Question

The most important direct stimulus controlling the level of ventilation under normal resting conditions is

a) PaO2 detected by peripheral chemoreceptors

b) it depends on both central & peripheral chemoreceptors

c) pH detected by peripheral chemoreceptors

d) PaO2 detected by central chemoreceptors

e) pH of the CSF detected by central chemoreceptors

Answer 1

ANSWER IS OPTION E- pH of the CSF detected by central chemoreceptors

The most important factor controlling the rate and depth of breathing is the effect of carbon dioxide on the central chemoreceptors.

Carbon dioxide readily diffuses from the blood into the cerebrospinal fluid in the fourth ventricle.Here,carbon dioxide combines with water to form carbonic acid, which dissociates into hydrogenions and bicarbonate ions.

Most of the hydrogen ions within the cerebrospinal fluid are derived from this chemical reaction:

CO2 + H2O H2CO3 H+ + HCO3-

The hydrogen ions stimulate the central chemoreceptors, which send nerve impulses to therespiratory centers in the medulla. As carbon dioxide increases, so does the number of hydrogen ions, which in turn lowers the pH. Thecentral chemoreceptors actually respond to this pH changecaused by the blood PCO2