Circulation in organisms before the full development of the heart
The article, "Impedance defined flow: generalization of William Harvey's concept of the circulation - 370 years later" by Moser M, Huang J W, Schwarz G S, Kenner T, and Noordergraaf A, in the International Journal of Cardiovascular Medicine and Science, Vol. 1, No. 3/4, 205-211 1998, provides some light on the issue of how circulation takes place in the circulatory system of embryos before the development of the heart. Full article [683K].

It discusses the relation between flow and the existence of valves in circulatory systems and points to and demonstrates the existence of valve free circulation in both mechanical and biological systems.

ABSTRACT:

"William Harvey (1628) attributed the flow of blood through the cardiovascular system to the heart, providing the energy, and to its valves, ensuring the preferential direction of flow. This report presents a flow generating mechanism free of valves, dubbed impedance defined flow. 

"Nature offers examples where impedance defined flow appears to be the sole perfusion mechanism. These include the human foetus by the end of the third week of gestation. It proposes that addition of valves in specific locations is a later development in evolution and amounts to a special case of impedance flow, a suggestion that may profoundly impact our current concept of the circulation. 

SUMMARY:

"It is shown that the impedance defined flow principle, introduced in this paper, is capable of producing average flow. Any compliant fluid conducting system of which a part is subject to pressure oscillation, and which displays assymetric flow impedances tends to produce unidirectional flow. This constitutes a generalization on Harvey's view that blood moves around the circuit solely by the pumping action of the heart, thereby creating a new field of research within and without the cardiovascular system. Judicial placement of the valve can improve the pumping efficiency of the system. 

"The fact that valveless circulatory systems can be found predominantly in simpler animals suggests that valves constitute a refinement developed later in the evolutionary process. Also, in early development, valves appear only after the creation of flow in the embryonic circulation giving rise to the suggestion, that flow contributes to the location and formation of the valves." Copyright 1998: Medical and Engineering Publishers, Inc.

In general this article supports, as one example, what was pointed to already in 1894 by an Austrian physician, who described the hydraulic ram as a more appropriate model of the function of the heart than the pump model. 

Twenty-six years later, this view was brought forward again by Rudolf Steiner in a lecture as part of a series of lectures on medicine, leading to the foundation of anthroposophical medicine, pointing in the direction of the understanding of Aristotle of the heart, not primarily as a "will" organ, but as a "sense" organ.

The general intermediary nature of the heart in the human organism points to a degree of onesidedness in both perspectives.

For more on Rudolf Steiner's view of the heart in the human being, see a lecture.

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Copyright 2004-2006: Robert Mays and Sune Nordwall