Fetal circulation

Neonatal circulation

Placenta and umbilical vessels

• Placenta functions as fetal lungs and the oxygenated blood passes into left umbilical vein which enters the liver.

• The umbilical arteries(right and left) carry deoxygenated blood from the fetus to the placenta

Problems of fetal circulation

• The lungs do not function in fetal life.

• Hence the left heart and the systemic circulation are maintained by number of by-pass mechanisms namely;

• Foramen ovale

• Ductus arteriosus

• Ductus venosus

The left umbilical vein

• Highly oxygenated,nutrient rich blood comes from the left umbilical vein.

• Much of this blood is diverted into ductus venosus, which connects the left umbilical vein to IVC in the liver

left umbilical vein

Sphincter mechanism in the liver

• This regulates the flow of remaining blood from umbilical vein into IVC through hepatic veins.

• It is generally agreed that a physiological sphincter exists and prevents overloading of heart when the venous flow in the left.umb.vein is high(eg.during uterine contractions)

Foramen ovale

• After a short course in IVC the blood enters the right atrium and much of it passes into the left atrium through foramen ovale(a gap in the interatrial septum)

Ductus arteriosus

• Low oxygenated blood from SVC and some amount of blood from IVC pass into right ventricle and thence into pulmonary artery(trunk).

• 90% of this blood is by-passed into the aorta by a channel ductus arteriosus

Ductus arteriosus

• Connects the left branch of the pulmonary trunk to arch of aorta(beyond the origin of left subclavian artery)

• It protects the lungs from circulatory overloading.

Pulmonary vascular resistance

• is high in fetal life and pulmonary blood flow is low as the lungs do not need much blood for their survival but developing brain does.

Umbilical arteries

• About 65%of blood in the descending aorta

• Passes into umbilical arteries(right and left)

• Which are direct branches of fetal internal iliac arteries(hypo gastric arteries)

• Remaining 35% of blood supplies the lower half of the body and viscera

Postnatal changes

• Once the child takes the first respiration,pulmonary circulation begins and the right and left hearts become completely independent of each other.

• All the by-pass channels having served their purpose,obliterate.

• Foramen ovale is closed and becomes fossa ovalis in the right atrium

Ligamentum arteriosum

• The ductus arteriosus becomes a fibrous band called ligamentum arteriosum(which has left recurrent laryngeal nerve hooking around)

• (By 96 hours after birth 100% closure occurs)

• Many factors contribute to this process of obliteration called involution(mainly oxygen,and transforming growth factor)

Ligamentum venosum

• Ductus venosus becomes a fibrous band called ligamentum venosum which is seen in continuation with ligamentum teres(obliterated left umbilical vein)

Other changes and clinical aspects

• The umbilical arteries become umbilical ligaments attached to the internal iliac arteries upto superior vesical arteries.

• Any failure of all these closures lead to• Patent foramen ovale,ASD,VSD,PDA and

coarctation of aorta.• The left umbilical vein remains patent for

considerable time and can be used for exchanging transfusions.