Uteroplacental & Fetal Physiology Pt. 3 (Exam 2)

Question 1

What are the following abbreviations?

• MVU
• TOCO
• IUPC
• FSE
• CPD
• BPP

Answer 1

• MVU = Montevideo Units
• TOCO = Tocodynamometer
• IUPC = Intrauterine Pressure Catheter
• FSE = Fetal Scalp Electrode
• CPD = Cephalopelvic Disproportion
• BPP = Biophysical Profile

Question 2

What are the following abbreviations?

• DA
• DV
• FO
• HbF
• HbA
• FHR

Answer 2

• DA = Ductus Arteriosus
• DV = Ductus Venosus
• FO = Foramen Ovale
• HbF = Fetal Hemoglobin
• HbA = Adult Hemoglobin
• FHR = Fetal Heart Rate

Question 3

In fetal circulation, oxygen exchange occurs in the _____ instead of the lungs?

Answer 3

Placenta (organ of gas exchange)

Question 4

Fetal circulation is ______ in contrast to adult circulation which is _____ _____.

Answer 4

parallel : in series

Question 5

What are the three anatomic communications in fetal circulation?

Answer 5

• Ductus Venosus
• Foramen Ovale
• Ductus Arteriosus

Question 6

Pulmonary vascular resistance is ____ in fetus. Why is this?

Answer 6

High PVR

• Fetal lungs are collapsed & filled with fluid.
• very little pulmonary circulation.

Question 7

Systemic Vascular Resistance is _____ in the fetus. Why?

Answer 7

Low

• Placenta has a low resistance vascular bed.

Question 8

Fetal hgb has a ____ affinity for oxygen than adult hgb? This leads to what?

Answer 8

high affinity for oxygen

• efficient oxygen extraction from maternal blood
• optimizes oxygen supply

Question 9

The umbilical ____ brings oxygenated blood from the placenta to the fetus.

Answer 9

umbilical vein (1).

Question 10

The umbilical _____ send deoxygenated blood from the fetus back to the placenta.

Answer 10

umbilical arteries (2).

Question 11

What is the PO₂ of maternal blood in the placenta?
What is the (typical) O₂ saturation of the maternal blood?

Answer 11

PO₂ = 30-35 mmHg
SaO₂ = 80-85%

Question 12

How does the fetus maintain adequate oxygenation when exposed to a “low” O₂ saturation?

Answer 12

HbF will preferentially pull O₂ from the mom’s HbA due to its higher affinity.

Question 13

What are the cardiac output contributions of the right ventricle and left ventricle of the fetus?

Answer 13

RV = 67% of CO
LV = 33% of CO

Parallel circulation: both side of the heart provide systemic blood flow (not in-series like adults).

Question 14

Which fetal vessel allows oxygenated blood from the placenta to bypass portal circulation and go straight to the inferior vena cava?

Answer 14

Ductus Venosus

Question 15

Oxygenated and deoxygenated blood from the fetus’s lower and upper body mixes in the _____ before entering the _____?

Answer 15

Oxygenated and deoxygenated blood from the fetus’s lower and upper body mixes in the IVC before entering the Right atrium

Question 16

What aspect of fetal circulation allows oxygenated blood to flow from the Right atrium to the Left atrium?
What does this bypass?

Answer 16

Foramen Ovale (FO)

• Allows bypass of immature fetal lungs.

some blood goes into the right ventricle and into the immature pulmonary circulation

Question 17

What causes the high right-to-left shunt of the foramen ovale?

Answer 17

Due to pressure gradient from high fetal PVR.

fetal lungs are filled with amniotic fluid => high PVR

Question 18

What vessel diverts blood away from underdeveloped lungs?

Answer 18

Ductus Arteriosus: connects the pulmonary artery to descending aorta

Question 19

How much of the blood that goes from the RV to the PA ends up going through the pulmonary circulation?

Answer 19

only about 10%

Question 20

What fetal blood vessel connects the pulmonary artery and the descending aorta?

