Humans consistently breathe out carbon dioxide (CO2). This continuous exchange of gases is a byproduct of energy production within the body’s cells. The respiratory system’s role involves taking in oxygen and expelling carbon dioxide.
How the Body Produces Carbon Dioxide
Carbon dioxide originates as a byproduct of cellular metabolism, specifically during cellular respiration. This process occurs continuously in nearly every cell, breaking down nutrients like glucose to generate adenosine triphosphate (ATP), the body’s primary energy currency. During cellular respiration, glucose and oxygen serve as inputs, while carbon dioxide, water, and energy (ATP) are the outputs.
Carbon dioxide production primarily takes place in the mitochondria during stages like the citric acid cycle (Krebs cycle) and pyruvate oxidation. As carbon atoms from broken-down nutrients are oxidized, they combine with oxygen to form carbon dioxide. This waste product then diffuses out of cells and into the bloodstream, establishing a concentration gradient that facilitates its movement.
How Carbon Dioxide is Expelled
Once produced in cells, carbon dioxide enters the bloodstream for transport to the lungs. It travels in the blood through three main methods: a small percentage dissolves directly in plasma, some binds to hemoglobin and other proteins, and the majority is transported as bicarbonate ions. This conversion occurs primarily within red blood cells, where carbon dioxide combines with water, a reaction accelerated by the enzyme carbonic anhydrase.
Upon reaching the lungs, this process reverses. Carbon dioxide diffuses from blood in the capillaries into the tiny air sacs called alveoli. The thin walls of the alveoli and surrounding capillaries allow for efficient gas exchange, where oxygen moves into the blood and carbon dioxide moves out. The respiratory system, including the diaphragm and other breathing muscles, then facilitates exhalation, expelling this carbon dioxide-rich air from the body.
The Importance of Exhaling Carbon Dioxide
Exhaling carbon dioxide is important for maintaining health. It serves as a metabolic waste product that must be removed to prevent harmful accumulation. If carbon dioxide levels build up in the blood, it leads to hypercapnia (or hypercarbia), which can cause symptoms like dizziness, fatigue, and shortness of breath. Persistent high levels can result in respiratory acidosis, where the blood becomes too acidic.
The body regulates carbon dioxide levels due to their direct influence on blood pH balance. Carbon dioxide combines with water in the blood to form carbonic acid, affecting the concentration of hydrogen ions. Maintaining the blood’s pH within a narrow range (typically 7.35-7.45) is necessary for proper cellular and organ function. If too much carbon dioxide is expelled, such as during hyperventilation, the blood can become too alkaline, known as respiratory alkalosis, leading to symptoms like dizziness and tingling. The respiratory system constantly adjusts breathing rate and depth to manage these levels and keep the body’s internal environment stable.