A 42-year-old female is admitted to the hospital with dyspnea. Imaging reveals severe mitral valve regurgitation. Which of the following structures prevents regurgitation of the mitral valve cusps into the left atrium during systole?

**Core Concept**
The **mitral valve** is a complex structure that ensures blood flows from the **left atrium** to the **left ventricle** during diastole and prevents backflow during systole. The proper functioning of the mitral valve is crucial for maintaining efficient cardiac output.

**Why the Correct Answer is Right**
The correct answer is related to the structure that plays a crucial role in preventing the mitral valve cusps from regurgitating into the left atrium during systole. This structure is the **chordae tendineae**, which are fibrous strings that connect the mitral valve cusps to the **papillary muscles**. During systole, the papillary muscles contract, tightening the chordae tendineae and preventing the mitral valve cusps from prolapsing into the left atrium.

**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect because it does not directly prevent mitral valve regurgitation.
**Option B:** This option is also incorrect as it is not directly involved in the prevention of mitral valve regurgitation.
**Option C:** This choice is incorrect because, although it is part of the mitral valve apparatus, it is not the primary structure that prevents regurgitation.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the **mitral valve apparatus**, including the chordae tendineae and papillary muscles, works together to ensure proper valve function. Damage to any part of this apparatus can lead to mitral regurgitation.

**Correct Answer:** D. Chordae tendineae.

✓ Correct Answer: D. Chordae tendineae