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The veins act as a blood reservoir, because of the ease of distending them. 55-60% of blood is in systemic veins which is important for blood pressure. The volume of blood returned to the right atrium of the heart per minute is called the venous return. Generally venous return is equal to cardiac output, due to the closed system of the circulation, except for minor transient periods. A number of factors affecting the venous return are: Smooth muscle: Due to presence of smooth muscle, the diameter of the veins can be altered by sympathetic discharge(normally vasoconstrictive), adrenaline and angiotensin II (cause venoconstriction). But because the diameters of veins are large, venoconstriction has little effect on peripheral resistance. Elasticity of the heart: If the elasticity decreases, then the ability to fill the heart is reduced. valves: one way valves in the veins (not in large veins) ease blood flow to heart. Muscle pump: When muscles, particularly leg muscles contract, the thin walled veins are squeezed and the blood is forced towards heart, when muscles relax, blood enters the veins, but only from the arterial side. This is an important mechanism for facilitating venous return. Respiratory pump: Breathing in causes negative pressure in thorax causing a suction effect, i.e. the pressure gradient pushing blood towards the right atrium is increased, thus more blood returns to the heart, which means that inspiration leads to an increase in venous return. The opposite occurs with expiration, and venous return is decreased. Gravity: Opposes return of blood from the periphery during sitting or standing. The effect is lost when we lie down. Blood pressure at venous end of capillary: An increased pressure at the venule end of the capillary reduces venous return, because the pressure difference between the right atrium and the peripheral veins is reduced. Similarly a decrease in pressure at the venule end would increase venous return. Right atrial pressure: Is the inflow pressure for the heart. It is a function of the amount of blood returned to the heart and the pumping ability of the heart. Its value at rest is normally close to zero but can also become negative (between -4 to 5 mmHg). Its value is increased by blood volume, a weak heart, rapid increase in venous return. Its value is decreased by lower blood volume and a strong heart. The lower the pressure the greater the venous return (due to suction effect), but there is a limit to the increase in venous return because veins are collapsible.

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โˆ™ 2008-12-13 09:28:39
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Q: What does the venous return depend on?
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Related questions

What can cause venous return to the heart?

Inhale


What is the function of venous valves?

Valves aid in venous return by preventing the back flow of blood.


Tip the bed head down for venous return?

No, lift legs for venous return. Make sure legs are above heart. You do this for shock or bleeding.


How does the lymph return to the venous circulation?

Thoracic Duct


What increases stroke volume?

increase venous return


Where does the venous return from the heart enter?

The right atrium.


What would An increase in venous return do?

Increase venous returns increases end diastolic volume (EDV)


What increases venous return?

exhalation, the venous pump - muscle contraction, and sypmpathetic stimulation of the vascular bed


How does the venous return mechanism work?

pressure gradient , gravity , skeletal muscle pump, thoracic pump and cardiac suction would be the mechanisms for venous return.


Why the jugular venous pressure falls during inspiration?

because the endothoracic pressure is decreased and the venous return to the heart is increased.


What is return blood?

Return blood, most likely, refers to the venous blood that is returned to the heart.


What factor affecting stroke volume is determine by venous return?

contractility


What two things aide venous return within the body?

wht?


In which situation would the stroke volume be the greatest?

When venous return is increased


Lymph and venous blood flow are heavily depend on what?

the pumping action of the heart.


What is the medical term meaning abnormal circulatory condition characterized by decreased return of venous blood from the legs to the trunk of the body?

venous insufficiency


In addition to an inadequacy of circulating volume venous return and cardiac output are?

decreased


What medications decrease venous return reducing peripheral vascular resistance?

Vasodilators


What does contraction of veins do to the venous system?

Contraction of veins would increase venous return to the right atrium. It would increase the efficiency of the heart pumping.


What is the effect of exercise on venous return?

Venous return (VR) is the flow of blood back to the heart. Under steady-state conditions, venous return must equal cardiac output (CO) when averaged over time because the cardiovascular system is essentially a closed loop. Otherwise, blood would accumulate in either the systemic or pulmonary circulations.


How does gravity assist with venous return in the body?

Gravity does not assist in venous blood flow. If you really wanted gravity to help with venous blood flow you would have to hang in an inversion machine so you are upside down.


What will the venous return be if the cardiac output is 7.5 liters?

Venous return must always match cardiac output. So a CO of 7.5 l/m mill mean a VR od 7.5 l/m


Structure that return cerebrospinal fluid to the venous blood in the dural sinuses?

Arachnoid Villi


Who discovered that venous valves help aid in the return of blood to the heart?

William Harvey


What factors affect stroke volume?

Venous return controls EDV (end diastolic volume) and thus stroke volume and cardiac output. Venous return is dependent on: - blood volume and venous pressure - vasoconstriction caused by the sympathetic nervous system - skeletal muscle pumps - pressure drop during inhalation