Henry Family Blog

Venous return is the volume of blood flowing back to the heart from the systemic veins.  It depends on the pressure difference from the venules to the right atrium.  The pressure difference between the venous side to the right side of the heart is normally enough to drive blood back to the right side of the heart. 

Venous return also has two extra mechanisms; the respiratory pump and the muscle pump action.

Respiratory Pump:

During inhalation the diaphragm is pushed down and there is a pressure difference between the abdominal (high) to the thoracic cavity (low).  This drives blood back to the right side of the heart.

Muscle Pump Action:

Helps drive the blood back to the right side of the heart through a milking action.

The velocity of blood flow is inversely related to the CSA of blood vessels.  The velocity of blood flow is proportional to the volume of blood.  The velocity of blood flow decreases from the aorta to the arteries to capillaries and increases as it returns to the heart.  The aorta flows 40 cm/sec, capillaries flow 0.1 cm/sec.  An increase in CSA means a decrease in blood flow.  Capillaries have the highest CSA and the slowest blood flow.  This favors gas exchange at the capillaries. 

Neural Regulation of Blood Pressure:

The cardiovascular center signals the smooth muscles.  There are specific neurons that regulate vessel diameter. 

Baroreceptors monitor pressure in arteries to regulate blood pressure.  They are present in the carotid arteries, aortic arch, large arteries.  They also control postural changes.

Chemoreceptors monitor changes in blood (O2, CO2, H+)  Located in the same place as baroreceptors.  They are located in the aorta and the carotid arteries. 

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