June 15, 2023 Author : José Roquette The fetus circulatory system begins to develop very early, but until birth, blood circulation and oxygen and nutrient differ significantly from what happens afterwards. Before birth : Gas exchange takes place in the placenta, for this process lungs are not functional; The umbilical cord ensures the connection between the placenta and the fetus; Three structures complete the particulars of the fetal circulation – the ductus venosus, the foramen ovale and ductus arteriosis – and make the blood circulation fulfill its functions efficiently during this phase. At birth , the umbilical cord is cut, the lungs begin to function, and everything changes . The placenta and the umbilical cord During pregnancy, the connection between the fetus and the outside environment is provided by the placenta: The placenta develops inside the mother uterus and the fetus depends on this organ to receive oxygen and nutrients from the mother blood, as well as to eliminate carbon dioxide and metabolic waste; The placenta is connected to the fetus by the umbilical cord which contains blood vessels: 2 umbilical arteries and 1 umbilical vein: The umbilical arteries carry blood from the fetus to the placenta, which is poor in oxygen and contains waste to be eliminated; The umbilical vein returns blood rich in oxygen and nutrients to the fetus, essential for its healthy development. Ductus venosus, foramen ovale, and ductus arteriosus Blood with oxygen and nutrients from the umbilical vein must be distributed to all the organs and tissues of the fetus. For this, it is essential that it reaches the heart and aorta. On the other hand, since the lungs are not responsible for gas exchange in the fetus, the pulmonary circulation cannot be overloaded with blood that is not needed. So: Much of the oxygenated blood from the umbilical vein passes through the ductus venosus into the inferior vena cava and enters the right atrium; Once in the right atrium, two other structures make it possible to bypass the pulmonary circulation and non-functioning lungs: The foramen ovale , which maintains communication between the two atria, lets oxygenated blood pass from the right atrium to the left atrium (and from here to the left ventricle and aorta to irrigate the heart, the brain and many other tissues and organs); The ductus arteriosus diverts some blood that enters the pulmonary artery directly into the aorta, preventing it from reaching the lungs. Thus, there is no overload of the lungs of the fetus, only the blood that is sufficient for the maintenance of these organs arrives here. Changes at birth When the baby is born, the umbilical cord is cut and the newborn stops receiving oxygen and nutrients from the mother. With the first breaths, the lungs expand and become responsible for oxygenating the blood . The ductus arteriosus, foramen ovale, and ductus venosus are no longer necessary and, as a rule, close in the early stages of life, a process to which changes in arterial, intracardiac and pulmonary pressure contribute. From birth : In the right heart (right atrium and right ventricle) only non-oxygenated or venous blood circulates; In the left heart (left atrium and left ventricle) only oxygenated or arterial blood circulates. The content published in the Health Guide is intended for the general public and is provided for informational and educational purposes only. It does not replace individual medical assessment, diagnosis, or personalized clinical advice from a qualified healthcare professional. The content is produced or reviewed by physicians and other healthcare professionals at Hospital da Luz and is based on the knowledge available at the time of publication or the most recent update, as indicated at the beginning of each item.
