How the breathing rate is kept within normal limits?
Several mechanisms work together to keep the breathing rate within normal limits:
1. Respiratory Center in the Brainstem: The respiratory center, located in the medulla oblongata and pons, is responsible for regulating breathing. It generates the basic rhythm and depth of respiration.
2. Chemoreceptors:
a. Central Chemoreceptors: Located in the medulla, these chemoreceptors monitor changes in the partial pressure of carbon dioxide (PaCO2) and hydrogen ion concentration (pH) in the cerebrospinal fluid (CSF). Increased PaCO2 or decreased pH stimulates the respiratory center to increase breathing.
b. Peripheral Chemoreceptors (Carotid Bodies and Aortic Bodies): These chemoreceptors are located in the carotid arteries and aorta, respectively. They sense changes in PaO2 (partial pressure of oxygen), PaCO2, and pH in the blood. When oxygen levels drop, PaCO2 rises, or pH decreases, these chemoreceptors send signals to the respiratory center to increase the breathing rate and depth.
3. Stretch Reflexes:
a. Hering-Breuer Reflex: This reflex prevents overinflation of the lungs. It involves stretch receptors in the airways that send signals to the respiratory center when lung volume increases excessively. This leads to a temporary cessation of inspiration, allowing for exhalation.
b. J-Receptor Reflex: This reflex is associated with the inflation of the lungs. It involves J-receptors located in the alveolar walls. When the lungs are inflated, these receptors send signals to the respiratory center, which leads to a slowing down of the respiratory rate.
4. Voluntary Control: To a certain extent, we can voluntarily control our breathing. This conscious effort can temporarily override the automatic mechanisms of breathing regulation, allowing us to hold our breath or breathe faster or slower for short periods.
These various mechanisms work in coordination to maintain the appropriate breathing rate to meet the oxygen and carbon dioxide requirements of the body, ensuring that the delicate balance of gases in our blood is preserved.