16 Questions
What is the primary source of oxygen for a fetus?
Maternal placenta
Why does the fetal circulation have important differences from adult circulation?
Due to the placenta being the oxygen source
What is the function of the placenta in the fetal circulation?
Performing the functions of the lungs, liver, and kidneys
In the fetal circulation, what is the role of the umbilical vein?
Carrying oxygenated blood from the placenta
What occurs in the pulmonary circulation in adults?
Deoxygenated blood is pumped to the lungs for oxygenation
What is the primary difference between fetal and adult circulation?
The source of oxygen
What is the direction of fetal waste flow through the umbilical arteries?
From fetal blood to maternal blood
Why are circulatory shunts present in the fetal circulation?
To direct oxygenated blood to the heart and brain
What is a characteristic of fetal blood flow?
It is relatively low in oxygen
What is the purpose of the ductus venosus and foramen ovale in fetal circulation?
To bypass the liver and lungs
What is the approximate PO2 of fetal blood leaving the placenta?
40 mm Hg
What is the difference in oxygen affinity between HbA and HbF?
HbF has a higher oxygen affinity than HbA
What percentage of oxygen saturation is fetal hemoglobin at a PO2 of 40 mm Hg?
80%-85%
Why is it important for HbF to have a higher oxygen affinity than HbA?
So the fetus can extract maximal oxygen from placental blood
What is the purpose of the umbilical vein in fetal circulation?
To deliver oxygen to the fetus
What is unique about the placenta's anatomical structure?
It is designed to prevent mixing of maternal and fetal blood
Study Notes
Fetal Circulation
- Legally, a person's life begins on the day they are born, but physiologically, they have been alive for several months before birth.
- Fetal circulation is more complicated than in adults because the placenta performs the functions of the lungs, gastrointestinal tract, liver, and kidneys for the growing fetus.
Source of Oxygen
- The most important difference between fetal and adult circulations is the source of oxygen.
- In the fetus, the placenta is the oxygen source, while in adults, oxygenation occurs in the lungs.
Fetal Circulation vs. Adult Circulation
- In adults, deoxygenated blood is pumped from the right heart to the lungs for oxygenation before returning to the left heart.
- In contrast, in the fetus, the maternal placenta delivers oxygenated blood to the fetus, which then bypasses the liver and lungs.
Anatomical Differences
- The placenta is designed to allow oxygen, nutrients, and other maternally borne molecules to diffuse into the fetal blood, while fetal wastes flow in the opposite direction.
- Two structures exist to bypass the pulmonary circulation: the foramen ovale and the ductus arteriosus.
Hemoglobin Types: HbA vs. HbF
- Fetal hemoglobin (HbF) has a higher affinity for oxygen than adult hemoglobin (HbA).
- This allows the fetus to extract maximal oxygen from placental blood, even at low oxygen levels (approximately 40 mm Hg).
- HbF is 80%-85% saturated at this PO2, while HbA is only 75% saturated.
Vascular Shunts in Fetal Circulation
- Three fetal blood vessels (umbilical vein and two umbilical arteries) facilitate the circulation of oxygenated blood from the placenta to the fetus and deoxygenated blood from the fetus back to the placenta.
Learn about the circulatory system of a fetus, from the placenta to the fetal tissues and back. Understand the physiology of fetal circulation and its importance.
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