Chemical Regulation of Breathing

Chemical Regulation of Breathing is part of the involuntary (autonomic) control of breathing.

Chemoreception
* central chemoreceptors * peripheral chemoreceptors
 * detects arterial partial pressure of CO2 (PCO2) and pH;
 * increase in alveolar PCO2 (PaCO2) causes ventilation to rise;
 * PO2 normally stimulates ventilation when it falls below ~8kPa. when the fall is accompanied by an increase in PCO2, the increase in ventilation is greater;
 * has two pathways:

Central Chemoreceptors
* an increase in blood PCO2 makes a CSF more acid * increases ventilation that will lead to less CO2
 * near the ventrolateral surface of the medulla;
 * responds indirectly to blood PCO2, via H+ but not to PO2;
 * CO2 diffuse across blood-brain barrier from blood to Cerebral Spinal Fluid (CSF), but H+ and HCO3- (bicarbonate) does not;
 * pH of CSF is determined by arterial PCO2 and CSF HCO3-:
 * are responsible for ~80% of the response of CO2;
 * are not affected by blood pH because of the H+ impermeability.

how central chemoreceptors are stimulated by an increase in arterial PCO2?
 * because CO2 that is in the blood capillary will pass the blood CSF barrier and in the CSF will react with water (H20) to make bicarbonic acid (H2CO3), that will spilt into HCO3- and H+
 * this H+ will send stimulus to chemoreceptor neurons in medulla oblongata

Peripheral Chemoreceptors
* increase in initiation of dopamine (neurotransmitter) * increase in impulses to respiratory center * increase in ventilation
 * respond to changes in low PO2 and pH;
 * located in carotid and aortic bodies, that have neuro-epithelial cells that contact with sensory nerve terminals;
 * when potassium (K+) channels close, calcium (Ca+) open and:
 * is responsible for ~20% of the response to the increase in PCO2;
 * increases in [H+] stimulates ventilation.