## **Core Concept**
The bronchopulmonary segment, also known as a lung segment, is a distinct subdivision of the lung defined by its own bronchus and arterial supply. It is a functional unit of the lung, and its anatomy is crucial for understanding respiratory diseases and surgical interventions. The lung is divided into lobes, and each lobe is further divided into bronchopulmonary segments.

## **Why the Correct Answer is Right**
The correct answer states that a bronchopulmonary segment is supplied by a segmental bronchus and a branch of the pulmonary artery, and it drains into the pulmonary veins. This is accurate because each bronchopulmonary segment receives its own air supply from a segmental bronchus and its own blood supply from a branch of the pulmonary artery. The pulmonary veins, however, run between the lobules and segments, collecting blood from multiple segments.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option might suggest that a bronchopulmonary segment is defined solely by its bronchus or only by its arterial supply, which is incomplete.
- **Option B:** This could imply that the segment's venous drainage is segmental, which is not accurate. The pulmonary veins drain multiple segments.
- **Option C:** If this option suggests that segments are not separated by connective tissue, it would be incorrect. Segments are indeed separated by connective tissue.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the lung's segmental anatomy is critical for surgical resections, such as segmentectomies, and for understanding the spread of diseases like pneumonia or tuberculosis, which often respect segmental boundaries.

## **Correct Answer:** D. Each lung has 10 bronchopulmonary segments.