Answer 20

Ductus Arteriosus

Question 21

How much blood passes from the pulmonary artery through the ductus arteriosus to the _____?

Answer 21

about 90% of blood that travels from the RV to PA reroutes through the ductus arteriosus to the descending aorta

this perfuses the lower body of the fetus

Question 22

What vessel carries oxygenated blood from the placenta to the fetus?

Answer 22

Umbilical Vein (80-85% saturated)

Question 23

What vessel carries deoxygenated blood from the fetus to the placenta?

Answer 23

Umbilical arteries

Question 24

Where does blood from the umbilical vein go?

Answer 24

• ~50% to fetal portal circulation
• ~50% bypasses portal circulation through DV to IVC.

Question 25

The percentage of umbilical vein blood directed to the liver will increase in conjunction with ______ ____.

Answer 25

gestational age

Question 26

Does **all** blood from the RA bypass the lungs and go directly into the left atrium via the FO?

Answer 26

No. Some blood from the RA will go to the RV and then immature pulmonary circulation.

Question 27

Describe the path for most of the blood through fetal circulation.

Answer 27

RA → FO → LA → LV → Aorta → systemic circulation.

Question 28

What is greater in a fetus, PVR or SVR?

Answer 28

PVR

Question 29

The majority of fetal blood passes from the pulmonary artery through the ____ to the descending aorta to perfuse the lower body of the fetus.

Answer 29

DA (Ductus Arteriosus) *~90%*

Question 30

Where do the umbilical arteries originate?

Answer 30

descending aorta (common iliac arteries)

Question 31

What does the Ductus venosus do?

Answer 31

Shunts blood from the placenta (umbilical vein) to the IVC, bypassing the liver

Question 32

What does the Ductus arteriosus do?

Answer 32

Shunts blood from pulmonary artery to the descending aorta.

Question 33

What portion of the autonomic nervous system develops first and is predominant throughout fetal life?

Answer 33

Parasympathetic system

Question 34

What are the main environmental factors affecting fetal baroreceptors and thus SNS output?

Answer 34

Maternal BP & stress

Question 35

When does respiratory effort begin after delivery?

Answer 35

~30 - 90 seconds after delivery

Question 36

What respiratory changes occur at birth?

Answer 36

- ↓ Intrathoracic pressure = Air movement - Lung expansion = ↑ PaO₂ ↓ PaCO₂ - ↑ pH & P_AO₂ = **↓PVR**

Question 37

What does the decreased PVR upon birth do to pulmonary blood flow?

Answer 37

↑ pulmonary artery flow = RV output shifts to lungs = ↑ pulmonary blood flow

Question 38

What does surfactant do?

Answer 38

↓ surface tension = prevention of alveolar collapse = increased lung expansion and oxygen exchange

Question 39

When does surfactant production start?

Answer 39

24 - 28 weeks gestation

Question 40

The ductus arteriosus will constrict and close due to _________.

Answer 40

increased O₂ levels

Question 41

Why does the foramen ovale close?

Answer 41

Closes due to LA pressure exceeding RA pressure (shortly after birth)

Question 42

What causes LA pressure to exceed RA pressure in a neonate?

Answer 42

Clamping of the umbilical cord ⇒ ↑SVR ⇒ ↑LAP ⇒ ↓ right-to-left shunt

Question 43

This vessel closes with the clamping of the umbilical cord due to an increase in IVC pressure.

Answer 43

Ductus Venosus (DV)

Question 44

What four factors can cause PVR to remain elevated after delivery?

Answer 44

- Hypoxia - Acidosis - Hypovolemia - Hypothermia

Question 45

What drug class when used by a mom can cause premature constriction of the ductus arteriosus and thus persistent pulmonary hypertension of the newborn?

Answer 45

maternal NSAID use

Question 46

What things can lead to premature constriction of the Ductus arteriosus?

Answer 46

- NSAIDs - Preterm births - ↑ PA pressure