As part of a blood drive on campus for the American Red Cross, you and your friends have just donated 500 ml of blood. You are now relaxing at the student lounge, waiting for A&P lab to begin. Unfortunately, even though you are thirsty, you haven't bothered to buy yourself a drink. Other than a little soreness of the skin and tissue around your median cubital vein, you feel fine. How has your 500 ml decrease in blood volume most likely affected your cardiac output, heart rate, and stroke volume?
A) no change in cardiac output, decreased heart rate, increased stroke volume
B) decrease in cardiac output, decreased heart rate, decreased stroke volume
C) increase in cardiac output, increased heart rate, increased stroke volume
D) no change in cardiac output, increased heart rate, decreased stroke volume

When a person donates blood, there is a slight loss of blood volume or hypovolemia. This triggers the baroreceptors of the blood; although does not trigger the osmoreceptor.

The baroreceptor responses are according to the arterial pressure which rises momentarily and results in increased sympathetic activity with decreased vagal activity.

These changes will lead to vasoconstriction, reduced stroke volume, increased heart rate or tachycardia which helps to maintain the cardiac output.

The soreness at the venepuncture site on the skin is due to bruising which is common after any needleprick. applying cold pack, elevating and resting the arm.

In order to compensate for the fluid volume loss and avoid dehydration, one must take plenty of fluids before and after blood donation.