Fetal Circulation | Cardiovascular system | Step 1 Simplified

Summary

This script explores fetal circulation, highlighting the role of the placenta for gas exchange instead of the lungs. It details key shunts like the ductus arteriosus, umbilical arteries, and the foramen ovale, which ensure efficient oxygen delivery to vital organs. Post-birth, the script explains how changes in pulmonary vascular resistance, atrial pressures, and prostaglandin levels lead to the closure of these shunts, transitioning the baby to adult circulation. It also briefly touches on congenital heart diseases.

Takeaways

• 🌟 The placenta is the organ for gas exchange in fetal circulation, not the lungs.
• 🚫 Fetal lungs have high pulmonary vascular resistance, preventing blood flow through them efficiently.
• 🔄 Deoxygenated blood from the veins is diverted from the pulmonary artery to the aorta through the ductus arteriosus.
• 🔄 Umbilical arteries carry deoxygenated blood to the placenta for oxygenation.
• 🌀 The umbilical vein returns oxygenated blood to the fetus, contrary to typical arterial function.
• 🚸 The ductus venosus shunts blood from the umbilical veins, bypassing the liver to increase oxygen delivery to the heart.
• 🕳️ The foramen ovale allows oxygenated blood to bypass the lungs by moving from the right to the left atrium.
• 🔄 The ductus arteriosus shunts deoxygenated blood from the superior vena cava to the aorta, bypassing the lungs and directing it to the placenta.
• 🌬️ At birth, the first breath decreases pulmonary vascular resistance, allowing blood to flow through the lungs.
• 🔧 After birth, the closure of the foramen ovale and ductus arteriosus occurs due to increased oxygen levels and decreased prostaglandins.

Q & A

What is the primary organ for gas exchange in fetal circulation?

The primary organ for gas exchange in fetal circulation is the placenta, not the lungs.

Why are the fetal lungs not capable of respiration until week 25?

The fetal lungs are not capable of respiration until week 25 because they are still developing and have very high pulmonary vascular resistance, making it difficult for blood to flow through them.

What is the role of the ductus arteriosus in fetal circulation?

The ductus arteriosus diverts deoxygenated blood from the pulmonary artery to the aorta, bypassing the lungs and directing it towards the placenta for gas exchange.

How do umbilical arteries and veins function differently in fetal circulation compared to adult circulation?

In fetal circulation, umbilical arteries carry deoxygenated blood to the placenta, while umbilical veins return oxygenated blood to the fetus. In adult circulation, arteries carry oxygenated blood and veins carry deoxygenated blood.

What is the purpose of the ductus venosus in fetal circulation?

The ductus venosus bypasses the hepatic circulation, allowing oxygenated blood from the umbilical veins to bypass the liver and directly enter the inferior vena cava, ensuring efficient delivery of oxygen to the heart.

Why does the foramen ovale allow blood to flow from the right atrium to the left atrium in fetal circulation?

The foramen ovale allows oxygenated blood from the right atrium to flow directly to the left atrium, ensuring that blood rich in oxygen is directed to vital organs like the brain and heart.

What changes occur in the circulatory system at birth to transition from fetal to adult circulation?

At birth, the baby takes its first breath, which increases lung volume and decreases pulmonary vascular resistance. This leads to closure of the foramen ovale and ductus arteriosus, and a decrease in prostaglandins causes closure of the ductus venosus.

How does the closure of the foramen ovale occur after birth?

The closure of the foramen ovale occurs after birth as the left atrial pressure exceeds the right atrial pressure due to increased blood flow to the lungs, causing the flap to close like a trapdoor.

What is the role of prostaglandins in maintaining the patency of the ductus arteriosus during fetal life?

Prostaglandins, specifically prostaglandin E1 and E2, keep the ductus arteriosus open during fetal life by preventing it from closing.

How can a patent ductus arteriosus be treated after birth if it fails to close naturally?

A patent ductus arteriosus can be treated with indomethacin, a non-steroidal anti-inflammatory drug that blocks prostaglandin production, leading to closure of the ductus arteriosus.