ANATOMY

Detailed explanation-1: -Gravity helps the blood return to the heart from the upper body. When muscles contract and relax, they press on nearby veins, causing a pumping effect and squeezing the blood towards the heart. A thin layer of smooth muscle in the veins helps squeeze blood back towards the heart.

Detailed explanation-2: -During upright posture, skeletal muscles help maintain venous return and consequently cardiac output by compressing underlying veins in order to increase blood flow back to the heart (skeletal muscle pump).

Detailed explanation-3: -Venous return is facilitated by a number of factors, including inspiration, increased total blood volume, increased venomotor tone, the cardiac suction effect, the presence of venous valves and the skeletal muscle pump.

Detailed explanation-4: -The skeletal muscle pump or musculovenous pump is a collection of skeletal muscles that aid the heart in the circulation of blood. It is especially important in increasing venous return to the heart, but may also play a role in arterial blood flow.

Detailed explanation-5: -Respiratory Activity (Abdominothoracic or Respiratory Pump) Respiratory activity affects venous return through changes in right atrial pressure, which is an important component of the pressure gradient for venous return.