Which of the following structures allows blood to pass from the left atrium to the right atrium in the foetal circulation?

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Question restatement: Which of the following structures allows blood to pass from the left atrium to the right atrium in the foetal circulation? The answer options are: ligaments arteriosum, Foramen ovale, ductus arteriosus, and ductus venosus.

Option 1: ligamento arteriosum (ligamentum arteriosum). This structure is the fibrous remnant of the ductus arteriosus after birth, and it does not function as a shunt in fetal life. It would not provide a route for blood to move between the atria, so this is incorrect for the question’s intent.

Option 2: Foramen ovale. The foramen ovale is the fetal interatrial opening that facilitates shunting of blood between the right atrium and the left atrium. In fetal circulation, blood tends to flow from the right atrium to the left atrium due to pressure differences, effectively bypassing the nonfunctional fetal lungs. Although the question states left-to-right movement, the established physiological role of the foramen ovale is a right-to-left shunt (right atrium to left atrium). Given the provided answer key lists Foramen ovale, this option is identified as correct in that context. The key physiological mechanism is (right-to-left shunting) via the foramen ovale.

Option 3: ductus arteriosus. This vessel connects the pulmonary artery to the descending aorta, allowing blood to bypass the lungs by flowing from the pulmonary trunk into the aorta. It is not an interatrial shunt and does not connect the atria, so it is not the correct structure for interatrial passage.

Option 4: ductus venosus. This vessel bypasses hepatic circulation by shunting a portion of umbilical vein blood directly to the inferior vena cava. It operates outside the atrial interface and does not create an interatrial passage, making it unrelated to left-to-right atrial flow.

In summary, the foramen ovale is the interatrial channel responsible for allowing blood to pass between the atria in fetal life (typically from right to left), by-passing the lungs. The other three options do not provide an interatrial passage and thus do not fulfill the described function. The question’s stated direction (left to right) conflicts with the established fetal physiology for the foramen ovale, but the option identified as correct corresponds to the fetal shunt between atria.

Anatomy and Physiology Systems II (1017MSC_NA_3255)

Which of the following structures allows blood to pass from the left atrium to the right atrium in the foetal circulation?

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