Which of the following mechanisms facilitate venous return to the ...

[javeds]

Which of the following mechanisms facilitate venous return to the heart? 1. Sodium/potassium pump 2. Sympathetic venomotor tone 3. Cardiac suction 4. Skeletal muscle contraction
 
  a. 1 and 2 only
  b. 2, 3, and 4 only
  c. 1, 2, 3, and 4
  d. 3 and 4 only

Question 2

Why are the vessels of the venous system, particularly the small venules and veins, termed capac-itance vessels?
 
  a. They transmit and maintain the head of perfusion pressure.
  b. They can alter their capacity to maintain adequate perfusion.
  c. They determine the afterload on the left ventricle.
  d. They maintain a constant environment for the body's cells.

[mbcrismon]

Answer to Question 1

ANS: B
The following four mechanisms combine to aid venous return to the heart: (1) sympathetic ve-nous tone, (2) skeletal muscle pumping, or milking (combined with venous one-way valves), (3) cardiac suction, and (4) thoracic pressure differences caused by respiratory efforts.

Answer to Question 2

ANS: B
By quickly changing its holding capacity, the venous system can match the volume of circulating blood to that needed to maintain adequate perfusion. Accordingly, the components of the venous system, especially the small, expandable venules and veins, are termed capacitance vessels.

[javeds]

Excellent

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