How is blood pressure maintained in veins to counter the force of gravity?
A) Blood pressure is maintained in veins because the heart pumps blood through the veins.
B) Blood pressure is maintained in veins because the valves reduce the flow of blood as blood passes by.
C) Blood pressure is maintained in veins by the contractions of surrounding skeletal muscles that squeeze venous blood toward the heart and the presence of valves which prevent backflow of the blood.
D) Blood pressure is maintained in veins by using the valves as pumps to push blood back toward the heart.
E) Blood pressure is maintained in veins by contractions of the smooth muscle in the walls of the veins that squeeze venous blood toward the heart and the presence of valves which prevent backflow of the blood.
Answer: C
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In the final step of enzymatic catalysis,
A. the substrate is released and the enzyme is inactivated. B. the product is completed and the enzyme is inactivated. C. the products are released and the enzyme is free to bind other substrates. D. the enzyme and substrate form chemical bonds with each other resulting in a new product. E. equilibrium is obtained so that the enzyme does not catalyze further reactions.
Which lymph organ lies in the mediastinum?
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