diastole, systole, venous return and vascular shunt

Diastole

The relaxation of the heart after contraction to refill chambers with blood

Systole

The contraction of the chambers of the heart to pump blood

End Diastolic Volume

The volume of blood in the ventricle at the end of filling in diastole

End Systolic volume

The volume of blood in the ventricle at the end of contraction

Venous return

The volume of blood returning to the heart during each cardiac cycle

Venous Return mechanisms

The pressure of the blood in the large veins is very low and this makes it difficult to return blood back to the heart.

The large lumen of the vein offers little resistance to blood flow

• Pocket valve mechanism

• Skeletal muscle pump mechanism

• Respiratory pump mechanism

• Smooth muscle mechanism

• Gravity

Pocket valve mechanism

Valves prevent the backflow of blood

Skeletal pump mechanism

When the muscles contract and relax, they press on nearby veins causing a pumping effect and squeezing the blood towards the heart

Respiratory pump mechanism

When muscles contract and relax during inspiration and expiration process pressure changes occur in the thoracic and abdominal cavities

These pressure changes compress the nearby veins and assist blood return to the heart

Smooth muscle mechanism

a thin layer of smooth muscle in the veins helps squeeze blood back towards the heart

Gravity

Gravity helps the blood return to the heart from the upper body