The Normal Lung

The Magnificent Lungs (Understanding the lungs and the role they play in your life)

A note by Dr Tom Petty, M.D.

Just about all of us are concerned about our health. Quite appropriately, the heart gets a lot of attention in this area; everyone knows that heart attacks are the number one cause of disability and death in this country. The heart is a remarkable pump that delivers blood to every organ in the body. When healthy, it does its job with a great amount of reserve. The popularity of jogging, walking, and other forms of exercise illustrates our new commitment to health through physical fitness.

It is amazing that only a few people have equal reverence for the lungs. After all, the lungs provide oxygen which is pumped by the heart and carried by the blood throughout our bodies—even to the heart itself!

Oxygen energizes every cell of the body. It is the key to the energy chain that keeps us living. A great amount of oxygen we take in is used to maintain cell and tissue structure.

Oxygen is required for all organ functions, including heart functions that are involved in every living activity. Oxygen is critical to the survival of all human beings. A shortage of oxygen affects every organ in the body. The brain has the highest oxygen requirement of all the organs. The heart has an immense oxygen requirement compared with the other organs in the body. The liver, kidneys, and all other organs require oxygen for their own vital functions. Thus, in states of oxygen deficiency, the whole body becomes robbed of vital energy.

Oxygen is involved in the process of metabolism, which converts food into the energy we need to live. The by-product of metabolism is carbon dioxide. The lungs remove carbon dioxide from the blood as it is returned from the tissues. When the lungs cannot exhale enough carbon dioxide, there is a toxic build-up, resulting in “acidosis,” an acid poisoning of all cells of the body. The brain, heart, and other organs are also impaired by carbon dioxide retention.

Understanding the lungs would be easy if they simply exchanged oxygen and carbon dioxide, but they do much more.

The lungs are the only organs in the body that receive the heart’s entire blood flow with each heartbeat. As blood from the veins flows to the right side of the heart and through the lungs, many of the body’s chemicals are either inactivated or activated by the lungs. For example, the lungs activate a hormone that controls blood pressure.

The lungs, through their normal function, affect our daily moods and emotions.

The lungs are the largest organ in the body. The total surface area is more than 100 square yards—the size of a tennis court. The delicate gas exchange membrane, or air-blood interface, is 1/50th the thickness of tissue paper. Millions of tiny capillaries carry red blood cells throughout the body, transporting oxygen in and carbon dioxide out. These red cells also contain mechanisms that defend against cigarette smoke, air pollution, and other noxious materials. Thus, the red cells are not only servants to every organ and tissue, but they are also the defenders against cancer, emphysema, and other lung diseases.

White cells, which defend us against infection, also traverse the lungs. In fact, at any one minute at least 17 billion white blood cells are cruising through our lungs. Billions are stored there, poised and ready to attack bacteria, viruses, and other infectious invaders that we inhale every day.

Nearly all of us know our height, weight, age, family background, and blood type. Virtually everyone has his or her blood pressure measured from time to time. Regular checkups of skin, breasts, and other organs can warn us well in advance of cancer. Yet rarely do we have a “lung checkup.” If the lungs are so critical to our health and happiness, why do we take them for granted?

Actually a “lung checkup” or vital capacity test is quite simple. The test measures the amount of air that can be blows out of fully inflated lungs. Vital capacity is a better predictor of longevity than other tests, including blood pressure, electrocardiograms, or blood tests. This breathing capacity has truly proven to be the capacity for life. But how many people know their own vital capacity? Testing devices are readily available, but unfortunately are used too infrequently in physicians’ offices. Indeed, two simple devices that cost less than $15 could be used by all Americans to test their vital capacity in their own homes.

The Effects of Smoking

You know that cigarettes are dangerous to those who smoke them. But even if you don’t use tobacco, you are not safe from the smoke emitted by someone else’s cigarette: passive smoke. Passive smoke contains more cancer-producing chemicals than the air in many chemical factories, uranium minutes, or asbestos factories. Cigarette smoke is more radioactive than many x-rays! A huge number of tobacco chemicals invade our body through the lungs unless we insist upon the right to breathe clean air. These chemicals can cause lung cancer, the most common fatal malignancy in both men and women. The carcinogens are also carried to other organs of the body, causing cancer of the bladder, uterus, and pancreas, etc. In fact, it is estimated that 30 to 50% of all cancer is caused by cigarette smoke.

Besides the risk of cancer, smoking doubles your risk of heart attack. And even if you don’t cancer or die from a heart attack, you are likely to develop chronic obstructive pulmonary disease (COPD), the fourth most common cause of death and second major cause of disability in our nation. Our society spends at least $2.5 billion a year for oxygen therapy and many more billions for respirators in intensive care units.

Tobacco kills approximately 1,500 Americans each day. But we continue to allow tobacco sellers to advertise their deadly products. It is estimated that 4,000 people have died in Bhopal, India since the world’s greatest industrial disaster in 1984, but we accept 450,000 deaths per year as a matter of personal preference. Court dockets are full of claims against the asbestos, minimal, and chemical industries. However, our billboards, magazines, and newspapers continue to sell heart attack, cancer, and COPD. Why do we continue to promote suffering and death?

What is the answer to this paradox?

1. The first step is to recognize the lungs as major health organs. We must identify lung health as the basis for a healthy, happy, long life.

2. We must learn about the condition of our own lungs and be able to protect them.

3. We must support legislation against smoking in public places and against tobacco advertising of all types, including the endorsement and sponsorship of sporting events.

