How can the cardiovascular system be closed if it takes up lymph?

[Trayshawn]

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Yeah, the cardiovascular system is supposed to be a closed system. That means it should not exchange matter nor energy with the outside environment.

One, its MAIN PURPOSE is to exchange matter with the environment (i.e. nutrients) and that alone precludes the possibility of being a closed system.

Second, even if you were to look passed this with some wave-handing answer along the lines of "well its not ALOT of exchange," you still run into the fact that the lymph system apparently dumps a bunch of its fluid into the circulatory system at the throacic duct.

So, from what I see, the cardiovascular system is just as open as the lymphatic system...
Right?!?!

 

[image187]

since when is the CV system a "closed system"? our volume status is constantly changing with regard to the amount of fluid. And when our kidneys filter the blood, we excrete free water, electrolytes, toxins, etc... With respect to RBC's and under normal conditions, I guess you can call it a "closed" system as these cells aren't supposed to be anywhere else, If it truly were a closed system, there could not be exchange with tissues

 

[Trayshawn]

thats what I'm saying! But look anywhere (textbooks, internet, professors) and they'll all say that we have a CLOSED circulatory system. What?!?!?

 

[NuttyEngDude]

It is considered closed because we have blood vessels as opposed to Insecta which have no capillaries or veins. Theirs is considered an open circulatory system. MCAT aside, if you have the opportunity, a class on Entomology is very fun. I even remember reading about the bombadier beetle in one of my mcat practice passages.