What Are Lobes In The Lungs

Lobes are the large, distinct sections of each lung, separated by deep grooves called fissures. Your right lung has three lobes and your left lung has two, giving you five in total. This asymmetry exists because the heart sits slightly left of center in the chest, leaving less room on that side. What makes lobes interesting beyond the basic anatomy is how much the real picture varies from the textbook diagram, how they move independently during breathing, and why surgeons care so much about the fissures between them.

How the Five Lobes Are Arranged

The right lung is divided into three sections: an upper lobe, a middle lobe, and a lower lobe. Two fissures create these divisions. A long diagonal groove called the oblique fissure separates the lower lobe from the upper and middle lobes. A shorter, roughly horizontal groove called the horizontal fissure separates the upper lobe from the middle lobe.

The left lung has only two lobes: upper and lower, separated by a single oblique fissure. Instead of a middle lobe, the left lung has a small tongue-shaped projection called the lingula, which hangs off the front edge of the upper lobe. The lingula occupies roughly the same space that the middle lobe occupies on the right side, and it can develop similar problems, but anatomically it is part of the upper lobe rather than a separate lobe of its own.

Each lobe is further divided into segments, each with its own airway and blood supply. The right lung has ten segments and the left has eight to ten, depending on how the anatomy is classified. Segments matter for targeted treatments and smaller surgical procedures, but the lobe remains the primary functional and surgical unit that most people encounter in medical discussions.

Fissures Are Rarely Textbook-Perfect

Anatomy textbooks draw fissures as clean, complete lines separating the lobes like slices in an orange. In living people, the picture is much messier. A large systematic review and meta-analysis of studies on lung fissure anatomy found that the right horizontal fissure was complete in only about 54% of people, incomplete in 35%, and entirely absent in 11%. The right oblique fissure was complete in roughly 77% of cases, and the left oblique fissure in about 72%.¹ A separate large surgical series found even higher rates of incompleteness during actual operations, with the major fissure incomplete in over 80% of right lungs and over 66% of left lungs examined in the operating room.²

An incomplete fissure means the lung tissue between two lobes is partially fused rather than fully separated. In some spots the lobes are barely distinguishable from one another. This is not a disease or a defect. Researchers now describe incomplete fissures as “the predominant anatomical norm rather than an anomaly.”² The “complete fissure” of the textbook is actually the less common version.

Why does this matter? When a fissure is incomplete, infection or fluid in one lobe can spread more easily into an adjacent lobe, since there is no clear tissue boundary stopping it. On imaging, an incomplete fissure can also make it harder to tell which lobe a shadow or mass belongs to. Automated software tools that try to segment CT scans into individual lobes struggle with this, since roughly 80% of patients have fissures that are incomplete or hard to distinguish from nearby blood vessels and airway walls.³

Lobes Slide Against Each Other When You Breathe

During each breath, the lobes of your lungs do not expand as a single rigid block. They actually slide relative to one another along the fissure surfaces, somewhat like tectonic plates shifting on a much smaller and faster scale. This sliding motion is made possible by a thin layer of lubricating fluid between the fissure surfaces.⁴

This lobar sliding serves an important purpose. Research using computational lung models has shown that when lobes are allowed to slide freely, the lung tissue experiences less internal distortion during breathing compared to models where the lobes are stuck together. The effect is most pronounced in the lower lobes, where the reduction in tissue strain was statistically significant.⁵ In other words, having separate lobes that can move independently helps the lung inflate more evenly and with less mechanical stress on the tissue. When disease or scarring causes fissure surfaces to stick together, known as pleural adhesion, this sliding is reduced, and the lung may not expand as smoothly.

Engineering models of this sliding behavior confirm that the discontinuity in tissue movement at the fissure boundary is a real, measurable feature of lung mechanics, not just a theoretical prediction.⁶ Understanding how lobes move relative to each other has practical applications in radiation therapy planning and in building better computer models of lung deformation during breathing.

Upper Lobes and Lower Lobes Are Not Interchangeable

Gravity has a surprisingly large effect on how the lungs work when you are upright. Both blood flow and ventilation are greater in the lower lobes than in the upper lobes. This means the lower lobes do more of the gas exchange work during normal breathing. The regional differences go beyond just air and blood: lymphatic flow, metabolism, and the mechanical properties of the tissue all vary from top to bottom.⁷

This regional non-uniformity helps explain why certain lung diseases prefer certain locations. Tuberculosis, for example, classically sets up in the upper lobes, which seems counterintuitive given that the lower lobes get more blood flow and ventilation. The relative under-perfusion and different mechanical environment of the upper lobes may create conditions more favorable to certain infections. Emphysema, too, often shows an upper-lobe-predominant pattern, while other conditions like pulmonary fibrosis tend to start in the lower lobes. Knowing which lobe is affected tells a clinician something about what the disease might be, not just where it is.

