Question

Which of the following INCORRECTLY pairs the fetal circulation shunt with its function? A. Ductus venosus-bypasses the liver B. Ductus venosus-bypasses the pulmonary veins C. Ductus arteriosus-directs blood from the pulmonary artery to the aorta D. Ductus arteriosus-prevents blood from entering the lungs

Short answer

B. Ductus venosus-bypasses the pulmonary veins

Step-by-step solution

Understanding Fetal Circulation Shunts

Identify and understand the role of the different shunts in fetal circulation: ductus venosus, foramen ovale, and ductus arteriosus.

Role of Ductus Venosus

The ductus venosus shunt bypasses the liver, allowing oxygenated blood from the umbilical vein to flow directly into the inferior vena cava.

Role of Foramen Ovale

The foramen ovale allows blood to bypass the non-functional fetal lungs by moving blood directly from the right atrium to the left atrium.

Role of Ductus Arteriosus

The ductus arteriosus directs blood from the pulmonary artery to the aorta, diverting blood away from the fetal lungs.

Identify the Incorrect Pair

Review the answer choices to identify the one that incorrectly pairs a shunt with its function: - A. Ductus venosus-bypasses the liver - B. Ductus venosus-bypasses the pulmonary veins - C. Ductus arteriosus-directs blood from the pulmonary artery to the aorta - D. Ductus arteriosus-prevents blood from entering the lungs. Given the roles described, the ductus venosus does not bypass the pulmonary veins.

Key concepts

Ductus Venosus

The ductus venosus is a crucial part of fetal circulation. It is a blood vessel that connects the umbilical vein to the inferior vena cava. This connection allows oxygenated blood from the placenta to bypass the liver, ensuring that the most oxygen-rich blood is delivered directly to the heart.

In fetal development, the liver is not fully functional and requires only a small amount of the oxygenated blood. The primary purpose of the ductus venosus is to prioritize the flow of oxygenated blood to vital organs.

Once the baby is born and starts breathing, the ductus venosus closes and eventually becomes a ligament.

Foramen Ovale

The foramen ovale is another key component of fetal circulation. It is an opening between the right and left atria of the fetal heart.

This opening allows blood to skip the non-functional fetal lungs.

Normally, blood would travel to the lungs to get oxygenated. However, since the fetus gets oxygen from the mother via the placenta, the foramen ovale ensures efficient blood flow directly from the right atrium to the left atrium.

After birth, the baby's lungs take over the task of oxygenating blood, and the foramen ovale typically closes within the first few days of life.

Ductus Arteriosus

The ductus arteriosus is an important shunt in fetal circulation. It connects the pulmonary artery to the aorta.

This vessel allows blood to bypass the lungs, where it would otherwise circulate before being delivered to the rest of the body. Since the fetal lungs are not used for gas exchange and are filled with fluid, the ductus arteriosus ensures that blood flows directly into the aorta and then to the rest of the body.

When the baby is born and begins to breathe, the lungs expand and the ductus arteriosus normally closes within the first few days of life, redirecting blood through the now functional lungs.

Shunts in Fetal Circulation

Fetal circulation relies on several shunts to ensure efficient blood flow. These shunts include the ductus venosus, foramen ovale, and ductus arteriosus.

• The ductus venosus directs oxygenated blood from the placenta to the heart, bypassing the liver.
• The foramen ovale allows blood to move between the atria, bypassing the lungs.
• The ductus arteriosus connects the pulmonary artery to the aorta, further bypassing the lungs.

These shunts are vital for fetal development and function effectively until birth. After birth, with the baby's lungs taking over the role of oxygenation, the shunts close and the circulatory system adapts to postnatal life.