The MOTHER'S fetal blood flows from the placenta through the umbilical cord. The less oxygenated blood flows through two umbilical arteries and the higher oxygenated blood flows through a single umbilical vein. The blood vessels in the placenta are course through the chorionic plate and forms into larger stem villi which again becomes into finely branched villi and finally, end as smaller terminal villi - CAPILLARY NETWORK.
The gaseous exchange in the fetal lung is not happening and the function of the lung is inactive. A Certain amount of right ventricular blood bypasses the lungs and the chambers of fetal heart work in parallel. In an adult, the chambers of the heart work in series. Because of this the fetal brain and the fetal heart receive more oxygenated blood. The connection between the placenta and the umbilicus of the fetus is the umbilical cord. The umbilical cord contains one umbilical vein and two umbilical arteries. The umbilical vein carries the mother's oxygenated blood into the fetal circulation through the umbilical cord. First, you want to know the three terms which are present only in the fetal circulation.
DUCTUS VENOSUS - arterial blood(umbilical vein) passes directly through LIVER and enter into INFERIOR VENA CAVA.
FORAMEN OVALE - The blood which comes from the lower part of the trunk of the fetus is a venous blood which will be mixed with arterial blood at this point(where the ductus venosus enter inferior vena cava which bypasses the liver and joins the inferior vena cava). Here the bloodstream advances through the valve of inferior vena cava and directed through the foramen ovale(a shunt between the right atrium and the left atrium) to the left atrium and the blood passes left ventricle to the aorta.
DUCTUS ARTERIOSUS - Blood from right ventricle communicates with aortic arch through Ductus Arteriosus.
FETAL CIRCULATION
The arterial blood(umbilical vein) passes directly in LIVER through its branch DUCTUS VENOSUS and passes into INFERIOR VENA CAVA(blood comes from the lower part of the trunk is a venous blood is mixed with arterial blood at this point of inferior vena cava). The blood enters the right atrium which shunts through FORAMEN OVALE to the left heart(left atrium)----to brain-------becomes less oxygenated blood---------through SUPERIOR VENA CAVA---------RIGHT ATRIUM------directed through(passes) FORAMEN OVALE to left atrium-----passes left ventricle------to the AORTA.(Note: The blood goes through inferior vena cava to the brain and from brain, it comes to RIGHT ATRIUM through superior vena cava).
The blood from the right ventricle passes through the DUCTUS ARTERIOSUS and communicates with AORTIC ARCH.
CHANGES IN FETAL CIRCULATION:
After the breath of a child(ON FIRST INSPIRATION)----blood in the lungs passes through PULMONARY ARTERY into the LEFT ATRIUM. This increases pressure in this chamber due to the collection of blood from PULMONARY ARTERY, due to this the pressure in the RIGHT ATRIUM falls which lead to foramen ovale closure and kept so.
After foramen ovale is closed, from right atrium blood rushes to RIGHT VENTRICLE. Now the lung sucks the blood from INFERIOR VENA CAVA and SUPERIOR VENA CAVA which stops the blood to go through the Ductus Arteriosus(PORTAL SYSTEM STARTS FUNCTIONING), this makes the Ductus Arteriosus collapse which becomes OBLITERATED and SHRINKS.
*NOTE 1: The hypogastric arteries contract and thrombose to form obliterated hypogastric arteries of the ADULT.
*NOTE 2: When ligature applied to the umbilical cord immediately after the baby starts first inspiration. This makes the arterial blood supply from the umbilical vein to cut off, which makes the walls of the umbilical vein to agglutinate and the vein is obliterated and remains as a cord-like ligament which passing to the ligamentum teres.
*NOTE 3: Ductus Venosus collapses, shrinks and forming a very small remnant which once played a very important role in Fetal circulation.
*source-internet
PLACENTA is doing the functions of ADULT LUNGS, LIVER and other BLOOD FORMING ORGANS in fetal circulation.
credit - Mudaliar and Menon's (clinical and obstetrics).
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