You've been sitting cross-legged on the floor of your dorm room while studying. As you stand up to go get a snack, you realize that you've lost feeling in one of your feet. A minute later, all feeling is restored. Being a physiology student, you understand that blood flow was occluded during the time that you were sitting, and that blood flow was restored as you stood up. What else is TRUE?
A. The resistance of the blood vessels did not change from sitting to standing, but gravity helped in blood flow.
B. High levels of built up CO2 acted as vasoconstrictors in the foot's blood vessels.
C. The decreased oxygen content of the foot tissues and the increased levels of metabolic wastes both acted as vasodilators, increasing the flow of blood through the tissues upon standing.
D. As you stood, vasoconstriction occurred in the foot's blood vessels to protect them from shock.
E. All of these are true.
Answer: C
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