If its lungs aren’t working then how does blood flow go through the fetal heart?
A few days after fertilization takes place in the fallopian tube the embryo migrates to the body of the uterus and implants in its lining. As it burrows in further some of its outer support tissue joins with the lining of the uterus to form the placenta. The placenta is a specialized organ that allows the blood of the mother and the developing fetus to come very close to each other but not intermingle. The blood connection between them comes from the arteries in the lining of the uterus and the baby’s umbilical cord. Due to this set up chemicals can move back and forth between the mother’s and the baby’s circulation. In this way the mother can send her child the oxygen and nutrients it needs to live, grow and develop while taking away metabolic waste.
But the fetus faces a major dilemma because its heart is set up to send the same amount of blood from the left ventricle to the body as it does from the right ventricle to the lungs. But its lungs are closed for business. So now what?
Instead of its lungs providing the oxygen the fetus needs and getting rid of the carbon dioxide it doesn’t need, it’s the placenta that fulfills this role. Blood travels from the left ventricle of the fetal heart to its tissues and also through its umbilical arteries into the placenta. In here the fetal blood comes close to the maternal blood allowing oxygen that her blood just picked up from her lungs to move from it to the fetus and carbon dioxide to move from the fetal blood to the mother. The newly oxygenated fetal blood from the placenta then travels through its umbilical vein back to the right side of its heart.
So the fetus may be getting what it needs from its mother's blood through the placenta but how is its cardiovascular system going to work right if its lungs aren’t working? The job of the right ventricle in your heart is to pump deoxygenated blood that it receives from your tissues to your lungs to pick up a new supply of oxygen and get rid of carbon dioxide and then go back to the left ventricle to be pumped out to the tissues again. But in the fetus, the natural way from the right ventricle to the lungs is mostly barred because it can’t breathe in air while in the womb and so its lungs are closed. If the right ventricle of the fetal heart is set up to send blood to the lungs but the way is mostly barred then how does it send the oxygenated blood it receives from the placenta through the umbilical vein to the tissues through its left ventricle?
To solve this problem the fetal heart has two shunts that allow blood to travel directly from the right to the left side of its heart and its aorta.
As the oxygenated blood from the umbilical vein and the deoxygenated blood from the veins of the lower part of the fetus come toward the right atrium most of it is sent straight over to the left atrium through an opening in the wall between them called the foramen ovale.
The deoxygenated blood that comes into the right atrium from the upper part of the fetus moves into the right ventricle and is pumped into the pulmonary arteries but most of it goes straight into the aorta through a connection called the ductus arteriorus.
It’s these two shunts, the foramen ovale between the right and left atria and the ductus arteriosus between the pulmonary arteries and the aorta that allow most of the fetal blood to bypass its non-functioning lungs and go into its arterial circulation where it can feed the fetal tissues.
Three Questions for Mr. Darwin
- How did life anticipate the need for and from where did the information come to make the umbilical vessels that connect the fetus with the mother’s blood?
- How did life anticipate the need for and from where did the information come to make the foramen ovale so that most of the blood from umbilical vein and the lower part of the fetus going back to the right side of the heart is shunted into the left atrium and from there to the left ventricle so it can be pumped out to the fetal tissues?
- How did life anticipate the need for and from where did the information come to make the ductus arteriosus so that most of the blood that is pumped out of the right ventricle into the pulmonary artery is shunted straight into the aorta so it goes to the fetal tissues?
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Howard Glicksman M. D. graduated from the University of Toronto in 1978. He practiced primary care medicine for almost 25 yrs in Oakville, Ontario and Spring Hill, Florida. He now practices palliative medicine for a Hospice organization in his community. He has a special interest in how the ethos of our culture has been influenced by modern science’s understanding and promotion of what it means to be a human being.
Copyright 2018 Dr. Howard Glicksman. All rights reserved. International copyright secured.
