Topic 8: Fetal Circulation Flashcards
In the fetus, organs that do not function until birth – (3)
Lungs
Kidneys
GI Tract
Wastes and CO2 are eliminated via diffusion into the maternal blood
Exchange occurs via the placenta- what two ways?
Inside the uterus
Attached to baby via the umbilical cord
Placenta - definition
–way of communication between mother and
baby
Site of exchange of nutrients/ wastes
Umbilical Artery - def
–carries blood away from the fetus to the placenta
Carries wastes and CO2
LOW O2 Content!
Umbilical Vein
–carries blood from the placenta to the fetus
Carries nutrients and O2
HIGH O2 Content
Fetal Capillaries
–Umbilical arteries and veins branch into
these capillaries located inside the intervillous spaces in the placenta
Intervillous Spaces
–Spaces filled with maternal blood from uterine arterioles. Drained by Uterine veins.
The placenta communicates with the mother’s cardiovascular system via?
uterine blood vessels
Nutrients travel from mother’s blood vessels to the intervillous space via ?
uterine arteries.
Diffuse from the intervillous spaces into the fetal capillaries
The concentration of hemoglobin in fetal blood is about what % different than maternal blood??
50% higher
Fetal hemoglobin has a greater affinity for oxygen than maternal blood – how much more oxygen can it carry?
Can carry 30-35% more oxygen
Is there direct mixing of maternal and fetal blood?
NO
Exchange of gases–CO2, O2, CO
Accomplished via?
diffusion
Exchange of gases–O2 – rate of extraction?
20-30mL O2/min extracted
Short interruption in blood flow can be fatal to fetus
Exchange of gases–CO2, O2, CO
-Depends on rate of what?
Depends on delivery not rate of diffusion
Exchange Nutrients/ Electrolytes - examples?
Amino Acids, Free Fatty Acids, Carbohydrates, Vitamins
Exchange is rapid and increases as pregnancy increases
Exchange Nutrients/ Electrolytes -
Exchange is rapid and increases as what?
pregnancy increases
Placental circulation resistance?
very low
Transfer of Maternal Antibodies - starts when?
fetus makes components of what?
Late first trimester–fetus makes components of complement
Start of immunological competence
What type of Immunoglobulins primarily?
at what week?
–Primarily IgG
Transported from mother to fetus (at about 14
weeks)
Provides passive immunity
Newborns produce own IgG, but don’t reach adult levels until about age 3
Hormone Production in placents begins what month?
4th month
Hormone Production
–placenta produces enough of what?
to support pregnancy, should corpus luteum fails
progesterone
The placenta Continues to produce what kind of hormones?
Rises until end of pregnancy
estrogenic hormones
Estriol
Blood passes from the fetus to the placenta via __ umbilical arteries
Branch of what??
2
internal iliac arteries
Sat ~58
Oxygenated blood returns from the placenta via 1 umbilical vein – what is the Oxy Sat %??
sat ~80%
umbilical vein – Goes to the liver of the fetus where it divides into what 2 branches?
–Joins hepatic portal vein-> Liver (1/3)
—Ductus Venosus-> IVC (2/3)
Sphincter mechanism in ductus that controls blood flow through the liver
In the IVC, oxygenated blood via what?? meets deoxygenated blood from the lower body
Sat falls to about 67%
ductus venosus
Most fetal blood passes through what in the Heart?
Foramen Ovale (Hole between the Right and Left Atria) Blood entering from the IVC is guided toward the foramen ovale to the Left Atrium
(most does not go from the RV to the lungs)
In the LA, blood mixes with the very small amount of blood returning from the pulmonary veins and goes where?
to the LV
LV pumps the oxygenated blood into the aorta, this blood perfuses what two areas?
Perfuses the brain and myocardium
Getting highest O2 content available
Fetal blood returning to the heart from the SVC take what path through heart?
bypasses the Foramen Ovale and enters the RA
Goes to the RV and pumped to the PA
Pulmonary Vascular Resistance is so high that what happens to the blood supposed to go out the pulmonary arteries? what path does it take?
95% of this blood bypasses the pulmonary arteries
Travels across the ductus arteriosus to the descending aorta
Ductus arteriosus connects PA and Aorta
Pulmonary Vascular Resistance is ?
so HIGH
At the common iliac branch to the internal and external iliacs
Part of that blood flowing systemically will flow through the internal iliacs to where? for what?
the internal iliacs to the umbilical artery
Will go to the placenta for nutrient/waste exchange
The only fetal vessel to carry fully oxygenated blood is what?
umbilical vein
Blood entering the aorta from the LV and perfusing the head and heart has higher ____ than the blood perfusing the rest of the body.
oxygen content
At birth, what systems start to function?
the Pulmonary, Renal and Digestive Systems
There are 3 shunts present in the fetal circulation that normally close after birth:
Ductus Arteriosus
Foramen Ovale
Ductus Venosus
Umbilical arteries functionally close when?
a few minutes after birth
Umbilical arteries will eventually fill with? (after birth)
connective tissue
Distal portion will become fibrous cords
Medial umbilical ligaments
IN BABY
Umbilical arteries complete closure when?
2-3 months
Umbilical Vein Collapse when?
shortly after the umbilical arteries
Umbilical Vein remains as the?
ligamentum teres hepatis
- Lower margin of the falciform ligament. Attaches the umbilicus to the liver in baby!
Blood from the placenta may enter newborn for some time after birth via what?
Umbilical vein
What happens to the Ductus Venosus after birth?
Collapses
Remains as Ligamentum Venosum
Fibrous cord on the inferior surface of the liver
Occurance of a Patent Ductus Venosus?
extremely rare
Less than 20 reported world wide
Foramen Ovale - after birth?
Anatomical (permanent) closure occurs within the first year of life
Usually closes after birth to become the Fossa Ovalis
The first breath causes the lungs to expand and blood flow to the lungs increases.
Blood returning to the LA increases its pressure, And pressure in the RA falls.
First breath presses the septum primum against the septum secundum causes functional closure of the foramen ovale at birth.
Constant apposition leads to fusion of the septa.
cyanotic periods of newborns caused by what?
The Foramen Ovale – first days of life, closure is reversible
Crying by baby creates a right to left shunt and can account for the cyanotic periods of newborns.
When does permanent (anatomical) closure of the septa occure?
within the 1st year of life
After a year, if the Foramen Ovale has not closed, it is referred to as what?
prevalence of this happeninf?
a Patent Foramen Ovale (PFO).
27% prevalence of PFO
Most patients are a symptomatic
Umbilical Arteries becomes after birth?
Medial Umbilical Ligaments
Ductus Arteriosus becomes after birth?
Ligamentum Arteriosum
Umbilical Vein becomes after birth?
Ligamentum Teres (Round Ligament)
Ductus Venosus becomes after birth?
Ligamentum Venosum
Foramen Ovale becomes after birth?
Fossa Ovalis
Ductus Arteriosus Closes via what ?
contraction of the muscular wall immediately after birth.
Mediated by Bradykinin which is released by the lungs during the initial inflation.
After the first breath, the lungs fill with air instead of fluid
Pulmonary vascular resistance falls
Pulmonary blood flow increases
Ductus Arteriosus Closure mediated by?
Mediated by Bradykinin which is released by the lungs during the initial inflation.
Ductus initially protects the pulmonary vasculature from what?
overload
Ductus Arteriosus Closure time in a full term infant?
Takes about 1-2 days to close in a full term infant
Ductus Arteriosus complete obliteration of the lumen takes?
1-3 months