4. Finally, we must continue in our research efforts to understand the basic mechanisms of lung injury through smoking. In the interim, before smoking is dramatically reduced in this country, we will continue to develop and evaluate new methods of care for COPD sufferers, as we have during the past 35 years.

Anatomy of the Lungs

The lungs should be considered “the environmental organ.” They are unique in their size and formation, and they interface with all the materials you inhale from the community environment, the work environment, and the personal environment. The lungs are made up of a series of branching tubes that provide the pathways for air entry and exit. These pathways, called bronchi, are exquisite in their design, with each tube branching twice: The major airway or windpipe (trachea) divides into two main bronchi, which in turn beget smaller and smaller orders of bronchi until some 22 divisions result in the final conducting passageways.

The respiratory or gas exchange function of the lungs begins in tiny sacs or folded structures (alveoli) attached to these tiny passageways. These smallest passageways continue to branch and finally connect with alveolar ducts, passageways thoroughly lined by alveoli. Each duct ends in a mass of alveoli. The avelolar-capillary membrane lines all of the alveoli and works as the blood-air interface. It allows life-giving oxygen into the blood and extracts the waste gas, carbon dioxide, from the blood. As stated earlier, this delicate membrane is only 1/50^th the thickness of tissue paper, thin enough to transport oxygen and carbon dioxide, but still a barrier against fluid formation within the alveolar spaces.

The total surface of the alveolar membrane varies from 100 to 200 square meters, depending on the size of the person. The overall surface area of the alveolar membrane has frequently been equated to that of a tennis court. This comparison is really an underestimation! Thus, the lungs are by far the largest organs that make intimate contact with the environment.

The lungs are also the only organs of the body that receive all the blood from the heart with every heartbeat. Thus, any material in the bloodstream circulates through the lungs constantly. Some materials, such as small blood clots, can injure the membrane and cause the lung to leak fluid. Infections can cause pneumonia, and heart failure can flood the lungs. In these conditions, gas exchange becomes abnormal.

People who truly understand the lungs marvel at their complexity. Consider that roughly 100,000 small air passages that feed a membrane surface area greater than the size of a tennis court! This membrane wraps itself around at least 300 million alveoli and is lined with a myriad of tiny blood vessels called capillaries. Consider further the fact that approximately four quarts of air pass through the gas-exchange surface each minute, along with some five liters of blood, which traverse the capillary membrane. This magnificent machine occupies the chest cavity and, in all, is some 4 to 6 quarts of total volume. We certainly must consider the lungs the most exquisite packaging job in nature, and their function a splendid orchestration. Only the brain possesses greater complexity and capability in design and function.

Naturally, the lungs must be defended against outside damage, and recent research revealed some fascinating defense mechanisms. The nose acts as a filter, and the conducting air passages contain a protective mucous lining. Within the lungs, tiny hair-like cells called cilia sweep the air entering the lungs almost constantly, acting as janitors. Scavenging cells, called macrophages, are poised and ready to engulf particles that evade their sentinels. Macrophages are potent obstacles to damage from the environment, but these cells can release enzymes that damage the lung’s delicate structure.

Small amounts of normal lung fluids also help the lungs defend themselves. The surfactant system of the lungs allows easy filling and emptying of the lungs. Surfactant also provides an antibacterial and immune function to protect against infections.

Within the blood vessels of the lungs, an anti-clotting system combats small accumulations of damaging cells, aggregates, and small clots that enter the lungs from other parts of the body.

Thus, normal lung fluids are being formed and washed away constantly. The lungs have anti-irritants, anti-infectives, anti-enzymes, and immune defense mechanisms, all of which are coordinated to serve these organs well.

The gas-transfer function of the lungs is well understood today. (In fact, everyone should learn about this process, the essence of normal organ system function. Information on the topic is available in schools and in the numerous health-oriented articles that appear in the print media today). The biochemical or non-respiratory functions of the lungs are less recognized. We continue to marvel at the hormonal activities of the lungs that, as mentioned earlier in this chapter, regulate other functions of the body, possibly including the brain. Thus, the lungs work in cooperation with the brain, and are the main control system for the body. The lungs are unequaled in their diversity of functions and contributions to the health of the individual.

Thus, the chest, containing both lungs and heart, is not a “block box.” Let’s reconsider the orchestration of the lungs mentioned earlier in this chapter. This symphony includes 300 million alveoli and at least 100,000 small airways, as well as the larger airways, working together with each breath that leaves our body, some 12 to 20 times a minute. We consider the lungs to be the “pulmonary philharmonic” of our body. The heart, which pumps the blood, is the “cardiac choreographer.” For as words flow from a pen and move across the page, so the blood from the lungs is moved by the heart to serve all the organs of the body. But the “pulmonary philharmonic” and the “cardiac choreographer” must have a conductor. The “conductor” is the brain, our most vital control system. The whole human brain, including consciousness and awareness, is the conductor. And, as respiration and circulation are the “recital,” metabolism which fuels all bodily functions is the “melody.” Only the individual can perceive and know his or her own melody, the pitch, the tone, and the meter. In illness, we can all feel the decrescendo of despair. Can we once again ascend with a new cadenza and revel in rhapsody? Good music lasts and lingers on!

This brief essay and the suggested reading that follows are intended to stimulate further study, contemplation, and philosophizing about the lungs as the unique organs they are and about the various roles they play in the health and happiness of the whole human being.

Suggested Reading Scientific:

1. Murray, JF: The Normal Lung (The Basis for Diagnosis and Treatment of Pulmonary Disease). 2^nd Edition, Philadelphia, W.B. Saunders, 1986.