Before birth your circulatory system was somewhat different than it is now. The major cause was that before birth your lungs did not contain air and so were not functional.
Instead of acquiring oxygen from the lungs the fetus gets its oxygen and nutrition, and eliminates wastes through the umbilical cord which is connected to the placenta. The placenta is a specialized structure produced by the embryo which grows into the walls of the uterus during embryonic development. The blood vessels of the placenta are in close association with the blood vessels of the uterus, but there is no mixing of blood cells or large molecules. Small molecules such as oxygen, carbon dioxide, and urea freely diffuse across the placenta-uterine junction. Figure 29.1 shows the circulatory system of the unborn child.
Correctly label the anatomical structures in Figure 291-
Blood flows from the placenta through the umbilical vein carrying oxygen and nutrients from the mother to the fetus. The umbilical cord enters the fetus at the umbilicus. At the liver the umbilical vein becomes the ductus venosus which empties into the inferior vena cava. A branch of the umbilical vein joins the hepatic-portal vein to supply the liver, but since the liver is not processing food from the intestines the flow of blood to the liver is not as great as after birth.
Only during the time in the uterus does the right atrium receive oxygenated blood. Since the lungs are nonfunctional, there is little reason for blood to be pumped to the right ventricle and from there to the lungs. Therefore, a hole, the foramen ovale, is present between the right atrium and the left atrium. Oxygenated blood
Figure 29.1 Fetal Circulation
Aorta Ductus arteriosus Ductus venosus Foramen ovale Internal iliac artery Liver Placenta Umbilical artery Umbilical vein Umbilicus can then be pumped to the left ventricle and from there to the body through the aorta.
Some blood does travel into the right ventricle and is then pumped out the pulmonary trunk toward the lungs. Most of the blood in the pulminary trunk is shunted through another special vessel, the ductus arteriosus, from the pulmonary artery into the aorta. Thus, only a very small amount of blood travels into the lungs.
Blood flows out of the aorta into the arteries to all parts of the body. The umbilical arteries are branches of the internal iliac arteries which carry blood from the fetus to the placenta for the elimination of waste and reoxygenation. The umbilical arteries are twisted around the umbilical vein.
At birth the umbilical arteries, umbilical vein, ductus veno-sus, and the ductus arteriosus vasoconstrict, atrophy, and become ligaments. For example, the umbilical vein becomes the round ligament of the liver (see chapter 20) and the ductus arteriosus becomes the ligamentum arteriosum (see chapter 27). Shortly after birth the foramen ovale closes to become the fossa ovalis, a depression in the interatrial septum.
1. _ What structure allows blood to flow between atria in the fetus?
2. __ The ductus arteriosus becomes the (2).
3. _ What color would you expect the blood in the superior part of the inferior vena cava of the fetus to be?
4. _ How many umbilical veins are there?
5. _ Where do the umbilical arteries begin?
6. _ What special structure shunts blood from the pulmo nary artery to the aorta?
7. _ What physiological event prevents the new born baby from losing blood through the cut umbilical cord?
8. _ The umbilical cord enters the body through the _(§)_.
9. _ Who makes the placenta?
10. _ Which blood vessel becomes the round ligament?
Was this article helpful?
The first trimester is very important for the mother and the baby. For most women it is common to find out about their pregnancy after they have missed their menstrual cycle. Since, not all women note their menstrual cycle and dates of intercourse, it may cause slight confusion about the exact date of conception. That is why most women find out that they are pregnant only after one month of pregnancy.