Final answer:
The normal breathing rate for an adult is 12 to 20 breaths per minute, decreasing from higher rates in infancy and childhood, and is regulated by the respiratory center in the brain.
Step-by-step explanation:
The normal breathing rate for an adult is 12 to 20 breaths per minute. The respiratory rate can vary depending on several factors, such as age, physical activity, and overall health. Infants have a much higher respiratory rate; for instance, a child under 1 year may demonstrate a normal respiratory rate ranging from 30 to 60 breaths per minute. As children grow older, this rate gradually decreases, with a typical range of 18 to 30 breaths per minute around the age of 10. By the time they reach adolescence, their respiratory rate is closer to the adult range. The regulation of respiratory rate is critical; it ensures sufficient alveolar ventilation, which allows for proper gas exchange and prevents the buildup of carbon dioxide in the alveoli.
The control of breathing is involuntary, managed by the respiratory center within the medulla oblongata in the brain, which responds to changes in carbon dioxide levels, oxygen levels, and the pH of the blood. The respiratory center ensures that the breathing rate maintains the body's required levels of oxygen, while also removing carbon dioxide efficiently.