Question

Which of these statements is correct? a. Fetal circulation, like adult circulation, takes blood equally to a pulmonary circuit and a systemic circuit. b. Fetal circulation shunts blood away from the lungs but makes full use of the systemic circuit. c. Fetal circulation includes exchange of substances between fetal blood and maternal blood at the placenta. d. Unlike adult circulation, fetal blood always carries \(\mathrm{O}_{2}\) -rich blood and therefore has no need for the pulmonary circuit. e. Both b and c are correct.

Short answer

Both b and c are correct.

Step-by-step solution

Statement a

Fetal circulation, like adult circulation, takes blood equally to a pulmonary circuit and a systemic circuit. This statement implies that fetal circulation is the same as adult circulation. However, that's not the case. In the fetus, blood flows differently, and the lungs are nonfunctional until birth. So, this statement is incorrect.

Statement b

Fetal circulation shunts blood away from the lungs but makes full use of the systemic circuit. This statement implies that fetal circulation allows blood to bypass the lungs, which is true. In the fetus, blood bypasses the lungs through some specific structures called the foramen ovale, and the ductus arteriosus allowing blood to bypass the pulmonary circulation. This helps in making full use of the systemic circuit. So this statement is correct.

Statement c

Fetal circulation includes the exchange of substances between fetal blood and maternal blood at the placenta. In fetal circulation, the placenta is the primary site for the exchange of nutrients, oxygen, and waste products between the mother and the fetus. Without the placenta, the fetus would not receive the necessary nutrients and oxygen required to survive and grow. So, this statement is also correct.

Statement d

Unlike adult circulation, fetal blood always carries \(\mathrm{O}_{2}\)-rich blood and therefore has no need for the pulmonary circuit. Although it's true that fetal blood has higher oxygen content than adult blood because of the presence of fetal hemoglobin, the fetal circulation does partially use deoxygenated blood, which would eventually mix with oxygenated blood to supply the fetus. However, it doesn't mean the fetus has no need for the pulmonary circuit. The statement is misleading and is incorrect.

Statement e

Both b and c are correct. We have established that both statements b and c are correct, which means statement e is also correct. The correct answer is: \e Both b and c are correct.

Key concepts

Pulmonary Circuit

The pulmonary circuit plays a substantial role in adult circulation. It's responsible for transporting blood from the heart to the lungs for oxygenation and then back to the heart. However, in fetal circulation, this circuit operates differently.
During fetal development, the lungs aren't used for breathing as they are filled with fluid rather than air. Instead, oxygen is obtained from the mother's blood via the placenta. To bypass the lungs, the fetal circulation features specialized structures like the foramen ovale and ductus arteriosus:

• The foramen ovale is an opening between the right and left atria. It allows blood to flow directly from the right atrium to the left atrium, thus bypassing the lungs.
• The ductus arteriosus connects the pulmonary artery to the aorta, further allowing blood to bypass the pulmonary circuit directly.

This unique setup ensures that while the pulmonary circuit is present, it is not fully utilized in the fetal stage, unlike adult circulation.

Systemic Circuit

The systemic circuit in both fetal and adult circulation is crucial for distributing oxygenated blood to the rest of the body. In adults, blood that has been oxygenated in the lungs travels through the aorta to the systemic circuit where it delivers oxygen and nutrients to tissues.
In the fetus, the systemic circuit is fully utilized as the blood bypasses the lungs and still needs to be distributed to various parts of the body. Blood returns from the placenta, rich with oxygen and nutrients, and flows into the right side of the heart. Then, through mechanisms like the foramen ovale and ductus arteriosus, it is rerouted into the left side of the heart and subsequently into the systemic circuit.
This system allows the fetus to grow and develop effectively by ensuring that critical tissues receive enough oxygen and nutrients despite not using the lungs for oxygen exchange.

Placenta

The placenta is a vital organ during pregnancy, acting as the lifeline between the mother and the fetus. It plays a crucial role in fetal development by facilitating the exchange of oxygen, nutrients, and waste products between maternal and fetal blood.
The placenta attaches to the wall of the uterus, and the umbilical cord stemming from the fetus connects to it. The fetal blood and the maternal blood do not mix, but nutrients and oxygen from the mother pass across the placenta to the fetus. Waste products from fetal blood are transferred back to the mother's blood for elimination.

• Oxygen-rich blood from the placenta travels through the umbilical vein into the fetus, ensuring the developing baby receives oxygen and essential nutrients.
• Nutrient exchange supports fetal growth, enabling cells to function and proliferate.
• Waste exchange allows carbon dioxide and other metabolic waste products to be removed from the fetal body.

This exchange is essential because the placenta serves as the fetus's lungs, kidneys, and digestive system until birth.