Get PUMPED

Hope you’re not tired of hearing my talking about blood and circulation, because surprise! Circulatory pathways! Specifically I want to show you how vertebrate circulation evolved from one simple circuit in early fish, to a dual circuit system in amphibians and mammals. To aid in explanation, I have provided my own diagrams (blame Medieval Musings).

First, fish circulation. Fish kind of suck at circulation (hush up, ichthyologists, you know it’s true). Yes, their two-chambered heart suits an aquatic lifestyle and a more “sophisticated” three- or four-chambered might be a weight burden, but it’s basically a double-ended turkey baster. It needs auxiliary “hearts” (blood vessels with pumping capabilities) and constant forward motion to keep things moving in the right direction. So yeah, sucky circulation. However, it is at least easy to understand: deoxygenated blood gets pumped from the heart, to the gills where it is oxygenated, then to the body and finally back to the heart when the blood has been deoxygenated again.

Amphibian circulation is…fine…I mean, nothing wrong with it! They even have dual circuit circulation and a three-chambered heart to provide the pressure needed to pump blood when motionless. It’s just…muddled. Probably because when the oxygenated blood leaves the lungs and enters the heart, it mixes with deoxygenated blood before being pumped out to the body. So the blood that provides oxygen to the body isn’t fully loaded with the stuff. Like cars in the carpool lane, some of them are packed with people and some of them are packed with people-sized things. The liars.

The biggest difference between mammal hearts and amphibian hearts is just a little tissue. But that extra tissue means a four-chambered heart and fully oxygenated blood pumping from lungs to heart to body.

OK, that’s all for circulation…for now.

Sources

-. 2010. GRE Subject Test: Biology 5th Ed. Kaplan, New York.

Sherwood, Lauralee, Hillar Klandorf and Paul Yancey. 2005. Animal Physiology: From Genes to Organisms. Thomson Brookes/Cole, Belmont, CA.

Baby, Get Your Blood Moving

Contrary to…whatever you thought before (if anything) your fetal blood circulation did NOT work like it does now. Because the lungs and associated blood vessels develop late, there are two shunts in place to counter the resistance this causes to the flow of blood. The first involves the foramen ovale, literally a hole between the left and right atria. The second is the ductus arteriosis, a small duct leading from the truncus pulmonalis (a pulmonary vessel) to the descending aorta. Both of these disappear in the weeks and months following birth.

Source:

Schöni-Affolter, Franziska, Christine Dubuis-Grieder, and Erik Strauch. “Embryo-Fetal Circulation System – Changes at Birth.” Human Embryology. Swiss Virtual Campus, 13 09 2006. Web. 17 Jan 2013. <http://www.embryology.ch/anglais/pcardio/umstellung01.html