Question

Discuss venous retrun. Be sure: to define venous return and explain the importance of venous return to cardiac output. What determines venous return? Discuss each way that venous return. Discuss each separately and make clear how each helps deterimine venous return.

Answer 1

Venous return is the flow of blood back to the heart. Since cardiac system is a closed loop, under normal condition venous return should equal cardiac output, if this dosent happen than it could mean that blood is accumulating either in the systemic circulation or pulmonary circulation.

According to Starling law of mechanism, If systemic venous return increases, than there is greater diastolic filling of the heart because of which cardiac muscle is stretched more, this in turn increases the force of contraction, this increases the stroke volume and cardiac output.

Factors that promote Venous return.

a) Increased activity of skeletal muscle pump.The veins are arranged in between the skeletal muscle fibers and are arranged parallel to skeletal muscle fibers. So when the muscle contracts the veins get squeezed. Due to the compressor effect of the muscle fibers on the vein, blood is made to flow through them.

b) Increased depth and frequency of respiratioin, respiratory pump. During inspiration, the intrapleural pressure becomes more negative. A simultaneous increase of pressure in the abdomen and a more negative pressure in thorax, increase the pressure gradient for flow of blood towards the heart from the abdomen.

c) Sympathetic mediated increase in venous tone, When the venomotor tone is increased, the capacity of veins decreases. This increases the venous return

d) Greater ease of blood flow from arteries to veins.

e) Posture and gravity. When gravitational force acts on the lower parts of body especially in the erect posture, it will decrease the venous return from the lower limbs.