USMLE Step 1 Physiology Review 56 16 Fetal Circulation

USMLE Step 1 Physiology Review 56 16 Fetal Circulation

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Play USMLE Audio MP3 56 16 Fetal Circulation Below

Begin 56 16 Fetal Circulation Transcription

Now for some questions on fetal circulation. What structure in the fetal heart provides a pathway for the returning venous blood to go right across the right atrium into the left atrium?

  • The foramen ovale.

What does this become after birth?

  • Fossa ovalis in the atria septum

Where is most of the venous blood coming from the flow that actually goes across the right atrium into the foramen ovale in the fetal heart?

  • The inferior vena cava

What is the net result?

  • To reduce preload of the right ventricle and thus reduce the amount of blood being pump out of the right side of the heart

What structure provides a pathway between the pulmonary artery and the aorta?

  • The ductus arteriosus

What is the net effect of this?

  • To bypass the lung

What structure brings blood from the placenta to the portal system and to the inferior vena cava?

  • The umbilical vein

Is this blood already oxygenated?

  • Yes, by the mother.

What structures bring blood from the descending aorta back to the placenta?

  • The umbilical arteries

What structure provides a pathway for blood from the umbilical vein to the inferior vena cava?

  • The ductus venous

What structure directs umbilical blood flow?

  • The valve of the inferior vena cava

Student doctor please pause the tape and summarize the information on fetal circulation.

The foramen ovale in the fetal heart provides a pathway for the returning venous blood to go right across the right atrium into the left atrium. After birth, this becomes fossa ovalis in the atria septum. The most of the venous blood that is the flow that actually go across the right atrium into the foramen ovale in the fetal heart come from the inferior vena cava. The net result is to reduce preload of the right ventricle and thus reduce the amount of blood being pump out of the right side of the heart. The ductus arteriosus provides a pathway between the pulmonary artery and the aorta. The net effect of this is to bypass the lung. The umbilical vein brings blood from the placenta to the portal system and to the inferior vena cava. This blood is already oxygenated by the mother. The umbilical arteries structures bring blood from the descending aorta back to the placenta. The ductus venous provides a pathway for blood from the umbilical vein to the inferior vena cava. The valve of the inferior vena cava directs umbilical blood flow.

****END OF TRANSCRIPTION****

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