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• As a byproduct of cellular metabolism,${\mathrm{CO}}_2$is constantly created in our cells. The majority ${\mathrm{CO}}_2$is transported to the lungs for removal, while the remainder dissolves in body fluids including plasma and saliva, generating carbonic acid.
• Bicarbonate is formed when carbonic acid dissociates. ${\mathrm{HCO}}_3^{-}$and ${\mathrm{H}}_3{\mathrm{O}}^{+}$are two examples. The kidneys supply more of the anion ${\mathrm{HCO}}_3^{-}$, resulting in an essential buffer system in the bodily fluid -${\mathrm{H}}_2{\mathrm{CO}}_3/{\mathrm{HCO}}_3^{-}$buffer.

${\mathrm{CO}}_2\left(g\right)+{\mathrm{H}}_2\mathrm{O}\left(l\right)↔{\mathrm{H}}_2{\mathrm{CO}}_3\left(\mathrm{aq}\right)↔{\mathrm{H}}_3{\mathrm{O}}^{+}\left(aq\right)+{\mathrm{HCO}}_3{}^{*}(aq)$

• Excess ${\mathrm{H}}_3{\mathrm{O}}^{+}$in the bodily fluids reacts with $\mathrm{HCO}3$- and excess$\mathrm{OH}$- interacts with carbonic acid.

${\mathrm{H}}_2{\mathrm{CO}}_3\left(aq\right)+{\mathrm{OH}}^{-}\left(aq\right)→{\mathrm{H}}_2\mathrm{O}\left(l\right)+{\mathrm{HCO}}_3^{-}\left(aq\right)$

• Carbonic acid content in the body is directly related to the partial pressure of ${\mathrm{CO}}_2$
  

• When we hold our breath, the${\mathrm{CO}}_2$level in our bodies rises, increasing $\left[{\mathrm{H}}_2{\mathrm{CO}}_3\right]$, the equilibrium shifts to create more ${\mathrm{H}}_3{\mathrm{O}}^{+}$, lowering the value of $\mathrm{pH}$.

$\mathrm{pH}=-\log \left[{\mathrm{H}}_3{\mathrm{O}}^{+}\right]$

${\mathrm{H}}_3{\mathrm{O}}^{+}?\mathrm{pH}?$

• As a result, the blood's $\mathrm{pH}$ decreases as you hold your breath.