Fetal Circulation

Fetal circulation

During intra uterine life placenta is the sourse of nutrition and site of elimination of waste. There are several structure in addition to the placenta and umbilical cord.

 The umbilical vein :

• leads from umbilical cord to the underside of the liver and carries blood rich in oxygen and nutrients.
• It has branch that joins the portal vein and supply the liver.

 Ductus venosus (from vein to vein)

• this connects the umbilical vein to the inferior vena cava.
• At this point the blood mixes with the deoxygenated blood returning from the lower parts of the body.

 The foramen ovale:

• temporary opening between the atria that allows the majority of the blood to pass across the left atrium (no respiration)

The ductus arteriosis (from artery to an artery)

• this leads from the bifurcation of the pulmonary artery to the descending aorta,entering it just beyond the point where the carotid and subclavian arteries leave.

The hypogastric arteries:

• these arteries off from the internal iliac arteries and become umbilical arteries when they enter the umbilical cord they return blood to the placenta.
• From placenta the blood passes along the umbilical vein through the abdominal wall to  the undersurface of the liver,
• gives off branches to the left lobe of the liver and receives deoxygenated blood from the portal vein,. (unmixed blood)
• The ductus venosus carries blood to the inferior vena cava which mixes with the blood from  the lower body.
• From here the blood passes into  the right atrium
• Most of it is directed across through the foramen ovale in to the left atrium.
• Following its normal route it enters left ventricle and passes into aorta.
• The heart and brain gets a supply relatively well oxygenated. (coronary and carotid arteries are early branches of aorta.)
• Blood collected from the upper parts of the body returns to the right atrium in the superior vena cava.
• This blood is depleated of oxygen and nutrients.
• This stream of blood crosses the stream enteringfrom the inferior vena cava and passes into the right  ventricle.
•  the two streams remain separate because of the shape of the atrium.
• But there is a mixing of 25 % of the blood allowing a little oxygen and food to be taken into the lungs through pulmonary arteries. (necessary for the development)
• Adaptation to the extra uterine life
• At birth the baby breath and blood is drawn to the lungs through the pulmonary arteries.
• It is then collected and returned to the left atrium via pulmonary veins.
• The placental circulation ceases soon after birth. (less blood returns to the right side of the heart.)
• Pressure in the left side is greater
• This result in the closure of flap over foramen ovale. (stops blood flow from right to left)
• Establishment of pulmonary respiration result in the rise of oxygen concentration  in the blood stream.
• Causes the ductus arteriosus to constrict and close.
• The cessation of  the placental circulation result in collapse of the umbilical vein, ductus venosus and hypogastric arteries.
• Umbilical vein-ligamentum teres.
• D V- ligamentum venosum
• D A- ligamentum arteriosum
• Hypogastric arteries -obliterated hypogastric arteries
• F O-fossa ovalis

Closure of :

• umbilical artery-functional closure-instantaneous….anatomical closure 2 to 3 months
• U V-obliteration little later than  U A
• D A fun -soon after establishing pul  circulation
• F O- fun soon after birth
• Anatomical 1 year