Final answer:
The stroke volume decreases when blood volume decreases due to conditions like hemorrhage, leading to hypovolemia. The body compensates by increasing heart rate and contraction strength and through various mechanisms such as vasoconstriction and hormone release to maintain blood pressure.
Step-by-step explanation:
When blood volume decreases, for example, due to hemorrhage, the body experiences a condition called hypovolemia. This state can lead to a decrease in stroke volume (SV), which refers to the amount of blood the heart pumps out with each beat.
SV decreases when blood volume is reduced because there is less blood available to fill the heart before each contraction. If the blood volume drops significantly due to severe hemorrhage, the body's initial response is to compensate by activating baroreceptors that detect the reduction in blood pressure. These baroreceptors stimulate sympathetic responses, which can increase heart rate and the strength of heart contractions to maintain blood flow and blood pressure.
Treatments for hypovolemia typically include intravenous fluid replacement to restore the lost blood volume. Other responses to significant blood loss include the release of antidiuretic hormone (ADH) to stimulate vasoconstriction water recovery, and sympathetic stimulation leading to the release of epinephrine and norepinephrine, further enhancing cardiac output and vasoconstriction.