What is respiratory rate and how is it controlled?

Respiratory rate refers to the number of breaths taken per minute. In medical terms, it is the number of times the chest rises (inhalation) and falls (exhalation) in a given period. It is an important vital sign that indicates how efficiently the respiratory system is functioning. The normal respiratory rate for adults is 12-20 breaths per minute, while for infants, it ranges from 30-60 breaths per minute.

Respiration is the process by which living organisms exchange gases, primarily oxygen and carbon dioxide, between their internal environment and the external environment. Respiration in humans takes place through a series of processes: 1. Inhalation: The diaphragm (a muscle below the lungs) and the intercostal muscles (between the ribs) contract, expanding the chest cavity and causing air to flow in through the mouth/nose and down the trachea. 2. Gas exchange: Oxygen from the inhaled air diffuses across the thin walls of the alveoli (air sacs) in the lungs and into the bloodstream, where it binds to hemoglobin in red blood cells. Simultaneously, carbon dioxide diffuses from the bloodstream across the alveolar walls and into the alveoli. 3. Exhalation: The diaphragm and intercostal muscles relax, the chest cavity contracts, and carbon dioxide-rich air is expelled from the lungs through the trachea and out of the mouth/nose.

The respiratory rate is controlled by the respiratory center, located in the medulla oblongata of the brainstem. This center receives input from various sources, such as chemo- and mechanoreceptors, and adjusts the respiratory rate accordingly. There are three main factors that influence the control of respiratory rate: 1. Blood carbon dioxide levels: Chemosensitive neurons in the medulla monitor the pH of the cerebrospinal fluid, which is primarily determined by carbon dioxide levels. If carbon dioxide levels rise, the pH decreases, triggering the respiratory center to increase the respiratory rate to remove excess carbon dioxide. 2. Blood oxygen levels: Peripheral chemoreceptors located in the carotid and aortic bodies monitor blood oxygen levels. If oxygen levels drop, these receptors send signals to the respiratory center to increase the respiratory rate to obtain more oxygen. 3. Physical activity: Mechanoreceptors in the muscles and joints signal the respiratory center in response to changes in physical activity. When physical activity increases, the respiratory center increases the respiratory rate to meet the enhanced oxygen demand and carbon dioxide removal needs. In summary, respiratory rate is the number of breaths taken per minute and is an essential vital sign in humans. It is controlled by the respiratory center in the brainstem, which receives and processes information from various receptors, adjusting the respiratory rate based on factors such as blood carbon dioxide and oxygen levels, and physical activity.