On average, humans take about 15 breaths per minute, and their lungs move about 0.5 liters of air in a quiet breathing cycle. Describe the cycle of breathing.
The cycle of breathing involves a series of movements and processes that allows air to flow in and out of our lungs. It can be divided into two main phases: inhalation and exhalation.
During inhalation, the diaphragm and intercostal muscles contract. The diaphragm, a dome-shaped muscle beneath the lungs, moves downward, while the intercostal muscles between the ribs expand the chest cavity. This expansion creates a negative pressure in the chest, causing air to rush into the lungs through the nose and/or mouth. The air travels down the trachea, through the bronchial tubes, and into the lungs. It eventually reaches the alveoli, which are tiny air sacs where oxygen is exchanged with carbon dioxide.
Once the lungs are filled with fresh oxygen, exhalation begins. The diaphragm and intercostal muscles relax, causing the chest cavity to decrease in size. This contraction increases the pressure in the lungs, forcing stale air, rich in carbon dioxide, out of the lungs and back through the respiratory system. From there, it is expelled from the body through the nose and/or mouth.
This process of inhalation and exhalation repeats continuously throughout the day to ensure the body is constantly supplied with oxygen and rid of carbon dioxide. It is an involuntary mechanism controlled by our respiratory center located in the brain, specifically in the medulla oblongata. However, it can also be temporarily controlled voluntarily, allowing us to alter our breathing rate or depth.