Fetal Circulation | American Heart Association

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Fetal Circulation



qBegins to develop toward the end of third week.
qHeart starts to beat at the beginning of the fourth week.

Structures involved in fetal circulation
        1. Umbilical vein
´Carries oxygenated blood from placenta to fetus.
´Number: 1
2. Umbilical artery
´Carries deoxygenated blood from fetus to placenta.
´Also known as Hypogastric arteries.
´Number: 2
3. Ductus Arteriosus:
´Protect lungs against circulatory overload.
´Allows right ventricle to strengthen.
´Carries mostly medium oxygen saturated blood.
4. Ductus Venosus
´Fetal blood vessel connecting umbilical vein to inferior venacava.
´Blood regulated via sphincter.
´Carries mostly high oxygenated blood.
5. Formen Ovale
´Connect right and left chamber of heart.
´Transfer highly oxygenated blood from right antrium to left antrium.

Fig: Structure of parts involved in fetal circulation

Flow chart of fetal circulation

Umbilical veins carries oxygenated blood from placenta to fetus.
               ⇙                                                ⇘
70-80% of oxygenated blood                            20-30% of oxygenated blood
goes to liver through portal vein.                       mixed with inferior venacava and
                         ⇓                                                   forms ductus venosus.
Blood in liver comes out through                                            ⇓ 
hepatic vein and mix with inferior                                            
venacava.                                                                               
                      ⇘                                              ⇙                             
Goes to Right Antrium.
⇓
Foramen ovale allows the mixed blood to pass to the right ventricle and left antrium by passing through lungs.
          Right ventricle                                                                           Left Antrium
         ⇙                                                ⇘
Goes to pulmonary artery by passing                                     Enter to left ventricle.
through lungs.
                ⇓                                                 ⇓
Mixed blood Passes to Aorta through                                      Mixed blood passes 
ductus arteriousus.                                                                     to aorta.
          ⇘                                           ⇙
Mixed blood distributes to the fetal tissues and other body parts.
⇓
Fetal tissues uses oxygen saturated blood.
⇓
Remaining deoxygenated blood carried by two umbilical arteries to placenta from fetal tissues.
⇓
Placenta transfers deoxygenated blood to maternal circulation and  gets oxygenated blood.
⇓
Umbilical vein carries the oxygenated blood and the process gets continued.


Changes in circulatory system after birth

  •          The placenta is replaced by the lungs as the respiratory organ.
  •         The lungs and the pulmonary vessels expand thereby significantly lowering the resistance to blood flow.
  •          Subsequently the pressure in the pulmonary artery and right side of the heart is decreased.
  •          Pressure in the left side of the heart is increased.
  •          The increasing pressure of left side of the heart decreases the vascular resistance of lungs therefore blood enters to lungs as a respiratory exchange.  
Changes in shunts after birth
  •        Closure of Ductus venosus
  •        Closure of Ductus Arteriosus
  •        Closure of Foramen ovale

Overview of Fetal Circulation 



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