How many lobes does the right lung have and how many on the left?

• A. Right lung has three lobes; left lung has two lobes.
• B. Right lung has two lobes; left lung has three.
• C. Left lung has four lobes.
• D. Both lungs have three lobes.

Answer: (A)

Lobar structure is defined by the fissures that divide the lungs. The right lung has two fissures—the horizontal and the oblique—so it is divided into three lobes: upper, middle, and lower. The left lung has only the oblique fissure, which creates two lobes: upper and lower. The left side is smaller and has a cardiac notch, a reflection of the heart’s position, which helps explain why there isn’t a third lobe on that side. So the right lung has three lobes and the left lung has two.

The other options don’t fit because there isn’t a third lobe on the left, there isn’t a fourth lobe on the left, and having both lungs with three lobes would ignore the left lung’s lack of a horizontal fissure that would create a middle lobe.