Foetal circulation?

Fetal circulation refers to the circulation of blood in a developing fetus. It is different from the circulation in adults due to the presence of certain structures that allow the fetus to receive oxygen and nutrients from the mother's blood supply.

In fetal circulation, oxygenated blood from the placenta enters the fetus through the umbilical vein. This blood then bypasses the liver through a structure called the ductus venosus and enters the inferior vena cava. From the inferior vena cava, the blood is directed to the right atrium of the heart.

In the right atrium, the blood mixes with deoxygenated blood returning from the upper body. It then passes through the foramen ovale, a hole in the atrial septum, which allows most of the blood to bypass the right ventricle and enter the left atrium. From the left atrium, the blood enters the left ventricle and is pumped out to the body through the aorta.

A small portion of the blood in the right atrium does enter the right ventricle and is pumped to the lungs. However, the majority of the blood in the pulmonary artery is directed away from the lungs through a vessel called the ductus arteriosus. This vessel connects the pulmonary artery to the descending aorta, allowing blood to bypass the lungs and flow directly to the lower body.

After birth, several changes occur in the circulatory system to transition from fetal to adult circulation. The foramen ovale closes, the ductus arteriosus constricts and eventually closes, and the umbilical vessels are no longer needed. These changes ensure that blood is properly oxygenated in the lungs and flows through the heart in the adult circulation pattern.