Why does blood bypass the lungs in a fetus

The blood is bluish in colour because it is low in oxygen. When the heart relaxes, the blood flows through the tricuspid valve into the right ventricle.

The right ventricle contracts to send the blood through the pulmonary valve into the pulmonary arteries. The blood travels to the lungs, where it gets fresh oxygen and turns bright red again. It returns to the left atrium through the pulmonary veins. Then it moves through the mitral valve to the left ventricle.

The left ventricle pumps blood high in oxygen out through the aortic valve into the aorta. The aorta delivers the blood to the body and the process begins again. This happens in two ways:. 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. Most of the blood that leaves the right ventricle in the fetus bypasses the lungs through the second of the two extra fetal connections known as the ductus arteriosus. The fetal circulatory system uses two right to left shunts, which are small passages that direct blood that needs to be oxygenated. The purpose of these shunts is to bypass certain body parts?

The shunts that bypass the lungs are called the foramen ovale, which moves blood from the right atrium of the heart to the left atrium, and the ductus arteriosus, which moves blood from the pulmonary artery to the aorta. Oxygen and nutrients from the mother's blood are transferred across the placenta to the fetus. The enriched blood flows through the umbilical cord to the liver and splits into three branches.

The blood then reaches the inferior vena cava, a major vein connected to the heart. Most of this blood is sent through the ductus venosus, also a shunt that passes highly oxygenated blood through the liver to the inferior vena cava and then to the right atrium of the heart. A small amount of this blood goes directly to the liver to give it the oxygen and nutrients it needs. The fetus gets life support from the mother through the placenta.

Waste products and carbon dioxide from the fetus are sent back through the umbilical cord and placenta to the mother's circulation to be removed. Click to Enlarge. 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.