium stained
amniotic fluid in nonbreech presentation is
a sign of fetal distress
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During weeks 811,the fetus begins toswallow and urinate,
which is why theamniotic fluid containsfetal urine.
The volume ofamniotic fluidincreases as the fetusgrows approximately800 ml.
The amount of fluiddeclines when thebaby is born.
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The fore waters arereleased when theamnion ruptures. This is
commonly known as thetime when a woman's"water breaks (BOW).
When this occurs during
labour at term, it isknown as "spontaneousrupture of membranes"(SROM).
If the rupture precedeslabour at term, however,it is referred to as"premature rupture ofmembranes" (PROM).
The majority of thehind waters remaininside the womb until
the baby is born.
Artificial rupture ofmembrane (ARM), amanual rupture of theamniotic sac, can alsobe performed torelease the fluid if theamnion has not
spontaneouslyruptured.
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Oligoscantyamount of
Amniotic fluidless than 500ccwhich may
result to fetaldistress
because no
enough fluid toequalize the
pressure
Polyhydramnios excessive
amount ofexcessive
Amniotic fluid> 1500-2000cc w/c
may result topreterm labor
or uterine
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Foramen Ovale
also called ostiumsecundum of Born orfalx septi
allows blood to enter
the left atrium from theright atrium.
one of two fetal cardiacshunts
closes at birth and lungsbecomes functional
It later forms the fossaovalis - an embryonic
remnant of the foramen
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Ductus Venosus
shunts approximatelyhalf of the blood flow ofthe umbilical veindirectly to the inferiorvena cava.
allows oxygenatedblood from the placentato bypass the liver
closes during the firstweek of life in full-termneonates; may takemuch longer to close in
pre-term neonates.
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After it closes, the
remnant is known asligamentum venosum.
If the ductus venosusfails to occlude afterbirth, the individual issaid to have an
intrahepaticportosystemic shunt(PSS).
Fetal circulation. The ductus venosus (red)connects the umbilical vein to the inferiorvena cava
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Ductus Arteriosus is a temporary fetal
blood vessel that
connects the aortaand the pulmonaryartery before birth.
the ductus arteriosusacts as a "short cut"
that allows blood tobypass the deflatedlungs and go straight
out to the body.
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After birth, when thelungs are needed to addoxygen to the blood, the
ductus arteriosusnormally closes.
Closure of the ductusarteriosus usually
occurs at birth as levelsof certain chemicals,called prostagladins,change, and the lungsfill with air.
If the ductus arteriosuscloses correctly, theblood pumped from theheart goes to the lungs,
back into the heart, and
The blood returningfrom the lungs andmoving out of the
aorta carries oxygento the cells of thebody.
In some infants, theductus arteriosusremains open (orpatent), and theresulting heart defectis known as patentductus arteriosus.
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The Flow Oxygenated blood
enters the umbilicalvein from theplacenta
oxygenated blood
bypass the liver viaductus venosus andcombines withdeoxygenated bloodin the inferior &superior vena cava
Enters the rightatrium
Enters the foramen
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Some blood enters theright ventricle but most
Enters pulmonaryartery with some bloodgoing to the lungs tosupply oxygen and
nourishment Flows to ductus
arteriosus
Enters descending
aorta ( blood going tothe lower extremities)
Goes back to theplacenta via umbilical
arteries
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The core conceptbehind fetal circulationis that fetalhemoglobin has a
higher affinity foroxygen than doesadult hemoglobin,which allows a
diffusion of oxygenfrom the mother'scirculatory system tothe fetus.
The branch of theumbilical vein thatsupplies the right lobeof the liver first joins
with the portal vein
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Summary
Structure Location Function
Placenta Attached to the uterus Gas exchange during fetal life
UmbilicalArteries
2 arteries in the cord Carry unoxygenated bloodfrom the fetus
Umbilical Vein 1 vein in the cord Carry oxygenated blood fromthe fetus
Foramen Ovale Opening in the interatrial septum(bet. the R & L atrium)
To shunt blood from the Ratrium to the L atrium so thatblood can be supplied tobrain, heart & kidney
Ductus Venosus Accessory vein connectingumbilical vein into fetal liver &inferior vena cava
To supply blood to the liver
DuctusArteriosus
Connection bet. fetal lungs & theaorta
Shunting of the larger portionof the blood away from thelungs & directly to the aorta