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In a closed circulatory system, all of the blood stays within blood vessels or the heart itself. Organisms that have open circulatory systems, such as arthropods, have hemolymph (a fluid that is essentially a mixture of blood and interstitial fluid). The hemolymph actually does travel in vessels for a very short amount of time, as it is leaving the heart. ...


I think none. It is so specific frequency range that the possible sources are autonomic nervous system and some reflex arch. Also, the frequency is logically low with autonomic triggering. My conjecture is that sympaticus starts up extrasystoles. I think it must go through some reflex arch to be so specific.


Extension to Doctor Whom's clear answer. Clearer problem It is debated whether the pathophysiology of IST and POTS results from abnormal autonomic regulation or abnormal sinus node function. Radiofrequency Catheter Modification of the Sinus Node for “Inappropriate” Sinus Tachycardia Location modification: Superior aspect of the crista terminalis. ...


The SA node is not necessary for contraction of the heart. The reason that this works is exactly what you mentioned: schematics. They are in sequence, but within that sequence, there are multiple autonomous signal generators in the heart, where spontaneous depolarization occurs to initiate contraction: the SA node, the AV node, and the purkinje fibers. ...

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