Blood from the placenta is carried to the fetus by the umbilical vein. In humans, less than a third of this enters the<unk>  ductus venosus and is carried to the inferior vena cava, while the rest enters the liver proper from the inferior border of the liver. The branch of the umbilical vein that supplies the right lobe of the liver first joins with the portal vein. The blood then moves to the right atrium of the heart. In the fetus, there is an opening between the right and left atrium (the foramen ovale), and most of the blood flows through here directly into the left atrium from the right atrium, thus bypassing pulmonary circulation. The continuation of this blood flow is into the left ventricle, and from there it is pumped through the aorta into the body. Some of the blood moves from the aorta through the internal iliac arteries to the umbilical arteries, and re-enters the placenta, where carbon dioxide and other waste products from the fetus are taken up and enter the maternal circulation. Some of the blood entering the right atrium does not pass directly to the left atrium through the foramen ovale, but enters the right ventricle and is pumped into the pulmonary artery. In the fetus, there is a special connection between the pulmonary artery and the aorta, called the ductus arteriosus, which directs most of this blood away from the lungs (which are not being used for respiration at this point as the fetus is suspended in amniotic fluid). Placenta The circulatory system of the mother is not directly connected to that of the fetus, so the placenta functions as the respiratory center for the fetus as well as a site of filtration for plasma nutrients and wastes. Water, glucose, amino acids, vitamins, and inorganic salts freely diffuse across the placenta along with oxygen. The uterine arteries carry blood to the placenta, and the blood permeates the sponge-like material there. Oxygen then diffuses from the placenta to the chorionic villus, an alveolus-like structure, where it is then carried to the umbilical vein. File:circulatory_system_fetus_SMIL.link=|Animated schematic of the hearts and circulatory systems of a fetus and its mother – red and blue represent oxygenated and deoxygenated blood, respectively (animation) Before birth Diagram of the human<unk>  circulatory system. The circulatory system, consisting of the heart, blood vessels, and blood forms relatively early during embryonic development, and continues to develop in complexity within the growing fetus. A functional circulatory system is a biological necessity, since mammalian tissues can not grow more than a few cell layers thick without an active blood supply. The prenatal circulation of blood is different than the postnatal circulation, mainly because the lungs are not in use. The fetus obtains oxygen and nutrients from the mother through the placenta and the umbilical cord. Blood from the placenta is carried to the fetus by the umbilical vein. About half of this enters the<unk>  ductus venosus and is carried to the inferior vena cava, while the other half enters the liver proper from the inferior border of the liver. The branch of the umbilical vein that supplies the right lobe of the liver first joins with the portal vein. The blood then moves to the right atrium of the heart. In the fetus, there is an opening between the right and left atrium (the foramen ovale), and most of the blood flows from the right into the left atrium, thus bypassing pulmonary circulation. The majority of blood flow is into the left ventricle from where it is pumped through the aorta into the body. Some of the blood moves from the aorta through the internal iliac arteries to the umbilical arteries, and re-enters the placenta, where carbon dioxide and other waste products from the fetus are taken up and enter the woman's circulation. Some of the blood from the right atrium does not enter the left atrium, but enters the right ventricle and is pumped into the pulmonary artery. In the fetus, there is a special connection between the pulmonary artery and the aorta, called the ductus arteriosus, which directs most of this blood away from the lungs (which aren't being used for respiration at this point as the fetus is suspended in amniotic fluid). After birth At birth, when the infant breathes for the first time, there is a decrease in the resistance in the pulmonary vasculature. As a result, a higher proportion of the output from the right ventricle flows into the lungs compared to the ductus arteriosus. Consequently, the pressure in the left atrium to increase relative to the pressure in the right atrium. This leads to the closure of the foramen ovale, which is then referred to as the fossa ovalis. Additionally, the increase in the concentration of oxygen in the blood leads to a decrease in prostaglandins, causing closure of the ductus arteriosus. These closures prevent blood from bypassing pulmonary circulation, and therefore allow the neonate's blood to become oxygenated in the newly operational lungs. Sometimes these postnatal closures are incomplete or absent. The vessels or cross-connections remain open (patent), leading to the following conditions: * Patent foramen ovale in the heart * Patent ductus arteriosus in the great vessels * Patent ductus venosus in the great vessels Adult remnants Remnants of the<unk>  can be found in the adult.<unk>  Develops foramen ovale fossa ovalis ductus arteriosus ligamentum arteriosum extra-hepatic portion of the<unk>  left umbilical vein ligamentum teres hepatis("round ligament of the liver") intra-hepatic portion of the<unk>  left umbilical vein(ductus venosus) ligamentum venosum proximal portions of the<unk>  left and right umbilical arteries umbilical branches of the internal iliac arteries distal portions of the<unk>  left and right umbilical arteries umbilical ligaments In addition to differences in circulation, the developing fetus also employs a different type of oxygen transport molecule in its hemoglobin from that when it is born and breathing its own oxygen.<unk>  hemoglobin enhances the fetus' ability to draw oxygen from the placenta. Its oxygen-hemoglobin dissociation curve is shifted to the left, meaning that it is able to absorb oxygen at lower concentrations than adult hemoglobin. This enables<unk>  hemoglobin to absorb oxygen from adult hemoglobin in the placenta, where the oxygen pressure is lower than at the lungs. Until around six months' old, the human infant's hemoglobin molecule is made up of two alpha and two gamma chains (2α2γ). The gamma chains are gradually replaced by beta chains until the molecule becomes hemoglobin A with its two alpha and two beta chains (2α2β).
Fetal circulation
Cardiac cycle
Fetal movement
Cardiovascular physiology
Hemodynamics
Fetal viability
Coronary circulation
Amniotic fluid index