How do buffer systems react to low/high pH in the blood?

The general function of a buffer system is to prevent rapid & wide swings of pH. When the body's buffer system is overstressed, then the pH will get too far from the typical normal pH of 7.4

The body has 2 ways to buffer swings in pH - respiratory, which reacts rapidly, and metabolic, which is slower to respond but is 'permanent'. The respiratory system can change pH rapidly through hyper/hypo ventilation but if the metabolic system can not maintain the change, things start to fall apart. If the body pH drops below 6.8 or so, death is not far behind. Too high is less likely but can also cause death.

Note: 7.0 is neutral pH. Normal human pH is slightly alkaline.

What ions? - the body's pH is maintained by the equilibrium of acidic & basic molecules, mostly HCO3 & CO2 and also Phosphorus related buffers. Hydrogen ions get exchanged back & forth. Too many H+ ions tends to lower the pH (more acidic), too few raised the pH - more alkaline.

Lactic acid build up - as the name implies - lowers the pH of the body and the body pH becomes more acidic.

How breathing changes -

The body needs to compensate for the lower pH that results from increase lactic acid. The most rapid mechanism that responds is the respiratory system by hyperventilation. This removes quantities of CO2 thereby increasing the overall pH. But this shift is transient since the body constantly produces CO2. Then the buffer system must come into play for a more 'permanent' fix to the decreased pH. If the body does not have enough stored HCO3 (Bicarb) or HPO4 (Phosphate), then a metabolic problem begins.