Fetal and Neonatal Circulation Flashcards
which organs in the fetus are nonfunctional? what happens to the blood supply to these organs?
the lungs and liver (partially functional)
special vessels help blood bypass these organs
what extra organ must fetal blood pump through?
the placenta
where does oxygenated blood originate from and how does it travel to the heart in the fetus?
originates from the placenta
umbilical vein-> ductus venosus (bypasses liver)-> inferior vena cava
what happens to blood from the superior and inferior vena cava in the heart in the fetus?
40% of inferior vena cava blood flows through the foramen ovale into the left atrium
rest of IVC and all of SVC blood flows to the right ventricle
where does blood from the SVC come from?
deoxygenated blood from forequarters
describe the output of the fetal heart.
3/4 blood from the right ventricle goes through the ductus arteriosus into the descending aorta (rest goes to lungs)
sum of both ventricles called combined cardiac output (66% from right ventricle and 34% from left)
contrast the fetal and adult circulation
while in adults, the two sides of the heart work in series, in the fetus they work in parallel
where does blood from the fetal descending aorta go primarily? where does the rest go?
hypogastric arteries-> umbilical arteries->placenta
small amt goes to hindquarters and mesentery
compare the O2 saturation in the right vs the left ventricles of the fetal heart.
R-55%
L-65%
describe cardiopulmonary adjustments at birth
loss of placental circulation, increase in pulmonary blood flow and closure of ductus venosus, foramen ovale and ductus areteriosus
newborn must breathe on its own
what triggers a child’s first breath?
mild hypoxia, hypercapnia, tactile stimuli and cold skin
what does the first inspiratory effort require? how much does the lung fill?
60 cm H2O
40 ml
what makes infant’s breathing easier? what is the result of the failure of these mehcanisms?
when alveoli are open, type two pneumocytes make surfactant
respiratory distress syndrome
at birth, what is the change in pulmonary vascular resistance, pulmonary blood flow and mean pulmonary arterial pressure?
sharp drop in resistance
great increase in blood flow
drop in pulmonary arterial pressure
what causes the decrease in pulmonary vascular resistance at birth?
pulmonary blod vessels are no longer crushed, breathing causes increased PO2 and vasodilation and local prostaglandins cause vasodilation
why does pulmonary arterial pressure decrease at birth?
because the vascular resistance decrease is greater than the rise in blood flow that accompanies it
what four organs does the placenta functionally replace?
lungs (gas exchange), GI tract, liver (nutrition and waste removal), and kidneys (fluid and electrolyte balance and waste removal)
what causes type two intrauterine growth restriction?
insufficiency of the placenta
when does the fetal heart begin to beat? what changes occur to the heart rate?
one month after fertililzation
begins at 65 b/min and increases to 140 near birth
when are all of the organs of the fetus formed? what systems require more than 9 months for full development?
in the first 2-3 months
the kidneys, liver and nervous system
what is the intervillous space of the placenta filled with? what is it between?
maternal blood
between the endometrium on the maternal side and the villi on the fetal side
what does the mature chorionic villus contain and what is it covered with?
contains fetal arterial and venous blood in capillaries along with cytotrophoblasts and mesenchyme
covered with a thin layer of synctiotrophoblast
what empties into the intervillous space and what drains it?
mature placental spiral arteries fill it and it is drained by maternal veins
how does the PO2 of the intervillous space compare to theat of the umbilical vein?
it is about the same
compare the hemoglobin saturation of the intervillous space and the umbilical vein.
the umbilical vein has much higher saturation because of the fetal hemoglobin
what does closure of the placental circulation do to peripheral resistance and blood pressure?
causes peripheral resistance to double and increases aortic and left ventricular pressure
what causes the closure of the forament ovale?
left atrial pressure becomes more than the right and closes the valve of the foramen ovale
a permanent seal should form in a few months-years
what causes the reversal of pressures in the atria?
here is a decrease in right atrial pressure and the return from the lungs increases left atrial pressure
what does the ductus venosus bypass? what does it become in the neonate?
the liver
becomes the ligamentum venosum
how does the ductus venosus close?
three hours after birth, the smooth muscle of the ductus venosus constricts and occludes the shunt possibly by increased PO2 and reduced prostaglandins
what happens with failure of the ductus venosus closure?
portosystemic shunt
what does the ductus arteriosus become? how does it close?
becomes the ligamentum arteriosum
first the wall constricts and then thrombi occlude the lumen
what signals the ductus arteriosis to close?
increased PO2 (from flow reversal), decreased circulating prostaglandin and bradykinin from the lung
what does a patent ductus arteriosus cause? what is one reason this may happen?
pulmonary hypertension, congestive heart failure and cardiac arrhythmias
may happen with high altitude birth because of the low O2 levels
what does closure of the foramen ovale and ductus arteriosus do?
it establishes a separate right and left circulatory system
causes increases in O2 saturation and PO2
when does pulmonary circulation absorb the fluid filling the alveoli in the fetal lung? what happens to the rest?
during labor and after birth
the rest is absorbed by pulmonary lymphatics or expelled out of the trachea
how is a small patent ductus arteriosus found clinically?
there is a murmer
what causes coarctation of the aorta?
smooth muscle of the ductus arteriosis invades the descending aorta and constricts after birth
what is the risk of a large ventricular septal defect?
congestive heart failure
what is the consequence of a large atrial septal defect?
pulmonary hypertension, right heart hypertrophy and heart failure
what is involved in the tetralogy of fallot?
pulmonary stenosis, right ventricular hypertrophy, ventricular septal defet and dextroposition of the aorta (receives input from both ventricles)
