The Lungs
The lungs are the organ system most effected by the environment. We have to breathe to survive and unlike food, air is free, ubiquitous, omnipresent and necessary no matter where we go. Unfortunately, we can very rarely control the quality of the air we breathe and can only control the quantity (how many breaths we take). If that air has any noxious gas, odor, toxin or chemical in it, our bodies can only filter out so much. Lung exposures such as smoke, ozone, car exhausts, particulate matter from burning fossil fuels or other combustibles and chemicals can cause children or adults with respiratory conditions to have trouble breathing. People with asthma or allergies are often prone to exacerbations when exposed. Tobacco smokers or e-cigarette users take in thousands of chemicals, poisons and air pollutants with each puff they take. Think about this the next time you walk down the street and an inconsiderate smoker blows cigarette smoke in your direction.
Representative cartoon of the lungs with a magnified cartoon of an alveolus with an adjacent capillary (the so-called gas exchange unit of the lungs). Click to enlarge. Cartoons are drawn by the BreathingNYC team.
Anatomy of the Lungs
The lungs can be divided into three basic components: 1) the upper airway (nose, oropharynx or throat and larynx or voice box), 2) the lower airways (trachea, bronchi, bronchioles, alveoli) and 3) the blood vessels of the lungs. Each component serves a specific function all with the main goals of bringing in oxygen (necessary for our body to make energy) and getting rid of carbon dioxide (a waste product created as we use energy stores).
Representative cartoon of the upper airway which includes the nose, the oropharynx (tongue and throat) and the larynx (vocal cords). Click to enlarge. Cartoons are drawn by the BreathingNYC team.
Upper Airway
The upper airway consists of the nose, the oropharynx and the larynx. The nose helps to heat and humidify air as it enters the body. Within the upper airway one has the tonsils and the adenoids which act as immune organs “filtering” out harmful bacteria. The epiglottis covers the vocal cords during the act of swallowing, protecting the vocal cords and allowing food to enter the esophagus. The vocal cords (or larynx) both serve as a way to help us communicate through phonation (speech) but also help to protect our lungs from fluid or food entering the lower airways. Click HERE to learn more about the upper airway.
The airways branch from the trachea to the alveoli more than 23 times. As the branch more and more, the conducting (no gas exchange) airways become smaller and smaller progressing from trachea to mainstem bronchi, through the segmental bronchi, bronchioles and to the terminal bronchioles. Beyond the terminal bronchioles, the respiratory airways (can exchange gas) begin with the respiratory bronchioles, extend to the alveolar ducts and then to the alveolar sacs. Cartoons are drawn by the BreathingNYC team.
At the terminal airways or terminal bronchioles, gas exchange can begin to occur. Oxygen enters the alveoli, pulmonary arteries (blue) bring deoxygenated blood to the alveoli where they release carbon dioxide and pick up available oxygen as they transition through capillaries (purple) and then enter pulmonary veins (blue). The bronchial arteries carry oxygenated blood to the large airways and supply them with nutrients. Lymphatics help to reduce the amount of liquid outside of the blood vessels and carry lots of immune related proteins and cells. Cartoons are drawn by the BreathingNYC team.
Lower Airway
The lower airways consist of the large conducting airways (trachea and bronchi) that connect the upper airway to the areas of gas exchange (the alveoli). The smallest airways are called bronchioles and are the location where bronchiolitis and asthma occur. Once the gas passes through the lower airway, it enters the alveoli where it diffuses across a very thin membrane into the blood vessels (capillaries) adjacent to the alveoli. Oxygen can then be transported via red blood cells and transported throughout our body via the blood vessels.
Representative cartoon pulmonary blood vessels. Venous (deoxygenated blue blood) enters the heart where it is pumped to the pulmonary arteries (blue) to the alveoli (gas exchange units) and is oxygenated. Oxygenated blood (red blood) returns to the heart through the pulmonary veins (red) and is then pumped to the body through the aorta (bright red). Click to enlarge. Cartoons are drawn by the BreathingNYC team.
The Blood Vessels of the Lungs
The heart and the lungs are closely related. Deoxygenated blood returns from the body to the right side of the heart. The right side of the heart then pumps this blood to the lungs where it receives oxygen at the gas exchange units (alveolar-capillary nits). The oxygenated blood then returns to the left side of the heart where it is then pumped out to the body to use as energy. Importantly, as oxygen is utilized by the body’s tissues, carbon dioxide, a waste product of energy expenditure (metabolism) is picked up by the blood and brought back to the heart. In the gas exchange units of the lung, carbon dioxide leaves the blood into the alveoli where it is then exhaled into the environment.
Another representative cartoon summarizing the process of gas exchange with deoxygenated blood (blue) returning to the right side of the heart passing through the pulmonary artery and subsequently through the alveolar-capillary bed where red blood cells bind with oxygen and eliminate carbon dioxide, finally returning oxygenated blood (red) through the pulmonary veins, back to the left side of the heart and on to the systemic circulation. Cartoons are drawn by the Breathing NYC Team.
Breathing
The act of breathing is relatively straight forward. The large muscle at the bottom of the rib cage (the diaphragm) contracts and brings air into the chest, inflating the lungs. This is an active process and requires energy. Under normal conditions, we don’t use energy when we exhale. The diaphragm relaxes and we passively exhale.
The regulation of this process is not so straight forward. There is a complex interaction between the brain, the brainstem (the part that connects the brain to the spinal cord), the nerves that connect the brainstem to the muscles of respiration and finally, the muscles of respiration. We can control our breathing through conscious thought, but most of our breathing occurs subconsciously, meaning we don’t have to think about it. There are neurologic and chemical signals that help to maintain the frequency and depth of our breaths without us even thinking about it. Three of the most important chemicals include oxygen, carbon dioxide and the acidity level (pH) of our blood.
As we take a deep breath in, we bring oxygen into our blood stream and eliminate carbon dioxide. Carbon dioxide is a byproduct of our body creating and using energy. When we exercise, we create more carbon dioxide and therefore breathe faster to eliminate it. A high carbon dioxide level in our blood can make our blood quite acidic and can be a problem under certain circumstances.
Abnormalities in this process can lead to significant problems and can contribute to chronic respiratory failure. It’s easy to check an oxygen level through a pulse oximeter at your pediatrician’s office, however it’s not so easy to check a carbon dioxide level. This may require a blood draw unfortunately, but may be necessary under certain circumstances.