Why does fetal circulation bypass the liver

Conversely, there are certain cyanotic congenital heart defects for example, transposition of the great vessels in which the circulatory system allows little or no deoxygenated blood delivery to the lungs.

As a result, little or no oxygenated blood can be delivered systemically, causing cyanosis in peripheral tissues. In this case, therapeutically maintaining a patent ductus arteriosus allows some mixing of oxygenated and deoxygenated blood, allowing some amount of oxygenated blood into systemic circulation, which can assist in decreasing the severity of cyanosis in affected infants.

To accomplish this, prostaglandin E1 may be administered to maintain patency of the ductus arteriosus until surgical correction of the underlying heart defect can be performed. Kiserud T,Stratford L,Hanson MA, Umbilical flow distribution to the liver and the ductus venosus: an in vitro investigation of the fluid dynamic mechanisms in the fetal sheep. American journal of obstetrics and gynecology. The Journal of obstetrics and gynaecology of the British Empire.

Clinics in perinatology. Committee Opinion No. Obstetrics and gynecology. Clinical case reports. Birth defects research. Part A, Clinical and molecular teratology. Ferguson JM, Pharmacotherapy for patent ductus arteriosus closure. Congenital heart disease. The Cochrane database of systematic reviews. Embryology, Fetal Circulation. Free Review Questions.

Introduction Fetal circulation differs from adult circulation in a variety of ways to support the unique physiologic needs of a developing fetus. Development Once there is adequate fetal-placental circulation established, blood transports between fetus and placenta through the umbilical cord containing two umbilical arteries and one umbilical vein. The structural changes that occur to each structure are as follows: Umbilical arteries: Discontinuation of placental blood flow, and subsequent fall in pressure, causes occlusion of the umbilical arteries a few minutes following delivery.

Full occlusion of the distal arteries occurs in the months following birth. Once fully occluded, the distal portions of the former umbilical arteries become the medial umbilical ligaments, found on the anterior abdominal wall. The proximal portions of the former umbilical arteries remain open as the superior vesical arteries. Umbilical vein: This vessel remains open for some time after birth, allowing a final volume of blood of approximately mL to flow from the placenta into the infant prior to occlusion.

Eventually, the umbilical vein also obliterates, forming the ligamentum hepatis teres, which is the lower portion of the falciform ligament, which remains intra-abdominally into adulthood as a fibrous connection between the anterior surface of the liver and the anterior abdominal wall. Ductus venosus: At birth, the ductus venosus collapses.

Over time, it obliterates into a ligament termed the ligamentum venosus, a fibrous remnant coursing from the ligamentum hepatis teres to the inferior vena cava. Foramen ovale: Initiation of respiration opens the pulmonary circulation and lowers dramatically the pulmonary arterial pressure and hence the right atrial pressure. Because of the dramatic increase in pulmonary blood flow, the left atrial pressure increases. Blood preferentially enters the path of least resistance; in the fetus, this path was the ductus arteriosus.

In an infant immediately following delivery, lower pressure in the lungs means that lung vasculature has become the new path of least resistance, and the majority of blood will now enter the pulmonary arteries and circulate through the lung vasculature.

Subsequently, within the atrial septum, the septum primum is pushed against the septum secundum. Over time, this leads to fusion of the two septa and therefore closure of the foramen ovale. The resulting layer of tissue which completely closes the foramen ovale is termed the fossa ovalis, and it is visible into adulthood as a depression within the septum of the right atrium.

Ductus arteriosus: Closure of the ductus arteriosus occurs almost immediately following birth. In response to initial respiration, bradykinin gets released from the lungs.

When blood goes through the placenta it picks up oxygen. The oxygen rich blood then returns to the fetus via the third vessel in the umbilical cord umbilical vein. The oxygen rich blood that enters the fetus passes through the fetal liver and enters the right side of the heart. The oxygen rich blood goes through one of the two extra connections in the fetal heart that will close after the baby is born.

The hole between the top two heart chambers right and left atrium is called a patent foramen ovale PFO. This hole allows the oxygen rich blood to go from the right atrium to left atrium and then to the left ventricle and out the aorta.

As a result the blood with the most oxygen gets to the brain. The fetal circulatory system uses 3 shunts. These are small passages that direct blood that needs to be oxygenated. The purpose of these shunts is to bypass the lungs and liver. That's because these organs will not work fully until after birth. The shunt that bypasses the lungs is called the foramen ovale. This shunt moves blood from the right atrium of the heart to the left atrium.

The ductus arteriosus moves blood from the pulmonary artery to the aorta. Oxygen and nutrients from the mother's blood are sent across the placenta to the fetus. The enriched blood flows through the umbilical cord to the liver and splits into 3 branches. The blood then reaches the inferior vena cava.

This is a major vein connected to the heart. Most of this blood is sent through the ductus venosus. This is also a shunt that lets highly oxygenated blood bypass the liver to the inferior vena cava and then to the right atrium of the heart.

A small amount of this blood goes straight to the liver to give it the oxygen and nutrients it needs. Waste products from the fetal blood are transferred back across the placenta to the mother's blood. Blood enters the right atrium.