The main controlling agent for respiratory drive is which of the following –
Correct Answer: CO2
Description: Central chemoreceptors are situated in the deeper pa of medulla oblongata, close to the dorsal respiratory group of neurons. This area is known as a chemosensitive area, and the neurons are called chemoreceptors. Chemoreceptors are in close contact with blood and cerebrospinal fluid. Central chemoreceptors are connected with respiratory centers, paicularly the dorsal respiratory group of neurons through synapses. These chemoreceptors act slowly but effectively. Central chemoreceptors are responsible for 70% to 80% of increased ventilation through chemical regulatory mechanisms. Main stimulant for central chemoreceptors is the increased hydrogen ion concentration. However, if hydrogen ion concentration increases in the blood, it cannot stimulate the central chemoreceptors because the hydrogen ions from blood cannot cross the blood-brain barrier and blood-cerebrospinal fluid barrier. On the other hand, if carbon dioxide increases in the blood, it can easily cross the blood-brain barrier and bloodcerebrospinal fluid barrier and enter the interstitial fluid of the brain or the cerebrospinal fluid. There, carbon dioxide combines with water to form carbonic acid. Since carbonic acid is unstable, it immediately dissociates into hydrogen ion and bicarbonate ion. CO2 + H2O - H2CO3 - H+ + HCO3- Hydrogen ions stimulate the central chemoreceptors. From chemoreceptors, the excitatory impulses are sent to the dorsal respiratory group of neurons, resulting in increased ventilation (increased rate and force of breathing). Because of this, excess carbon dioxide is washed out and respiration is brought back to normal. Lack of oxygen does not have a significant effect on the central chemoreceptors, except that it generally depresses the overall function of the brain. Ref: Sembulingam - physiology 7th edition
Category:
Anaesthesia
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