Which ONE of the following statements regarding the right atrium of the heart is CORRECT?Group of answer choicesIts opening into the right ventricle is guarded by the tricuspid valveIt receives de-oxygenated blood from the pulmonary veinsIt receives de-oxygenated blood via pulmonary arteriesIt forms the base of the heart between the superior and inferior venae cavaeThe ligamentum arteriosium is a remnant of the fetal circulation that is associated with it

Let's go through each statement one by one:

1. "Its opening into the right ventricle is guarded by the tricuspid valve" - This statement is CORRECT. The tricuspid valve is located between the right atrium and the right ventricle, and it prevents backflow of blood from the right ventricle into the right atrium.

2. "It receives de-oxygenated blood from the pulmonary veins" - This statement is INCORRECT. The right atrium receives deoxygenated blood from the body through the superior and inferior vena cava, not from the pulmonary veins. The pulmonary veins carry oxygenated blood from the lungs to the left atrium.

3. "It receives de-oxygenated blood via pulmonary arteries" - This statement is INCORRECT. The right atrium does not receive blood from the pulmonary arteries. The pulmonary arteries carry deoxygenated blood from the right ventricle to the lungs.

4. "It forms the base of the heart between the superior and inferior venae cavae" - This statement is INCORRECT. The base of the heart is formed by the left atrium, not the right atrium.

5. "The ligamentum arteriosum is a remnant of the fetal circulation that is associated with it" - This statement is INCORRECT. The ligamentum arteriosum is a remnant of the ductus arteriosus, which is a part of the fetal circulation that bypasses the lungs. It is not associated with the right atrium.

So, the correct answer is: "Its opening into the right ventricle is guarded by the tricuspid valve".