Smoker's Lungs vs. Normal Healthy Lungs

Visual, Cellular, Molecular, and Functional Changes in Smoker's Lungs

set of lungs with one side black with cigarette smoke beneath and the other side a healthy lung
What are the differences between smoker's lungs and healthy lungs?. Istockphoto.com/Stock Photo©monels

Many people remember hearing about the difference between smoker's lungs and normal healthy lungs in school. You may even recall the posters depicting the black, ugly-looking lungs of people who smoke. Does that really happen? What does cigarette smoke really do to the lungs?

Differences Between Smoker's Lungs and Normal Healthy Lungs

To really comprehend the effect of tobacco smoke on the lungs we need to take a look at both the anatomy—how the appearance of the lungs changes, and the physiology—how the function of a smoker's lungs differ from those of healthy lungs.

Yet we want to dig even deeper than that. What do a smoker's lungs look like beginning with the changes you can see with your naked eye, down to the genetic changes too small to even be seen under a microscope?

The posters we spoke of earlier didn't lie. Let's start with what you may see if you could look at whole lungs exposed to tobacco.

What Do Smoker's Lung Look Like?

The photo above is honestly what the lungs of a life-long smoker look like on a visual inspection with the naked eye. It's important to state that not all black lungs are related to tobacco smoke. Other irritants that can be inhaled may cause this appearance as well, such as the black lung disease sometimes seen in coal miners. Yet, it's very easy to tell when looking at a set of lungs whether or not a person smoked during his life.

Where does the black or brown color come from? When you inhale cigarette smoke, there are thousands of tiny carbon-based particles that are inhaled.

Our bodies have a special way of dealing with these particles to get them out of the way if you will.

As soon as you inhale a puff of cigarette smoke your body is alerted to the fact that toxic particles have invaded. Inflammatory cells rush to the scene. One type of white blood cell called macrophages may be thought of as the "garbage trucks" of our immune systems.Macrophages essentially "eat" the nasty brown-black particles in cigarette smoke in a process called phagocytosis.

Since these particles could be damaging even to garbage truck cells, they are walled off in tiny vesicles and stored as toxic waste. And there they sit. As more and more macrophages containing debris build up in the lungs and lymph nodes within the chest, the darker the lungs appear.

Smoker's Lungs at a Cellular Level

Taking a step down in size and looking at the lungs more closely, an increasing number of tobacco-related injuries are found. Under a microscope, the cells and surrounding tissues become visible as a well-appointed city, but a city ravaged by the toxic cloud of smoke that has descended upon it.

Cilia: The cilia are tiny hair-like appendages that line the bronchi,and the smaller bronchioles. The job of the cilia is to catch foreign material that finds its way into the airways and propel it up and out of the lungs to the throat in a wave-like manner. From the throat, this material can then be swallowed and destroyed by stomach acids.

Unfortunately, toxins in cigarette smoke such as acrolein and formaldehyde paralyze these tiny cilia so they cannot perform their function.

This results in other toxins (over 70 of them carcinogens) and infectious organisms being left within the lungs where they can do damage both at the cellular level and at the molecular level, changes that can, in turn, lead to cancer and other diseases.

Mucus: Inflammatory cells that are drawn to the scene in the airways secrete mucus in response to the harmful chemicals in cigarette smoke. This mucus can limit the amount of oxygen-rich air that reaches the smallest airways where gas exchange takes place. Mucus can also provide a nourishing breeding ground for the growth of harmful bacteria.

The Airways: Under the microscope, the airways can appear stretched out—like the elastic in an old pair of shorts. This decrease in elasticity caused by components of tobacco smoke has important functional repercussions as well (discussed later on.)

The Alveoli: The alveoli are the smallest of airways and the final lung based destination of oxygen that we breathe in. These alveoli contain elastin and collagen which allows them to expand with inspiration and deflate with expiration. Altogether, the surface area of your alveoli is around 70 square meters, and if you laid them flat and placed them end to end they would cover a tennis court.

Toxins in cigarette smoke damage these tiny structures in a few ways. It is easy for toxins to damage the thin walls causing them to rupture. Cigarette smoke also damages the alveoli that remain intact, decreasing their ability to expand and contract.

Damage to the alveoli is a self-perpetuating problem. As more alveoli become damaged, there is more air trapping in the alveoli (air cannot be breathed out) which results in the dilation and rupture of more alveoli. In general, a large percent of the alveoli must be damaged before symptoms—hypoxia  due to less oxygen being present for exchange to take place—occurs. Problems with oxygen exchange between the alveoli and capillaries are discussed further under function.

The Capillaries: At the cellular level, it's not just lung tissue that is damaged. The tiniest of blood vessels, the capillaries, that are closely associated with the smallest airways are also damaged by tobacco smoke. Just as smoking can cause the damage to larger blood vessels (which can eventually lead to heart attacks,) it can cause scarring and thickening of the capillary walls in the lungs—walls that oxygen needs to pass through in order to combine with the hemoglobin in red blood cells to be carried from the lungs to the rest of the body.

Smoker's Lungs at a Molecular Level: Genetics and Epigenetics

To really understand how smoking causes some lung diseases such as lung cancer, we need to look deeper inside the cells to the molecular level. This is a level that we can't see directly through a microscope.

