Fetal Blood: Circulation Diagram & Concept

Fetal Blood: Circulation Diagram & Concept
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  • 0:00 Overview of Fetal Circulation
  • 0:35 Role of the Placenta
  • 1:20 Pathway of Blood
  • 3:05 Closing the Holes
  • 3:50 Lesson Summary
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Lesson Transcript
Instructor: Shannon Compton

Shannon teaches Microbiology and has a Master's and a PhD in Biomedical Science. She also researches cancer and neurodegenerative diseases.

Have you ever wondered how a fetus gets oxygen in the womb, which is an aquatic environment? The answer lies in the way a fetus's circulatory system differs from that of an organism outside the womb. This lesson covers fetal blood and circulation.

Overview of Fetal Circulation

Have you ever wondered how a fetus gets oxygen in the womb? The answer to that question is that a fetus in the womb gets oxygen from its mother. Technically, the placenta acts like lungs for the fetus. Deoxygenated blood from the fetus travels through the umbilicus, or navel, to the placenta. This blood also carries fetal waste products. In the placenta, waste products leave the fetal blood and are picked up by the maternal blood. Oxygen in the maternal blood is transferred to the fetal blood at the same time. The oxygenated blood then leaves the placenta and travels back to the fetus through the umbilicus.

This image shows the orientation of a fetus, the placenta, and the womb
Image of a placenta and fetus

Role of the Placenta

The mother's circulation is separate from that of the fetus. So, how does oxygen get from the maternal blood to the fetal blood?

Fetal hemoglobin, the protein that binds oxygen in the blood, has a higher affinity for oxygen than does maternal hemoglobin. This means that a fetus can steal oxygen from its mother's blood. Also, water, glucose, amino acids, vitamins, and inorganic salts freely diffuse across the placenta along with oxygen. A structure called the chorionic villus is the actual site of oxygen, waste, and nutrient exchange. It has an alveolus-like structure, which is the same structure as lungs.

Pathway of Blood

The umbilical vein carries blood from the placenta to the fetus. Even though this is called a vein, it actually carries oxygen-rich blood. Some of this blood passes through an opening called the fetal ductus venosus and enters the inferior vena cava. The inferior vena cava is a vessel that takes blood to the fetal heart. The rest of the blood enters the fetal liver through a vessel called 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 called the foramen ovale. Most of the blood flows through this hole directly into the left atrium from the right atrium. Fetal blood does not travel through the lungs because of this hole between the atria. The fetal blood travels from the left atrium to the left ventricle. Then it is pumped through the aorta, or the largest artery, into the body. Once the blood has lost much of its oxygen and picked up waste from the fetus it returns to the placenta. The umbilical arteries are responsible for taking oxygen-poor blood and waste back to the placenta.

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