FETAL CIRCULATION IN ENGLISH

                                                    

                                  FETAL CIRCULATION IN ENGLISH

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 FETAL  CIRCULATION- The lungs of developing fetus are  inactive. Fetus obtains its oxygen and nutrients, and excretes its waste, via the mother’s blood. this exchange take place in the placenta. The blood flow from placenta to fetus tissues and back to placenta is know as fetal circulation

 

PLACENTA- This is a temporary structure that  allows exchange of substances between  circulatory systems of mother and fetus. The placenta is firmly attached to the uterine wall and consists of an extensive network of fetal capillaries bathed in maternal blood. Although the fetal capillaries are in very close proximity to the maternal blood supply yet the two circulations are completely separate.

 

VENOUS BLOOD FLOW TO FETUS

One umbilical vein collects oxygenated blood  from placenta and travel to infant through umbilical cord. There is a special vein (Ductus venosus) which is a continuation of the umbilical vein that returns blood directly into the fetal inferior vena cava, and most blood, therefore, bypasses the non-functional fetal liver. Fetal inferior vena cava pour oxygenated blood into right atrium of fetal heart.

 

There are two special adaptations in fetal heart to bypass the lungs as it is already oxygenated blood.

•       Foramen ovale- This forms a valve-like opening  allowing blood to flow from  right atrium to the left atrium to bypass lungs.

•       Ductus arteriosus- This small vessel connects the pulmonary artery to the descending thoracic aorta and diverts more blood into the systemic circulation, meaning that very little blood passes through the fetal lungs. Oxygenated blood is  pumped into fetal systemic circulation

 

RETURN OF BLOOD TO PLACENTA

 

Two placental arteries arises from internal iliac artery and carry less oxygenated blood to placenta through umbilical cord . In this way the fetal circulation is completed.

 

CHANGES AT BIRTH

When the baby takes its first breath the lungs inflate for the first time, increasing pulmonary blood flow. Blood returning from the lungs increases the pressure in the left atrium, closing the flap over the foramen ovale and preventing blood flow between the atria. Blood entering the right atrium is therefore diverted into the right ventricle and into the pulmonary circulation through the pulmonary veins.

As the pulmonary circulation is established  blood oxygen levels increase, causing constriction and closure of the ductus arteriosus.  When the placental circulation ceases, soon after birth, the umbilical vein, ductus venosus and umbilical arteries collapse, as they are no longer required.