Peripheral chemoreceptors respond to hypoxia by oxygen sensitive:

Peripheral chemoreceptors are located in the aoic arch (aoic bodies) and at the bifurcation of the internal and external carotid aeries (carotid bodies). Peripheral chemoreceptors are especially impoant for detecting changes in O2 in the blood, although they also respond to a lesser extent to changes in CO2 and hydrogen ion concentrations. The chemosensitive cells of the carotid body are the type I or glomus cells. Surrounding individual clusters of glomus cells are the type II or sustentacular cells which are suppoing cells similar to glia. The central chemoreceptors detect changes in the H+ concentration (direct stimulus) of cerebrospinal fluid (CSF), including the brain interstitial fluid. The blood-brain barrier is relatively impermeable by H+ but it is very permeable by CO2. CO2 crosses blood brain barrier and forms H2CO3 that gives H+ ion on dissociation. The H+ concentration in brain interstitial fluid parallels the aerial Pco2 (secondary stimulus). Thus, the effects of CO2 on respiration are mainly due to its movement into the CSF and brain interstitial fluid, where it increases the H+ concentration and stimulates receptors sensitive to H+.