fetal circulation

in embryo where is o2 nutrients coming from?

maternal circulation via placenta

what are the 3 cardiac shunts that aid for proper development?

foramen ovale (between R and L atria)

Ductus Arteriosus (between PA and aorta)

Ductus Venosus (bypass liver)

umb artery towards pacenta

deoxygenated

umb vein back to fetus

(oxygenated)

what are two special feature of fetal circulation?

intra and extra cardiac shunts

both ventricles work in parallel rather than in series

placenta is a source of

nutrients and gas exchange

what is foramen ovale purpose?

Allow blood to skip the lungs.

what are the functions of the ductus arteriosus?

Vessel connecting the pulmonary artery → aorta, allowing blood to bypass the lungs.

series

co=RV= LV output

parallel

co= RV+LV output

RV accounts for a little less than half of CO. LV pumps the rest

which heart has the LV and RV with similar thickness?

fetal/neonatal heart

what is something the fetal heart does that is opposite of mature?

rv pumps against higher resistance than LV

BF to lungs is a fraction of…

RV output

Do fetal lungs extract oxygen? What is their function before birth?

• No. Fetal lungs do not extract oxygen because gas exchange occurs at the placenta.

• Instead, fetal lungs secrete fluid, which helps with normal lung development.

• After birth, the lungs fill with air and become the site of oxygen exchange.

first organ to receive maternal substances (oxygen, glucose, amino acids)

liver

which shunt bypasses the liver

ductus venousus

is the placenta high or low resistance circuit?

low resistance ( a lot of blood will pass through)

which has the greatest vascular resistance?

pulmonary circulation

what does shunt help with?

o2 distribution and also work load distribution

what would happen if we didnt have sunt?

overload of RV

What provides preload (ventricular input) to the fetal right ventricle?

SVC, IVC, CS

What provides preload (ventricular input) to the fetal left ventricle?

• Foramen ovale (FO) ≈ 46%

• Pulmonary veins (lungs) ≈ 9%

Why does the fetal left ventricle receive most of its blood through the foramen ovale?

Because the foramen ovale shunts blood directly from the right atrium to the left atrium, bypassing the nonfunctional fetal lungs.

Which ventricle receives more preload in the fetus?

Left ventricle (≈55%)

what are some fetal heart defects

premature closure of FO

premature closure of DA

what would premature closure of FO cause?

extra RV workload - grows excessively (hypertrophy)

reduced LV workload - atrophy

what would premature closure of DA?

lower R through FO than lungs

Extra RV and LV workload- improper development

purposed of shunts

proper development of ventricles

direct umbilical vein blood toward brain and heart

Whos PO2 is greater?

moms

which will saturate lower levels of PO2 than parental?

fetal Hb

how to deal with low o2 environment?

foramen ovale

which organs get the best o2 saturation?

brain and heart

what specialize shunt ensures proper development of LV?

FO and ductus arteriosus help distribute the workload?

what does fetal Hb not interact with?

2,3- BPG

What does 2,3-BPG do to adult hemoglobin?

• 2,3-BPG binds to adult hemoglobin (HbA).

• It decreases hemoglobin's affinity for oxygen, causing hemoglobin to release

Which fetal vessel has the highest oxygen saturation and PO₂?

Umbilical vein

Why does oxygen saturation decrease from the umbilical vein to the lower limbs?

Because oxygenated blood mixes with deoxygenated blood as it circulates through the fetus.

Why can the fetus survive with such a low PO₂?

Because fetal hemoglobin (HbF) has a higher affinity for oxygen than adult hemoglobin, allowing it to efficiently bind oxygen even at low PO₂.

compensation for low O2

high co

hct increases with gestation

increased in cerebral and coronary blood flow

from fetus to adult your cardiac output…

decreases

from fetus to adult you HR….

decreases

from fetus to adult your BP

increases

at birth, your mean pulmonary arterial pressure

decreases

an increase in left atrial pressure helps close what?

foramen ovale

What happens to pulmonary vascular resistance (PVR) when a newborn takes its first breath?

PVR decreases because oxygen causes the pulmonary blood vessels to vasodilate, eliminating fetal hypoxic vasoconstriction.

What happens after pulmonary vascular resistance decreases at birth?

• Pulmonary blood flow increases.

• Venous return to the left atrium increases.

• Left atrial pressure (LAP) increases.

• The increased LAP helps close the foramen ovale.

What happens to systemic vascular resistance (SVR) when a newborn takes its first breath?

It increases: Closure of placental circulation

What happens after systemic vascular resistance increases at birth?

decrease venous return to RA

decrease right atrial pressure

increase in pulmonary blood flow

increase venous return to LA

increase LAP

functional changes at birth

blood flows through ductus arteriosus becomes primarily left to right

no placental prostaglandins (constriction)

higher po2 causes constriction