Fetal Circulation

Question 1

Where is blood for the fetus oxygenated?

Answer 1

In the placenta

Question 2

In utero, describe whether the following are low or high:
Systemic pressure
Pulmonic pressure

Answer 2

Systemic - low

Pulmonic - high

Question 3

Name the FOUR additional components/structures in the fetal circulatory system not required in extra uterine life

Answer 3

• Ductus Arteriosus
• Ductus Venosus
• Foramen Ovale
• Two Hypogastric Arteries

Question 4

Where is the tricuspid valve located?

Answer 4

On the right side of the heart between the atrium and ventricle

Question 5

Where is the bicuspid or the mitral valve located?

Answer 5

On the left side of the heart between the atrium and ventricle

Question 6

What percentage of the cardiac output to the fetal lungs receive?

Answer 6

5-10%

Question 7

How does oxygenated blood travel from the placenta to the fetus?

Answer 7

Via the umbilical vein

Question 8

What is the average oxygen saturation in the umbilical vein?

Answer 8

80%

Question 9

Which vein does the umbilical vein join up with once inside the body?

Answer 9

The hepatic portal vein

Question 10

Which temporary structure connects the portal vein with the inferior vena cava to bypass the liver?

Answer 10

Ductus Venosus

Question 11

When the oxygenated blood from the umbilical vein mixes with the deoxygenated blood in the inferior vena cava, what is the approximate resulting O2 saturation percent?

Answer 11

67%

Question 12

Which temporary structure connects the right atrium to the left atrium?

Answer 12

Foramen Ovale

Question 13

What percentage of blood from the inferior vena cava passes straight through the foramen ovale and what does this achieve?

Answer 13

Approximately 33% which ensures that the coronary arteries and brain receive blood with the highest PaO2

Question 14

Which side of the foramen ovale can the valve be closed from?

Answer 14

The left side to prevent backflow

Question 15

Name the temporary structure which allows blood to bypass the lungs and flow from the pulmonary artery to the descending aorta?

Answer 15

Ductus Arteriosus

Question 16

Why does a small quantity of blood pass through the pulmonary artery?

Answer 16

To nourish the lung tissue

Question 17

What temporary structures branch off from the iliac arteries and eventually become the umbilical arteries once in the umbilical cord?

Answer 17

Hypogastric areteries

Question 18

Name the FOUR stages of fetal lung development and when they occur

Answer 18

Embryonic - 0-5 weeks
Pseudoglandular - 5-17 weeks
Canalicular - 17-24weeks
Saccular / Terminal air sac stage - 24/26 to 37+ weeks

Question 19

Describe what happens during the embryonic stage of lung development

Answer 19

The respiratory bud arises from the ventral surface of the foregut

Question 20

Describe what happens during the pseudoglandular stage of lung development

Answer 20

Bronchial tree from the trachea to terminal bronchioles are formed, pulmonary, arterial and venous systems develop

Question 21

Describe what happens during the canalicular stage of lung development

Answer 21

Distal airways develop and epithelial cells subdivide into:

• Type 1 pneuomocytes~ which are necessary for gas exchange
• Type 2 pneumocytes~ which are necessary for surfactant production

Question 22

What unique function do pneuomocytes possess?

Answer 22

The ability to change function from a secretory cell producing lung fluid in utero, to a cell capable of absorption in post natal life

Question 23

Describe what happens during the saccular stage of lung development

Answer 23

• Formation of terminal sacs, alveolar ducts and eventually alveoli.
• Accompanied by increasing surfactant production from 23 weeks

Question 24

What happens to the following when baby takes its first breath:
Pulmonary Vascular Resistance
Pulmonary Blood Flow

Answer 24

Pulmonary Vascular Resistance - decreases

Pulmonary Blood Flow - increases

Question 25

What happens to the following when the cord is clamped: Ductus Venosus Inferior Vena Cava Blood Flow Systemic Vascular Resistance

Answer 25

Ductus Venosus - begins to close Blood Flow - decreases Vascular Resistance - increases

Question 26

What triggers the foramen ovale to begin to close?

Answer 26

The increased pulmonary blood flow increases the pulmonary venous return which raises the pressure in the left atrium

Question 27

What triggers the ductus arteriosus to begin to close?

Answer 27

The rise in PaO2 and a fall in circulating prostaglandin levels

Question 28

How many hours following birth is the ductus arteriosus normally fully closed?

Answer 28

12 hours

Question 29

Prior to birth approximately how many millileters of fluid is in the lungs of a healthy term fetus?

Answer 29

Approx 80-100ml

Question 30

How is lung fluid removed from the lungs in utero?

Answer 30

Can be swallowed and excreted by the kidney into the amniotic fluid

Question 31

How is lung fluid expelled from the baby following birth?

Answer 31

Expelled via the mouth during birth and by initial respirations and absorbed via the lymphatic system

Question 32

When aerating the lungs at birth, why does the neonate generate an opening pressure of at least 20 cm H2O?

Answer 32

To overcome: The viscosity of lung fluid The surface tension within the fluid filled lung The elastic recoil and resistance of the tissue of the chest wall, lungs and airways

Question 33

What stimulates the new born baby to cry?

Answer 33

Towards the end of labour the fetus is relatively hypoxic With placental separation, the O2 content of the blood decreases further and CO2 rises This causes chemoreceptors in the carotid arteries to set up a reflex stimulus in the respiratory centre

Question 34

What are the two main functions of surfactant?

Answer 34

To reduce surface tension in the alveoli, allowing them to expand more easily To prevent atelectasis at the end of each expiration

Question 35

What is surfactant?

Answer 35

It is composed of 90% lipids and 10% protein and secreted in to lung fluid from around 22 weeks

Question 36

What other factors can initiate respirations?

Answer 36

Peripheral stimulation/ handling at birth Relatively cold environment of labour room Exposure to sensory stimuli~ light, gravity sound. Cord clamping