Fetal and Neonatal Circulation

Question 1

What are the four bypasses in the fetal circulation?

Answer 1

Placenta, ductus venosus, foramen ovale, ductus arteriosus

Question 2

How much blood goes to and from the placenta in fetal circulation?

Answer 2

50%

Question 3

Is the blood oxygenated or deoxygenated as it arrives from the placenta into the right atrium?

Answer 3

It is initially oxygenated, and mixes with deoxygenated blood before going into the IVC

Question 4

What does the ductus venosus allow for?

Answer 4

Bypass of the liver before going to the IVC

Question 5

How much of the blood in the IVC (69%) goes from the RA to the RV? RA to the LA?

Answer 5

42 and 27% respectively

Question 6

How much blood goes to the RV in total in fetal circulation? The LV?

Answer 6

66% (21% from the SVC, 3% that nourished the heart, 42% from the IVC); 34% (27% from the LA, 7% from the developing lungs)

Question 7

Where do the RV and LV both pump blood into? Where does most of the blood go through from the RV to get to that destination? What is the output from the RV and LV called?

Answer 7

Descending aorta;
ductus arteriosus (3/4 of blood from RV)
combined cardiac output

Question 8

Where does most of the blood from the descending aorta go to?

Answer 8

To the two umbilical arteries and later the placenta

Question 9

Why does the lung have high resistance in fetal circulation?

Answer 9

1. Lung hypoxic leading to vasoconstriction

2. Blood vessels not inflated

Question 10

Compared to adult blood flow, how does blood flow in the fetus?

Answer 10

Mostly parallel in the fetus, in series in the adult!

Question 11

Where is the greatest O2 saturation and O2 partial pressure in the fetal circulation?

Answer 11

In the umbilical veins

Question 12

As we go from the umbilical veins to the RV and LV, why do the O2 sat and pO2 levels decrease?

Answer 12

Because of the low levels in the lungs for the LV; and the heart and SVC blood for the RV

Question 13

What does blood being pumped in parallel mean for organs?

Answer 13

Organs are able to get some oxygenated blood

Question 14

What happens when a newborn loses placental circulation?

Answer 14

Newborn breathes on its own:
Increased pulmonary blood flow
Ductus venosus, foramen ovale, ductus arteriosus close

Question 15

What triggers the first breath?

Answer 15

Mild hypoxia, hypercapnia, tactile stimuli, cold skin

Question 16

How much pressure is needed for first breath?

Answer 16

60 mm H20, compared to 2.5 mm H20 for the adult

Question 17

What makes breathing easier? What is a consequence if one doesn’t have this?

Answer 17

Alveoli open and type II alveolar pneumocytes produce surfactant;
Respiratory distress syndrome (premature births)

Question 18

At birth, what three things happen?

Answer 18

Pulmonary vascular resistance decreases, pulmonary blood flow increases, mean pulmonary arterial pressure decreases

Question 19

At birth, why does PVR decrease?

Answer 19

1. Pulmonary bv’s not crushed
2. Breathing leads to higher pO2, more vasodilation
3. Prostaglandins cause vasodilation

Question 20

What four functions does the placenta perform?

Answer 20

Equivalent of:
1. Lungs (gas exchange) 2. GI tract (nutrition) 3. Liver (nutrition, waste removal) 4. Kidneys (fluid and electrolyte balance, waste removal)

Question 21

What happens with insufficiency of the placenta?

Answer 21

Type II intrauterine growth restriction (IUGR)

Question 22

What if gas exchange is interfered with?

Answer 22

Fetal asphyxia, or baby smaller than normal

Question 23

Where does maternal blood build up in the placenta?

Answer 23

Intervillous space

Question 24

What enables gas exchange in the placenta?

Answer 24

Chorionic villus (capillaries)

Question 25

From the mother back to the mother, trace out the blood flow; how is gas exchanged?

Answer 25

Spiral arteries go to intervillous space and back to maternal veins
O2 to the fetus, CO2 back to the mother

Question 26

Even with similar pO2, why does the umbilical vein have a higher O2 sat than the uterine vein?

Answer 26

Because fetal Hg binds O2 tighter than the mother Hg (ensures enough O2 sent to the organs;
Babies with higher HR (CO) than mother
Concentration of fetal Hg > mother Hg

Question 27

What happens in the neonatal circulation once the placenta doesn’t have blood flow?

Answer 27

systemic vascular resistance doubles; increased aortic, LV, LA pressures

Question 28

With respiratory activity by neonate, what happens to the pulmonary vascular resistance? When then happens with pulmonary vessels?

Answer 28

Greatly decreased;
No longer compressed
arteriolar vasodilation seen with higher blood O2 and prostaglandin release

Question 29

With lung expansion, what happens to the right and left heart?

Answer 29

Pulmonary arterial pressure, RV, RA pressures go down

Increased LA pressure (more blood through lung)

Question 30

What leads to the foramen ovale closing?

Answer 30

Increased LA pressure, decreased RA pressure

Question 31

What happens if you don’t seal the foramen ovale?

Answer 31

Patent foramen ovale

Question 32

What happens within three hours after birth to ductus venosus?

Answer 32

Vascular smooth muscle of ductus venosus constricts, becomes ligamentum venosum

Question 33

Consequence of ductus venosus not closing

Answer 33

Portosystemic shunt

Question 34

What happens to the ductus arteriosus?

Answer 34

Closes with constriction with increased plasma pO2, lower blood prostaglandins, bradykinin involvement

Question 35

What happens if the ductus arteriosus does not close?

Answer 35

Patent ductus arteriosus (pulmonary hypertension, maybe CHF and arryhthmias)

Question 36

What happens with aortic pressure exceeding pulmonary artery pressure?

Answer 36

Blood flow through ductus arteriosus reverses

Question 37

What do the elimination of the shunts mean for O2 sats and PO2 in the circulation?

Answer 37

They increase!

Question 38

What are some birth defects besides the patent ductus arteriosus?

Answer 38

1. Coarctation of the aorta (ductus arteriosus invaded the descending aorta)
2. Ventricular septal defects (blood flow from LV to RV and CHF)
3. Atrial Septal Defects (LA to RA, leading to pulmonary hypertension, right heart enlargement, heart failure)
4. Tetralogy of Fallot (pulmonary stenosis, dextroposition of aorta, RV hypertrophy, VSD) baby blue!