**Question:** Sequestered lung is supplied most commonly by which pulmonary artery?

**Core Concept:** Sequestrated lung refers to a portion of lung that is separated from the rest of the lung and is typically supplied by a different pulmonary artery. This can occur as a result of congenital or acquired abnormalities.

**Why the Correct Answer is Right:** In the normal anatomy, the pulmonary arteries are responsible for supplying blood to the lung parenchyma. The correct answer, **A. Segmental pulmonary artery**, refers to a smaller branch of the pulmonary artery that supplies blood to a specific segment of the lung. In a sequestered lung, due to its isolation, it may receive its blood supply from a different segmental pulmonary artery, which is why the correct answer is related to a segmental pulmonary artery.

**Why Each Wrong Option is Incorrect:**

A. **Branch of the aorta (ascending aorta)**: The aorta is the main trunk that carries oxygenated blood from the heart to the rest of the body. The branching pattern of the aorta does not match with the pulmonary circulation, making this option incorrect.

B. **Azygos vein**: The azygos vein is a systemic vein that drains blood from the upper half of the body into the superior vena cava. It is not involved in supplying blood to the lungs, making this option incorrect.

C. **Diaphragmatic branch of the intercostal artery**: This option refers to a branch of the intercostal artery, which supplies blood to the pleura and the intercostal muscles, not the lungs. This option is incorrect for a sequestered lung as it does not supply the required blood supply.

D. **Segmental pulmonary artery**: This answer is incorrect as it refers to a normal pulmonary artery that supplies blood to a specific lung segment. In a sequestered lung, it receives blood from a different segmental pulmonary artery, making this option incorrect.

**Clinical Pearl:** Understanding the anatomy of pulmonary circulation becomes crucial when assessing patients with sequestered lung. A sequestered lung may present with symptoms related to impaired oxygenation, ventilation, or infection due to the abnormal blood supply.

Correct Answer: **A. Branch of the segmental pulmonary artery**

In a sequestered lung, the abnormal sequestered lung receives its blood supply from a branch of the segmental pulmonary artery, instead of the typical segmental artery for that lung segment. This can occur due to congenital or acquired causes, leading to an abnormal blood supply and potentially causing symptoms such as dyspnea, hypoxia, or hemoptysis.