Respiratory Physiology Lecture 7 Part 31: More on Chemical Control of Respiration

Question 1

Central Chemoreceptors

Answer 1

• Central chemoreceptors are located in the medulla oblongata of the brainstem. They detect changes in the arterial partial pressure of carbon dioxide (pCO2). When changes are detected, the receptors send impulses to the respiratory centres in the brainstem that initiate changes in ventilation to restore normal pCO2.
• Central chemoreceptors are specialized neurons located close to the ventral surface of the medulla (Close contact with blood vessels and cerebrospinal fluid)
  
  • Rostral, intermediate, caudal regions
• Other chemosensitive sites are in the medullary raphe, hypothalamus

Question 2

How does CO2 effect chemoreceptors?

Answer 2

CO2 will diffuse from the capillary to the Extracellular space in brain and will tend to interact with water and produce H+ ions. (Similar to what happens in RBCs). The increase in H+ ions is excitatory factor or stimulus for the activation of these neurons. Will act similar to glomus cells and provide excitatory impulse to respiratory cells

Question 3

Pathway Response to Hypercapnia Mediated by Central & Peripheral Chemoreceptors

Answer 3

Question 4

Hypercapnia

Answer 4

Hypercapnia is the elevation in the partial pressure of carbon dioxide (PaCO2) above 45 mm Hg

Question 5

primary response to hypercapnia

Answer 5

Central chemoreceptors are responsible for 70 % of response to hypercapnia

• Again, response to hypercapnia is mediated by effects at the level of dorsal and ventral respiratory group that change ventilation

Question 6

Respiratory Response to Metabolic Acidosis

Answer 6

Lactic acid accumulation during strenuous exercise → peripheral chemoreceptors → hyperventilation

• Accumulation of lactic acid during strenuous exercise with reduces pH or increase H+ concentration. Will activate peripheral chemoreceptors that will drive ventilation to increase and will have return of H+ toward normal levels.
• H+ stimulates mostly peripheral chemoreceptors because H+ does not cross easily blood brain barrier (As CO2 does)