...and finally, my last circulation figure

 

This is from the same source as a previous post, being taken from Tortora's Principles of Anatomy and Physiology.

I conclude this series with a figure that differs from those I have posted previously. The only reference to anything anatomical here is to the lungs and capillaries. In so doing this figure raises the question of how to view the human circulation. Do we put the heart at the centre and follow the course of the blood it pumps out? If so, do we first follow it around the systemic circulation or the pulmonary? Or vice versa?

Or do we follow this approach? This figure follows the blood from its place of oxygenation to where that oxygen is delivered and back to where it gets oxygenated again. The heart takes on a more secondary role. Emphasis here is on the oxygen the circulation carries. (Not forgetting the place of carbon dioxide in all this.) The approach I used to take was very much akin to this. The emphasis here is on physiology rather than anatomy.

Coincidentally, this approach returns one to the idea of the simple closed circulation, not least that of fish from whence all forms of vertebrate circulation evolved. One might suggest that the human (mammalian) circulation is really just a single, simple loop that has been twisted into a figure of 8 (or ∞) with the heart at the crossing point.

Please be sure to click the label marked 'The Circulation' to access all related posts. My idea was to illustrate how the same topic can be illustrated in very different ways. View the others to see what I mean.