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The superpower of the placenta: How to allow the fetus to obtain oxygen and nutrients in the mother's body?
The human circulatory system is different before and after birth. The fetal circulatory system consists of the placenta, umbilical vessels wrapped in the umbilical cord, the heart, and blood vessels throughout the body. One major difference between the fetal circulation and the postnatal circulation is that the lungs are not used during the fetal stage, so various shunts exist to carry oxygenated blood and nutrients from the placenta to fetal tissues.
The placenta has incredible functions as a nutrient and waste exchange station between mother and fetus.
Exchange of oxygen, nutrients and waste
The placenta is the place of exchange between the maternal and fetal cycles. Essential elements such as water, glucose, amino acids and vitamins and oxygen diffuse freely through the placenta. The two umbilical arteries carry systemic arterial blood from the fetus to the placenta, where waste is exchanged and oxygen and nutrients are obtained.
Fetal oxygen transport
Hemoglobin is a structure found in red blood cells that binds and carries oxygen. Fetal hemoglobin enables the fetus to better extract oxygen from the placenta, and its molecule is composed of two alpha chains and two gamma chains (2α2γ). This leftward shift in the oxygen-hemoglobin dissociation curve makes it easier to absorb oxygen at relatively low oxygen concentrations. This also allows fetal hemoglobin to absorb oxygen from adult hemoglobin, especially in the placenta, which is more efficient when oxygen pressure is lower than in the lungs.
Before birth
Oxygenated blood transported by the placenta flows into the fetal inferior vena cava (IVC) through the umbilical vein, and then enters the heart via the ductus venosus or the liver. When oxygenated blood enters the IVC, it flows parallel to the deoxygenated blood from fetal systemic veins, forming a double-layer blood flow. The right atrium of the heart has a special structure, the foramen ovale, which is a channel that drains oxygenated blood from the right atrium to the left atrium, helping to prevent blood from being directed into the undeveloped lungs.
During the fetal stage, the lungs fill with fluid and remain collapsed because the fetus is inside the amniotic sac and the placenta provides the oxygen it needs.
After birth
When the umbilical cord is severed and the baby begins to breathe, the source of oxygen changes, prompting a shift from the fetal circulation to the postpartum circulation. As the baby breathes, the lungs expand and fill with oxygen, which reduces the resistance of the pulmonary artery and promotes blood flow from the right ventricle to the lungs, thereby establishing the baby's pulmonary circulation. As blood flow increases, pressure in the left atrium gradually exceeds that in the right atrium, closing the foramen ovale.
Potential complications
It is important to note that not all babies' cyclic transitions proceed as described above. Premature infants may lack sufficient surfactant due to immature lungs, which prevents the alveoli from maintaining their openings, resulting in failure to reduce pulmonary vascular resistance, resulting in respiratory distress syndrome. In addition, during delivery, the baby may inhale meconium, causing airway obstruction and further affecting normal lung function.
Remnants of the fetal circulation may still exist in the adult body, which makes the physiological characteristics of the fetal period still affect the acquired health to some extent.
Conclusion
The unique function of the placenta lies in how successfully it ensures that the fetus receives oxygen and vital nutrients and maintains healthy functioning during the earliest stages of life. With the continuous advancement of technology and science, people's research on the placenta is still in-depth. Perhaps in the future we will be able to understand more related physiological secrets and potential application directions. Could the placenta become a breakthrough in our life medicine?
