Final answer:
The baroreceptor reflex activates changes in sympathetic nervous system activity, heart rate, and total peripheral resistance, but not blood volume, within seconds to minutes. This is because blood volume changes occur via renal mechanisms over a longer timescale.
Step-by-step explanation:
The baroreceptor reflex is a rapid response mechanism primarily involving changes in the sympathetic nervous system activity, heart rate, and total peripheral resistance to stabilize blood pressure. However, it does not significantly alter blood volume within seconds to minutes of activation. This is because alterations in blood volume require renal adjustments over time through changes in the filtration and reabsorption rates, which are not immediate processes.
When blood pressure falls, for example due to blood loss, the baroreceptors trigger sympathetic responses that include an increase in heart rate (via increasing the strength of cardiac contractions) and vasoconstriction to raise pressure. Vasoconstriction, effected by the narrowing of blood vessels, increases total peripheral resistance and assists in elevating blood pressure.
Conversely, when pressure is too high, the baroreceptor reflex induces parasympathetic responses to decrease heart rate and dilate blood vessels, reducing resistance and pressure. In summary, blood volume is not altered in the short-term by this reflex.