Your lungs are divided into five separate sections called lobes: three on the right side and two on the left. These lobes function as semi-independent units, each with its own airway, blood supply, and surrounding membrane. This design allows one lobe to be diseased or even surgically removed without necessarily destroying the function of the others.
How the Five Lobes Are Arranged
The right lung has three lobes: the right upper lobe, the right middle lobe, and the right lower lobe. The left lung has only two: the left upper lobe and the left lower lobe. The left side is smaller because the heart sits slightly to the left of center in your chest, taking up space that would otherwise be lung tissue. Overall, the right lung accounts for about 54% of your total lung volume, while the left lung makes up the remaining 46%.
On the left lung, a small tongue-shaped projection called the lingula extends from the upper lobe. It sits right along the indentation where the heart nestles against the lung. The lingula is essentially the left lung’s version of the right middle lobe, occupying a similar position and serving a similar function, even though it isn’t separated into its own distinct lobe.
What Separates One Lobe From Another
The lobes are divided by thin folds of tissue called fissures. These are double layers of the membrane that lines the lungs, and they extend deep into the lung tissue to create real physical boundaries between lobes.
The right lung has two fissures. An oblique fissure runs diagonally from back to front, separating the lower lobe from the upper and middle lobes. A horizontal fissure then runs roughly level across the front of the lung, dividing the upper lobe from the middle lobe. The left lung has just one oblique fissure, which separates its upper lobe from its lower lobe.
Some people have extra fissures that don’t appear in textbook anatomy. These accessory fissures can subdivide a lobe further. For example, a superior accessory fissure may split the top portion of a lower lobe from the rest, or an azygos fissure can section off a small piece of the right upper lobe where a vein drapes through the tissue. These variations are common enough that doctors look for them on imaging scans before planning any procedure.
Segments Inside Each Lobe
Each lobe is further divided into smaller units called bronchopulmonary segments. Think of lobes as the major chapters of the lung, and segments as the sections within each chapter. Each segment has its own branch of airway and its own artery, making it a self-contained functional unit.
The right upper lobe contains three segments, the right middle lobe has two, and the right lower lobe has five. On the left side, the upper lobe (including the lingula) contains four segments, and the left lower lobe has four. That adds up to roughly 18 to 19 segments across both lungs, depending on small variations between individuals. These segments matter in surgery because a surgeon can sometimes remove just one segment rather than an entire lobe, preserving more healthy tissue.
Why the Lungs Are Divided This Way
The lobar structure isn’t just anatomical trivia. Because each lobe is physically separated by fissures and has its own airway and blood supply, the lobes are partially isolated from one another. This isolation helps contain certain diseases within a single lobe rather than letting them spread freely across the entire lung. An infection, tumor, or area of damage in one lobe doesn’t automatically compromise the others.
This containment is what makes a lobectomy (surgical removal of one lobe) a viable treatment. A surgeon can remove a diseased lobe while the remaining lobes continue to function. Over time, the remaining lung tissue can expand somewhat to fill the empty space. For early-stage lung cancer, removing the affected lobe is the standard surgical approach and offers strong long-term survival rates, provided the patient has enough overall lung capacity to tolerate the loss.
How Lobes Appear on Imaging
On a CT scan, the fissures between lobes show up as thin bright lines or as narrow bands where no blood vessels or airways cross. Radiologists use these fissure lines, along with the branching pattern of airways and blood vessels radiating outward from the center of the chest, to identify exactly which lobe a problem is located in. Vessels and airways appear as tubes, ovals, or circles depending on the angle the scan catches them, and their positions are predictable enough that doctors can pinpoint individual segments within each lobe.
On a standard chest X-ray, the fissures are harder to see, but lobar pneumonia often makes the boundaries obvious. When infection fills one lobe with fluid, that lobe appears as a dense white region with borders that follow the fissure lines. This is one way doctors distinguish lobar pneumonia, which fills an entire lobe, from bronchopneumonia, which creates scattered patches throughout both lungs without respecting lobar boundaries.
Conditions That Affect Individual Lobes
Several lung diseases tend to favor specific lobes. Tuberculosis, for instance, most commonly affects the upper lobes. Aspiration pneumonia, caused by accidentally inhaling food or liquid, tends to settle in the right lower lobe because the right main airway is wider and more vertical, making it the path of least resistance for inhaled material.
Lung cancer can develop in any lobe, but the location influences symptoms and treatment options. A tumor in an upper lobe may cause shoulder or arm pain, while one in a lower lobe might go unnoticed longer because it’s farther from the major airways. When cancer is confined to a single lobe without spreading to lymph nodes or other organs, removing that lobe alone is often enough. For patients whose lung function is too compromised to tolerate losing a full lobe, surgeons may remove just the affected segment or use radiation instead.
Emphysema, a component of chronic obstructive pulmonary disease, can also be lobe-specific. When damage is concentrated in the upper lobes, a procedure called lung volume reduction surgery removes the most destroyed tissue, allowing healthier lower lobes to expand and work more efficiently.