CV physiology question regarding distribution of bloodflow

[Thyroxine]

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Hey guys

In my notes I have the following percentages for distribution of blood in the circulation at rest:

Capillaries - 5%
Arterioles and arteries - 11%
Heart and lungs - 17%
Veins - 67%

My question is this: why is 2/3rds of the blood distributed in the veins? Is it because they are the most compliant vessels?

Thanks 🙂

 

[Jonari]

Hey guys

In my notes I have the following percentages for distribution of blood in the circulation at rest:

Capillaries - 5%
Arterioles and arteries - 11%
Heart and lungs - 17%
Veins - 67%

My question is this: why is 2/3rds of the blood distributed in the veins? Is it because they are the most compliant vessels?

Thanks 🙂

Yup, the veins are much more compliant than the arteries, since they lack the muscular layer to contract back, when stretched. This also explains why when a person is losing too much blood (ie hemorrhage) the decreased blood flow/pressure is sensed by the carotid bodies/aortic bodies, and send a signal to the medulla, to decrease vagal tone and increase sympathetic tone. The alpha1 receptors found on the vessels will contract. The blood will then go from the veins into systemic circulation, to help and try to maintain the CO and HR during initial blood loss.

In add'n this is also why when we're doing a blood transfusion, it's done really slowly. If it were done too fast, the body would sense this, and all the blood would get pooled up within the veins. I hope what I wrote helps.

 

[Thyroxine]

Yup, the veins are much more compliant than the arteries, since they lack the muscular layer to contract back, when stretched. This also explains why when a person is losing too much blood (ie hemorrhage) the decreased blood flow/pressure is sensed by the carotid bodies/aortic bodies, and send a signal to the medulla, to decrease vagal tone and increase sympathetic tone. The alpha1 receptors found on the vessels will contract. The blood will then go from the veins into systemic circulation, to help and try to maintain the CO and HR during initial blood loss.

In add'n this is also why when we're doing a blood transfusion, it's done really slowly. If it were done too fast, the body would sense this, and all the blood would get pooled up within the veins. I hope what I wrote helps.

Thanks very much, it most certainly did help 🙂

 

[Jonari]

Thanks very much, it most certainly did help 🙂

Just one more example, which I think is better than the examples above. When you give a patient venodilator (ie nitroglycerin), these drugs work more so on the venous circulation. Dilatation of these vessels, leads to pooling of the blood within the venous circulation, and by doing this, this decreases the overall preload on the heart, and the ventricles don't need as much oxygen to push the blood flow forward. Hence, why nitrates are given for a patient that has stable angina.