During exercise, the demand for oxygen increases for use in cellular respiration, the process that produces energy in the body's tissues. A coordinated response between lungs and heart allows for an increase in oxygen available to the body's tissues and the removal of carbon dioxide, the waste product of cellular respiration.
Breathing Rate Changes
During exercise, the volume of air moving through the lungs can increase from 2.46 liters to 80 liters per minute through faster and deeper breathing. According to the American Physiological Society, the breathing rate for an adult at rest is 12 to 20 breaths per minute, and after exercise the breathing rate can increase to 40 breaths per minute. According to MedlinePlus.com, the effect of exercise on breathing rate of an older adult does not change even though lung function decreases slightly.
Control of Breathing Rate
The breathing rate at rest is controlled by the nervous system. The brain monitors the concentrations of oxygen and carbon dioxide in the blood. During exercise, the body uses more oxygen to produce energy in muscles and other tissues. A decrease in oxygen concentration or an increase in carbon dioxide concentration in the blood signal a need for additional oxygen. As an immediate response, the autonomic nervous system increases the breathing rate and adjusts the heart rate to increase blood flow throughout the body.
Lung Capacity
The lungs expand to take in fresh air containing oxygen. According to "Pulmonary Function and Respiratory Regulation," approximately one tenth of lung capacity is used during rest, leaving reserve capacity to meet the need for increased oxygen flow during exercise. To meet the additional need for oxygen during exercise, the breathing rate increases, along with the volume of air in the lungs.
Gas Exchange
The increased volume of air in the lungs during exercise makes more oxygen available to replace depleted oxygen in the tissues. The heart pumps blood into the lungs, where a gas exchange occurs; excess carbon dioxide leaves the blood and oxygen enters the blood. The oxygenated blood is then delivered to all tissues in the body. According to the American Physiological Society, normally 1.5 percent of oxygen gas is dissolved in the blood and 98.5 percent of oxygen in the blood is combined with hemoglobin protein.
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