Some homeostatic imbalances cause a variable that is normally controlled by negative feedback to be abnormally controlled by positive feedback. True or false?

True

Explanation:

Some deviations from normal homeostasis activate the positive feedback loops to control the conditions which are otherwise regulated by negative feedback mechanisms.

For example, the blood levels of respiratory gases and H + ions are regulated by a negative feedback system via chemoreceptors. The increased partial pressure of carbon dioxide gas and lowered pH or lowered partial pressure of oxygen in the blood are sense by central and peripheral chemoreceptors which in turn activate the neurons of the dorsal respiratory group (DRG).

The activated DRG triggers an increased in the rate and depth of the breathing to facilitate the inhalation of more oxygen and exhalation of CO2 to restore the normal levels.

However, hypocapnia inactivates the chemoreceptors and does not allow negative feedback to restore the normal CO2 levels in the blood.

Under such conditions, the positive feedback loop stimulates the DRG neurons more strongly in response to the increased partial pressure of CO2 above the normal levels than when the partial pressure of oxygen falls below the normal level. These dangerously lowered oxygen levels may also cause fainting.