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Flashcards in Fetal Circulation Deck (36):

Where is blood for the fetus oxygenated?

In the placenta


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

Systemic - low

Pulmonic - high


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

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


Where is the tricuspid valve located?

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


Where is the bicuspid or the mitral valve located?

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


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



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

Via the umbilical vein


What is the average oxygen saturation in the umbilical vein?



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

The hepatic portal vein


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

Ductus Venosus


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?



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

Foramen Ovale


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

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


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

The left side to prevent backflow


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

Ductus Arteriosus


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

To nourish the lung tissue


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

Hypogastric areteries


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

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


Describe what happens during the embryonic stage of lung development

The respiratory bud arises from the ventral surface of the foregut


Describe what happens during the pseudoglandular stage of lung development

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


Describe what happens during the canalicular stage of lung development

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


What unique function do pneuomocytes possess?

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


Describe what happens during the saccular stage of lung development

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


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

Pulmonary Vascular Resistance - decreases
Pulmonary Blood Flow - increases


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

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


What triggers the foramen ovale to begin to close?

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


What triggers the ductus arteriosus to begin to close?

The rise in PaO2 and a fall in circulating prostaglandin levels


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

12 hours


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

Approx 80-100ml


How is lung fluid removed from the lungs in utero?

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


How is lung fluid expelled from the baby following birth?

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


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

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


What stimulates the new born baby to cry?

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


What are the two main functions of surfactant?

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


What is surfactant?

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


What other factors can initiate respirations?

Peripheral stimulation/ handling at birth

Relatively cold environment of labour room

Exposure to sensory stimuli~ light, gravity sound.

Cord clamping