In the nucleus of each of our lung cells lives our DNA—the blueprint of the cell. This DNA contains the instructions for making every protein that is needed for the cell to grow, function, repair itself, and tell the cell it is time to die when it becomes old or damaged.

You may have heard that a series of mutations in a cell is responsible for the link between lung cancer and smoking, but many mutations usually take prior to a cell becoming cancerous. In fact, there are usually thousands of mutations in a single lung cell exposed to tobacco.

Some genes in lung cells code for proteins that are responsible for the growth and division of the cell. One type of genes called oncogenes, cause cells to grow and divide (even when they shouldn't.). Other genes, called  tumor suppressor genes ,code for proteins which repair damaged DNA or eliminate damaged cells which cannot be repaired.

Several components in cigarette smoke have been found to cause mutations (they are carcinogenic) but studies have even shown ways in which tobacco specifically causes the damage which may lead to cancer. For example, some tobacco carcinogens cause mutations in the p53 gene, a tumor suppressor gene which codes for proteins which repair damaged cells or eliminate them so that a cancer cell isn't born.

Finally, in addition to genetic changes caused by smoking, tobacco can cause "epigenetic" changes in lung cells as well. Epigenetic changes refer not to actual changes in the DNA of a cell, but the way that genes are expressed.

Facts About the  Function of Smoker's Lungs vs Healthy Lungs: Physiology

Just as there are many changes that occur structurally in the lungs of someone who smokes, there are several changes which take place on a functional level as well.  Pulmonary function tests comparing those who smoke with those who do not smoke often show changes very early on, even in teens who smoke, and long before any symptoms occur.

Lung Capacity in Smoker's Lungs vs. Healthy Lungs

The total lung capacity, or the total amount of air you can breathe in taking the deepest breath possible is decreased by smoking in several ways. Smoking can result in damage to muscles in the chest reducing the expansion necessary to take a deep breath. The elasticity of the smooth muscle in the airways is likewise affected, and combined with the loss of elasticity, can limit the amount of air breathed in as well. And at a microscopic level, when fewer alveoli are present, or air can't reach the alveoli, the intake of breath is also affected. These forces all work together to decrease lung capacity.

In addition to lung capacity, smoking results in difficulty in exhaling the carbon dioxide that is transferred from the capillaries in the lungs to the alveoli. As noted above, decreased elasticity of the larger airways and decreased recoil of the alveoli leads to air trapping. This results in a decrease in  forced expiratory volume.

Thankfully, researchers have noted that one of the benefits of quitting smoking that occurs after only 2 weeks is an increase in both lung capacity and expiratory volume.

Oxygen Exchange in Smoker's Lungs vs. Healthy Lungs

It's not just the ability of oxygen to enter and pass down to the alveoli, or even the number of healthy alveoli present. Oxygen that reaches that alveoli must pass through the single cell lining of the alveoli and then through the double cell layer of the capillaries to reach the hemoglobin in red blood cells to be delivered to the rest of the body.

As noted above, cigarette smoke can affect both the alveoli and the lining of the capillaries making the passage of oxygen and carbon dioxide between the two more difficult. Not only is there less surface area available for gas exchange, but the exchange is compromised. It's harder for oxygen to pass through the scarred walls of the alveoli and capillaries. The diffusing capacity is a pulmonary function test which measures this ability of a gas to make this transition from the alveoli into the bloodstream.

Other Physiological Changes in the Lungs of a Smoker

There are many more changes that occur in the lungs of someone who smokes, and the ones mentioned here only touch the surface. While some of these changes are not reversible, it is never too late to quit smoking both to minimize the damage and to allow your body to repair the damage that can be restored and healed.

The Bottom Line: Lungs of a Smokers vs. Non-Smoker 

Looking at all of the structural and functional changes in the lungs of someone who smokes stresses the importance of smoking cessation, though it's not just the lungs that are of concern. There are a multitude of  diseases caused by smoking, with tobacco playing a role in nearly every body system. It is also not just lung cancer that is of concern. Take a look at this list of  cancers caused by smoking  if you still feel any reluctance to stop today.

Quitting Smoking: Help Is Available!

Thankfully, quitting smoking at any time can stop further damage from being done to your lungs and can reduce your risk of developing the diseases and cancers linked to the habit. We know it's not easy.Yet it's possible. Start today with quit smoking lesson 101 - reasons to quit in order to make this attempt your final and successful attempt to kick the habit.

Sources:

Baglietto, L., Ponzi, E., Haycock, P. et al. DNA Methylation Changes Measured in Pre-Diagnostic Peripheral Blood Samples are Associated With Smoking and Lung Cancer Risk. International Journal of Cancer. 2016 Sep 15. (Epub ahead of print).

Centers for Disease Control and Prevention. How Tobacco Smoke Causes Disease: The Biology and Behavioral Basis for Smoking-Attributable Disease: A Report of the Surgeon General. 2010. https://www.ncbi.nlm.nih.gov/books/NBK53021/

Gibbons, D., Byers, L., and J. Kurie. Smoking, p53 Mutation, and Lung Cancer. Molecular Cancer Research. 2014. 12(1):3-13.

Continue Reading