Lymph Drainage Follows Lobe-Specific Pathways

Each lobe has its own network of lymphatic channels, and these networks do not all drain to the same place. Research on lymphatic anatomy has mapped how the drainage routes differ by lobe in the right lung. The upper lobe segments frequently drained directly to lymph nodes near the trachea, with more than half of the segments studied sending their lymph straight to those nodes, bypassing the closer intrapulmonary and hilar nodes entirely. The middle lobe drained predominantly to a different set of nodes between the bronchi. The lower lobe had the most variable drainage, with some segments sending lymph to nodes belonging to other lobes, and some draining downward toward the abdomen.⁸

This lobe-specific drainage has real consequences for cancer surgery. Lung cancer spreads to the mediastinum through these lymphatic channels, and the drainage does not always follow a predictable lobe-to-node route. In studies correlating anatomy with surgical findings, lymphatic drainage sometimes reached mediastinal nodes that did not correspond to the anatomical location of the tumor.⁹ This is why surgeons performing cancer operations sample lymph nodes from multiple stations rather than just the ones closest to the tumor. The lobe the cancer sits in gives a starting point for where to look, but the lymphatics can take unexpected detours.

Surgical Removal of a Lobe

Lobectomy, the surgical removal of an entire lobe, is one of the most common operations for early-stage lung cancer. The lobar structure of the lung makes this practical: a surgeon can remove one discrete section while leaving the rest functioning. For smaller, early-stage tumors, surgeons sometimes perform a segmentectomy instead, removing just one or two segments rather than the whole lobe. Research comparing these two approaches for early non-small cell lung cancer found that outcomes were similar when the tumor had not spread through air spaces. But when tumors showed a specific pattern of microscopic spread, removing the entire lobe produced better survival than removing only a segment.¹⁰

The completeness of the fissures matters here too. When a surgeon needs to separate a lobe from its neighbor during a lobectomy, a complete fissure makes the dissection straightforward. An incomplete fissure means the surgeon has to cut through fused tissue, which increases the risk of air leaks and bleeding. Surgeons increasingly use preoperative CT scans to assess fissure completeness and plan their approach accordingly. Techniques like “fissureless lobectomy” have been developed specifically to handle incomplete fissures safely.²

How the Remaining Lung Compensates

After a lobe is removed, the remaining lung tissue does not simply sit there unchanged. The residual lobes expand to fill the empty space, and their function increases proportionally. A study comparing recovery after upper versus lower lobectomy found that the remaining lung expanded to varying degrees, with functional gain tracking the amount of anatomic expansion. Interestingly, this compensatory expansion was more pronounced after lower lobectomy than after upper lobectomy, yet the net loss of lung function ended up about the same regardless of which lobe was removed, around 10-14%.¹¹

The compensatory process involves more than just stretching. In animal studies where multiple lobes were removed, the remaining lung grew new blood vessels to handle the increased blood flow. When two of the right lung’s lobes were removed in rats, the left lung’s arterial area increased by about 26%, and the ratio of small blood vessels to air sacs stayed normal. But when three right lobes were removed, the vascular growth could not fully keep up: small vessel density dropped by about 30% relative to air sacs, the walls of small arteries thickened, and the right side of the heart enlarged from the extra workload.¹² The lung has a real capacity for compensatory growth, but that capacity has limits. Losing too much tissue can push the remaining vasculature into a state of strain.

The Azygos Lobe and Other Anatomical Extras

Some people have an extra partial lobe that does not appear in the standard anatomy. The best known of these is the azygos lobe, a small accessory lobe in the upper part of the right lung created when the azygos vein takes an unusual path through the lung during embryonic development. A meta-analysis of over a million subjects estimated the overall prevalence of the azygos lobe at about 0.3%, though individual studies have reported rates as high as 1.2%.¹³ The azygos lobe was found roughly twice as often in men as in women, and its prevalence was about 17 times higher in people who also had other congenital lung defects, suggesting a possible genetic component.¹³

The azygos lobe almost never causes symptoms on its own. Most people who have one never know it. It shows up as an incidental finding on a chest X-ray or CT scan, identifiable by a characteristic thin curved line called the azygos fissure sweeping across the upper right lung. The main clinical relevance is that radiologists and surgeons need to recognize it so they do not mistake it for something abnormal or run into surprises during procedures in that area.¹⁴

Beyond the azygos lobe, accessory fissures can create additional pseudo-lobes elsewhere in the lung. The meta-analysis of fissure variations found accessory fissures in about 14% of lungs on both sides. The most common accessory fissure on the right was the inferior accessory fissure (about 6%), and on the left it was the left minor fissure (about 8%).¹ These extra fissures do not create truly independent lobes with their own blood supply and airways, but they can create visual confusion on imaging and change how infections or fluid collections are contained within the lung.

