Fetal and Neonatal Circulation

Question 1

which organs in the fetus are nonfunctional? what happens to the blood supply to these organs?

Answer 1

the lungs and liver (partially functional)

special vessels help blood bypass these organs

Question 2

what extra organ must fetal blood pump through?

Answer 2

the placenta

Question 3

where does oxygenated blood originate from and how does it travel to the heart in the fetus?

Answer 3

originates from the placenta

umbilical vein-> ductus venosus (bypasses liver)-> inferior vena cava

Question 4

what happens to blood from the superior and inferior vena cava in the heart in the fetus?

Answer 4

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

Question 5

where does blood from the SVC come from?

Answer 5

deoxygenated blood from forequarters

Question 6

describe the output of the fetal heart.

Answer 6

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)

Question 7

contrast the fetal and adult circulation

Answer 7

while in adults, the two sides of the heart work in series, in the fetus they work in parallel

Question 8

where does blood from the fetal descending aorta go primarily? where does the rest go?

Answer 8

hypogastric arteries-> umbilical arteries->placenta

small amt goes to hindquarters and mesentery

Question 9

compare the O2 saturation in the right vs the left ventricles of the fetal heart.

Answer 9

R-55%

L-65%

Question 10

describe cardiopulmonary adjustments at birth

Answer 10

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

Question 11

what triggers a child’s first breath?

Answer 11

mild hypoxia, hypercapnia, tactile stimuli and cold skin

Question 12

what does the first inspiratory effort require? how much does the lung fill?

Answer 12

60 cm H2O

40 ml

Question 13

what makes infant’s breathing easier? what is the result of the failure of these mehcanisms?

Answer 13

when alveoli are open, type two pneumocytes make surfactant

respiratory distress syndrome

Question 14

at birth, what is the change in pulmonary vascular resistance, pulmonary blood flow and mean pulmonary arterial pressure?

Answer 14

sharp drop in resistance
great increase in blood flow
drop in pulmonary arterial pressure

Question 15

what causes the decrease in pulmonary vascular resistance at birth?

Answer 15

pulmonary blod vessels are no longer crushed, breathing causes increased PO2 and vasodilation and local prostaglandins cause vasodilation

Question 16

why does pulmonary arterial pressure decrease at birth?

Answer 16

because the vascular resistance decrease is greater than the rise in blood flow that accompanies it

Question 17

what four organs does the placenta functionally replace?

Answer 17

lungs (gas exchange), GI tract, liver (nutrition and waste removal), and kidneys (fluid and electrolyte balance and waste removal)

Question 18

what causes type two intrauterine growth restriction?

Answer 18

insufficiency of the placenta

Question 19

when does the fetal heart begin to beat? what changes occur to the heart rate?

Answer 19

one month after fertililzation

begins at 65 b/min and increases to 140 near birth

Question 20

when are all of the organs of the fetus formed? what systems require more than 9 months for full development?

Answer 20

in the first 2-3 months

the kidneys, liver and nervous system

Question 21

what is the intervillous space of the placenta filled with? what is it between?

Answer 21

maternal blood

between the endometrium on the maternal side and the villi on the fetal side

Question 22

what does the mature chorionic villus contain and what is it covered with?

Answer 22

contains fetal arterial and venous blood in capillaries along with cytotrophoblasts and mesenchyme
covered with a thin layer of synctiotrophoblast

Question 23

what empties into the intervillous space and what drains it?

Answer 23

mature placental spiral arteries fill it and it is drained by maternal veins

Question 24

how does the PO2 of the intervillous space compare to theat of the umbilical vein?

Answer 24

it is about the same

Question 25

compare the hemoglobin saturation of the intervillous space and the umbilical vein.

Answer 25

the umbilical vein has much higher saturation because of the fetal hemoglobin

Question 26

what does closure of the placental circulation do to peripheral resistance and blood pressure?

Answer 26

causes peripheral resistance to double and increases aortic and left ventricular pressure

Question 27

what causes the closure of the forament ovale?

Answer 27

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

Question 28

what causes the reversal of pressures in the atria?

Answer 28

here is a decrease in right atrial pressure and the return from the lungs increases left atrial pressure

Question 29

what does the ductus venosus bypass? what does it become in the neonate?

Answer 29

the liver

becomes the ligamentum venosum

Question 30

how does the ductus venosus close?

Answer 30

three hours after birth, the smooth muscle of the ductus venosus constricts and occludes the shunt possibly by increased PO2 and reduced prostaglandins

Question 31

what happens with failure of the ductus venosus closure?

Answer 31

portosystemic shunt

Question 32

what does the ductus arteriosus become? how does it close?

Answer 32

becomes the ligamentum arteriosum

first the wall constricts and then thrombi occlude the lumen

Question 33

what signals the ductus arteriosis to close?

Answer 33

increased PO2 (from flow reversal), decreased circulating prostaglandin and bradykinin from the lung

Question 34

what does a patent ductus arteriosus cause? what is one reason this may happen?

Answer 34

pulmonary hypertension, congestive heart failure and cardiac arrhythmias
may happen with high altitude birth because of the low O2 levels

Question 35

what does closure of the foramen ovale and ductus arteriosus do?

Answer 35

it establishes a separate right and left circulatory system

causes increases in O2 saturation and PO2

Question 36

when does pulmonary circulation absorb the fluid filling the alveoli in the fetal lung? what happens to the rest?

Answer 36

during labor and after birth

the rest is absorbed by pulmonary lymphatics or expelled out of the trachea

Question 37

how is a small patent ductus arteriosus found clinically?

Answer 37

there is a murmer

Question 38

what causes coarctation of the aorta?

Answer 38

smooth muscle of the ductus arteriosis invades the descending aorta and constricts after birth

Question 39

what is the risk of a large ventricular septal defect?

Answer 39

congestive heart failure

Question 40

what is the consequence of a large atrial septal defect?

Answer 40

pulmonary hypertension, right heart hypertrophy and heart failure

Question 41

what is involved in the tetralogy of fallot?

Answer 41

pulmonary stenosis, right ventricular hypertrophy, ventricular septal defet and dextroposition of the aorta (receives input from both ventricles)