3-year-old Sally decided to throw a temper tantrum, holding her breath, and stomping her feet. However, it is known that she can only hold her breath for a limited time before she will involuntarily begin to breathe again. Describe the feedback mechanism and anatomical structure that initiates involuntary breathing. Include how an increased level of CO2 affects this mechanism. For example, does pCO2 increase or decrease? Does pO2 increase or decrease? Does H+ concentration increase or decrease? What triggers Sallys respiration?