How Lobes Form Before Birth

The lobes take shape early in embryonic development as the lung buds branch and the fissures form between them. Research in animal models has identified specific proteins required for the lobes to separate properly. One protein called nephronectin appears to be necessary for maintaining the boundaries between lobes on the right side. In mice engineered to lack this protein, the right lung lobes formed initially but then fused together, primarily the middle and lower lobes, starting around midway through gestation and persisting into adulthood.¹⁵

In humans, a range of congenital lung anomalies can affect lobar anatomy. Some involve extra lobes, absent lobes, or abnormal connections between the lung tissue and the blood supply. Many of these are detected incidentally, without ever causing symptoms. Others, particularly in newborns, can be life-threatening if not identified and treated quickly. The difficulty in classifying congenital lung anomalies is that they can involve the airways, the arteries, the veins, the lung tissue itself, or combinations of all of these, since the lung develops from multiple embryonic structures simultaneously.

Endobronchial Valves and Lobe-Targeted Treatment for Emphysema

One of the more striking applications of lobar anatomy in modern medicine involves treating severe emphysema without surgery. In emphysema, damaged portions of the lung become hyperinflated and trap air, squeezing the healthier tissue around them and making it harder for the diaphragm to work efficiently. Lung volume reduction surgery, which removes the most damaged sections, has been shown to help selected patients, but it is a major operation.

A less invasive alternative uses tiny one-way valves placed through a bronchoscope into the airways feeding the most damaged lobe. These endobronchial valves block air from entering the targeted lobe while allowing trapped air and secretions to escape. Over time, the treated lobe deflates, giving the healthier remaining lobes more room to expand. This approach is now a guideline-recommended treatment for advanced emphysema.¹⁶

The effectiveness of endobronchial valves depends heavily on fissure completeness. If the fissure between the treated lobe and the adjacent lobe is incomplete, air can sneak around the valves through the fused tissue, and the targeted lobe will not deflate properly. This is why preoperative imaging to assess fissure integrity is a critical step before valve placement. A randomized trial found that the valves produced modest improvements in lung function, exercise capacity, and symptoms, but also came with higher rates of pneumonia and flare-ups of lung disease after placement.¹⁷ Patient selection, particularly identifying people with complete fissures and the right pattern of disease distribution among the lobes, has been the focus of refining this technique.

The endobronchial valve story illustrates a broader principle about lung lobes: the divisions between them are not just anatomical landmarks. They are functional boundaries that clinicians exploit for diagnosis, surgery, and targeted therapy. The better you understand where one lobe ends and the next begins, and whether that boundary is complete or porous, the better you can direct treatment to the part of the lung that needs it while leaving the rest alone.

1
PubMed. Anatomical Variations of the Lung Lobes and Fissures: A Systematic Review and Meta-Analysis
2
PubMed. Intraoperative assessment of pulmonary fissure morphology in a large surgical series: implications for operative strategy
3
PubMed Central. Fully Automated Lung Lobe Segmentation in Volumetric Chest CT with 3D U-Net: Validation with Intra- and Extra-Datasets
4
PubMed Central. A measure for characterizing sliding on lung boundaries
5
PubMed Central. Role of lung lobar sliding on parenchymal distortion during breathing
6
Applications in Engineering Science. Contact mechanics model of lung lobar sliding
7
PubMed. Upper lobe lung disease: physiologic correlates
8
PubMed. Anatomical variations in lymphatic drainage of the right lung: applications in lung cancer surgery
9
PubMed. Anatomic basis of lymphatic spread of lung carcinoma to the mediastinum: anatomo-clinical correlations
10
PubMed. Tumour spread through air spaces is a determiner for treatment of clinical stage I non-small cell lung Cancer: Thoracoscopic segmentectomy vs lobectomy
11
PubMed. Compensation of pulmonary function after upper lobectomy versus lower lobectomy
12
PubMed. Vascular growth and remodeling in compensatory lung growth following right lobectomy
13
PubMed. The prevalence of the azygos lobe: A meta-analysis of 1,033,083 subjects
14
PubMed Central. Azygos Lobe: Prevalence of an Anatomical Variant and Its Recognition among Postgraduate Physicians
15
PubMed Central. Nephronectin is required to maintain right lung lobar separation during embryonic development
16
PubMed Central. Endobronchial Valves for the Treatment of Advanced Emphysema
17
PubMed. A Randomized Study of Endobronchial Valves for Advanced Emphysema