Control of Ventilation

CONTROL OF VENTILATION

While breathing can be controlled, it normally happens without thinking. The respiratory rate is the number of breaths per minute. Its rate can increase or decrease, depending on the condition. The medulla oblongata in the brain contains the respiratory center, which breathes at a rate that depends on the O2 level, the CO2 level, and the pH of the blood. The respiratory rate will vary with age, being between 30 and 60 breaths per minute prior to one year of age and about 12 to 18 breaths per minute in adulthood.

There are several factors that play into respiration. The medullary respiratory center sets the main breathing rhythm. The ventral respiratory group or VRG integrates the incoming data in order to set the breathing rhythm, while the dorsal respiratory group or DRG can integrate input from the different stretch receptors and chemoreceptors peripheral to the brain. The pontine respiratory group or PRG modifies and influences the function of the medulla oblongata. The pontine respiratory group is comprised of the pneumotaxic center and the apneustic center.

The hypothalamus monitors the body temperature and emotional state to regulate breathing. The aortic body and carotid body will monitor the pCO2 and pO2 of the blood as well as the pH. The cortical areas of the brain can control voluntary breathing. There are also proprioceptors in the joints and muscles that send impulses to the brain for increasing the respiratory rate with exercise. There are two reflexes: an irritant reflex that protects the lower airways from foreign bodies and an inflation reflex that protects the lungs from over-inflation.

The dorsal respiratory group or DRG maintains a constant breathing rhythm, while the ventral respiratory group or VRG is involved in forced breathing. The VRG stimulates the accessory muscles that are involved in the act of forced breathing. This results in forced expiration.

The pontine respiratory center or pontine respiratory group consists of a pair of nerve clusters in the apneustic center that stimulate the DRG in order to control the depth of breathing in deep breathing. The pneumotaxic center is a cluster of neurons that inhibit