Study the following statements with respect to human cardiovascular system and choose the correct one.

Options

A. All the openings that allow the flow of deoxygenated blood into right atrium are guarded by valves whereas the openings of pulmonary veins have no valves
B. 'AVN' is seen in the lower right corner of the right atrium postero inferior region of the inter atrial septum
C. The semilunar valves of aortic arches are closed during ventricular filling.
D. Tricuspid and bicuspid valves are inter connected by chordae tendineae

Answer

To solve the question regarding the human cardiovascular system, we will analyze each statement provided in the options and determine which one is correct.

### Step-by-Step Solution:

1. **Analyze the First Option:**
- The statement claims that all openings allowing deoxygenated blood into the right atrium are guarded by valves, while the openings of the pulmonary veins have no valves.
- **Evaluation:** This statement is incorrect because the openings of the superior and inferior vena cavae (which carry deoxygenated blood into the right atrium) do not have valves. Additionally, the pulmonary veins (which carry oxygenated blood into the left atrium) also do not have valves. Thus, this option is wrong.

2. **Analyze the Second Option:**
- The statement claims that the Atrioventricular Node (AVN) is located in the lower right corner of the right atrium, specifically in the posterior inferior region of the interatrial septum.
- **Evaluation:** This statement is also incorrect. The AVN is located in the lower part of the right atrium but is not specifically in the lower right corner; it is situated near the interatrial septum. Therefore, this option is wrong.

3. **Analyze the Third Option:**
- The statement claims that the semilunar valves of the aortic arch are closed during ventricular filling.
- **Evaluation:** This statement is correct. During ventricular filling, the ventricles are relaxed, and the semilunar valves (aortic and pulmonary) are indeed closed to prevent backflow of blood into the ventricles. Therefore, this option is correct.

4. **Analyze the Fourth Option:**
- The statement claims that the tricuspid and bicuspid valves are interconnected by a chordae tendineae.
- **Evaluation:** This statement is incorrect. The tricuspid and bicuspid (mitral) valves are not interconnected by chordae tendineae; rather, they are connected to papillary muscles via chordae tendineae. Therefore, this option is wrong.

### Conclusion:
After analyzing all the options, the correct statement regarding the human cardiovascular system is the third option: "The semilunar valves of the aortic arches are closed during ventricular filling."