Lecture on Fetal Circulation

Introduction

Blood Flow Through Heart
- Blood returns to the heart low in oxygen through the inferior and superior vena cava
- Drains into the right atrium → right ventricle → pulmonary artery
- Pulmonary artery carries deoxygenated blood to the lungs
- Lungs exchange gases: oxygen is absorbed, CO2 is exhaled
- Oxygenated blood returns via the pulmonary vein to the left atrium → left ventricle
- Left ventricle pumps oxygen-rich blood through the aorta to the body

Fetal circulation includes shunts to bypass non-functional lungs
Shunts in Fetal Circulation:
1. Ductus Venosus
2. Foramen Ovale
3. Ductus Arteriosus
Oxygen and nutrients supplied by placenta, not lungs

Placenta: Essential for providing oxygen and nutrients
- Connects to maternal circulation
- Transfers oxygen and nutrients to baby via umbilical cord
- Removes waste from baby’s circulation
Umbilical Cord Composition:
- 1 Umbilical Vein: Carries oxygenated blood to the fetus
- 2 Umbilical Arteries: Carry deoxygenated blood back to the placenta

Start at Placenta:
- Oxygenated blood travels via the umbilical vein
- Most blood bypasses liver via the ductus venosus
Right Atrium:
- Oxygenated blood flows from right atrium to left atrium via foramen ovale
- Deoxygenated blood flows to right ventricle
Right Ventricle to Pulmonary Artery:
- Blood shunted through ductus arteriosus to aorta
Aorta to Body:
- Mixed blood flows to descending aorta, distributed to body
- Deoxygenated blood returns to placenta via umbilical arteries

Umbilical Cord Cut:
- Stops blood flow through umbilical vein, ductus venosus closes
Lungs Begin to Function:
- Fluid in lungs cleared, alveoli open, resistance drops
- Pressure changes help close foramen ovale
- Ductus arteriosus closes due to reduced prostaglandins and increased oxygen

Patent Foramen Ovale (PFO):
- Foramen ovale may not close in some individuals
- Discussed under congenital heart defects in other videos

Reminder: Access the free quiz to test your understanding of fetal circulation.