When we breathe, we inhale a mixture of gases, including a small amount of carbon dioxide. This inhaled carbon dioxide is not harmful and is a normal part of the atmosphere. Understanding the air we breathe and how our bodies manage gases is key to respiratory health.
The Air We Inhale
The air surrounding us is a blend of gases, primarily nitrogen (approximately 78.08%) and oxygen (about 20.95%). Carbon dioxide is present in a much smaller concentration, around 0.04% to 0.042% by volume. This inhaled carbon dioxide is not harmful. Atmospheric carbon dioxide originates from natural processes like volcanic activity, the decomposition of organic matter, and the respiration of living organisms. Human activities, particularly burning fossil fuels and deforestation, have significantly increased these levels, reaching about 50% higher than pre-industrial levels.
The Body’s Carbon Dioxide Production
While we inhale a small amount of carbon dioxide, most of the carbon dioxide in our body is produced internally as a natural waste product of metabolic processes. Every cell produces energy through cellular respiration. During this process, cells use oxygen and nutrients, primarily glucose, to produce adenosine triphosphate (ATP). These reactions break down glucose, yielding energy, water, and carbon dioxide as byproducts. The carbon dioxide then diffuses into the bloodstream and is carried to the lungs for removal.
Maintaining the Right Balance
The body possesses sophisticated mechanisms to regulate carbon dioxide levels, ensuring a stable internal environment, with the lungs playing a central role by efficiently removing the internally produced carbon dioxide from the bloodstream through exhalation. This gas exchange occurs in the alveoli, tiny air sacs in the lungs, where carbon dioxide moves from the blood into the air to be breathed out. The brain, specifically the medulla oblongata in the brainstem, closely monitors carbon dioxide levels in the blood and cerebrospinal fluid; specialized sensory cells called chemoreceptors, located in the medulla and in major arteries like the aorta and carotid arteries, detect changes in blood carbon dioxide and pH. When carbon dioxide levels rise, these chemoreceptors signal the brain to increase the rate and depth of breathing, effectively expelling more carbon dioxide and restoring balance. An imbalance, such as too much carbon dioxide accumulating in the body, known as hypercapnia, can lead to symptoms like headaches, dizziness, fatigue, and can cause respiratory acidosis, impacting overall health.