Final answer:
The sympathetic nervous system responds to blood loss and decreasing arterial pressure by increasing heart rate, vasoconstriction, and the release of epinephrine and norepinephrine, which together work to raise blood pressure.
Step-by-step explanation:
When blood is lost and arterial pressure begins to fall, the sympathetic nervous system counters this decrease by activating mechanisms such as increased cardiac output and vasoconstriction. Baroreceptors in the aorta and carotid arteries detect the decrease in blood pressure and trigger a response that increases sympathetic stimulation. This leads to a rise in heart rate, often up to 180-200 contractions per minute, to restore cardiac output back to normal levels. Additionally, vasoconstriction of the arterioles increases vascular resistance, and constriction of the veins increases venous return to the heart, both of which help to raise blood pressure. The release of epinephrine and norepinephrine further enhances cardiac output and vasoconstriction.