Comparative Cardiovascular Anatomy Across the Amniota: Major Defining Features and Their Relevance to Anesthesia Research
In birds, reptiles and mammals, the atria are completely divided. With respect to the ventricles, categorization is not as straightforward. The order Crocodylia has a complete ventricular septum, as do the classes Aves and Mammalia. The remaining orders of the class Reptilia possess an incomplete ventricular septum. The conus arteriosus is completely divided into three trunks in the class Reptilia and is divided into two trunks in Aves and Mammalia. In the class Reptilia, the sinus venosus is distinct from the right atrium and in the Aves and Mammalia the sinus venosus has merged into the wall of the right atrium.1 In Amniota, embryos initially have a system of six aortic arches, but only arches III, IV, and VI persist, in altered form, into adults. The carotid system (common carotid, the external carotid, and the internal carotid arteries) arises from the aortic arch III. The pulmonary artery arises from aortic arch VI (caudal arch). The systemic arch (aorta) varies across vertebrate taxa. In birds, the aorta arises from the right aortic arch IV. In mammals, the aorta arises from the left aortic arch IV. Reptiles retain both the right and left aortic arch IV and thus have two aortas.2,4 The paths of these vessels vary in amniotes so the site of blood sampling will impact blood gas analysis. The intracardiac and extracardiac shunting of blood in Reptilia means that they differ from other amniotes in the way they uptake and distribute inhalant anesthetics.3
I would like to thank Dr. John Benson, Dr. Peter Constable, and Ms. Ragenia Sarr for their support of my research for my master’s thesis upon which this abstract is based.
1. Burggren, W., and D.A. Crossley. 2002. Comparative cardiovascular development: improving the conceptual framework. Comp. Biochem. Physiol. Mol. Integr. Physiol. 132:661–674.
2. Burggren, W.W., and S.J. Warburton. 1994. Patterns of form and function in developing hearts—contributions from nonmammalian vertebrates. Cardioscience. 5:183–191.
3. Eger, E.I. II. 1974. Anesthetic Uptake and Action. William A. Wilkins, Baltimore, Maryland Pp.1–146.
4. Kardong, K.V. 1998. The circulatory system. In: Kardong, K.V. (ed.) Vertebrates: Comparative Anatomy, Function, Evolution. WCB/McGraw-Hill, Boston, Massachusetts. Pp. 422–470.