What mechanisms exist to assist with venous return to the heart in areas of rela

Question

What mechanisms exist to assist with venous return to the heart in areas of relatively low pressure?   What is compliance and Describe differences in compliance between the arteries and veins.   What influences the ability of blood to be pumped from areas of low pressure to high pressure (opposite of the movement expected based on the pressure gradient) when an individual is in the standing position?  

What adaptations does a giraffe have to assist with venous return across such long distances? What concerns exist when a giraffe bends its head down to drink water at a watering hole? What adaptations do giraffes have to address these concerns?

Explanation / Answer

The venous return is the rate of that flow of the blood to the heart it limits the cardiac output. The venous return to the heart from the venous vascular beds is pre-dominantly determined by a pressure gradient. The increase in venous pressure or decrease in right atrial pressure will increase the venous return .

The ability of hollow vessel to distend and to increase volume with increase in the pressure or the ability to resist recoil towards its orignal shape is called compliance in this process there is an increase in the volume in the vessel when the vessel pressure is increased. The venous compliance is approximately 30 times larger than the atrial compliance .

The effect of gravity on the venous return is paradoxial when a person stands up then the hydrostatic forces will result in the decrease of pressure in the right atrium and in the limb the venous pressure will increase . This increase the pressure gradient for venous return from the limbs to the right atrium because the cardiac output and the atrial pressure decreases and the flow through the systemic circulation false.

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