Ventricular Septation and Outflow Tract Development in Crocodilians Result in Two Aortas with Bicuspid Semilunar Valves

Abstract

Background: The outflow tract of crocodilians resembles that of birds and mammals as ventricular septation is complete. The arterial anatomy, however, presents with a pulmonary trunk originating from the right ventricular cavum, and two aortas originating from either the right or left ventricular cavity. Mixing of blood in crocodilians cannot occur at the ventricular level as in other reptiles but instead takes place at the aortic root level by a shunt, the foramen of Panizza, the opening of which is guarded by two facing semilunar leaflets of both bicuspid aortic valves. Methods: Developmental stages of Alligator mississipiensis, Crocodilus niloticus and Caiman latirostris were studied histologically. Results and Conclusions: The outflow tract septation complex can be divided into two components. The aorto-pulmonary septum divides the pulmonary trunk from both aortas, whereas the interaortic septum divides the systemic from the visceral aorta. Neural crest cells are most likely involved in the formation of both components. Remodeling of the endocardial cushions and both septa results in the formation of bicuspid valves in all three arterial trunks. The foramen of Panizza originates intracardially as a channel in the septal endocardial cushion.

Normal and abnormal development of the aortic valve and ascending aortic wall: a comprehensive overview of the embryology and pathology of the bicuspid aortic valve

“…Evidently, these have a different physiology, being ‘cold-blooded’ as well as anatomy, as they present two aortas. Nevertheless, here the bicuspid valves function efficiently, even until advanced ages ( 58 ).…”

Myocardial development in crocodylians

“…Considering the fact that crocodylians are closely related to birds, 17 there is no wonder that also heart anatomy should be similar between these two groups. Nevertheless, there are some particular differences in gross heart morphology, such as presence of two aortic arches in crocodylians, 21 whereas birds have only the right aortic arch 35 . Another important difference is a specialized anatomical structure called foramen of Panizza placed between left and right aortic arches, and a cog‐tooth valve in the pulmonary artery 34 .…”

“…18 Moreover, anatomy of the crocodylian heart was studied for more than one century and it still stirs interest. [19][20][21][22][23] It was remarked that unlike the other reptiles, the crocodylian AV junction is only partially muscular in the dorsal part. 22 Christian and Grig documented by electrophysiological techniques presence of preferential electrical pathways on the sides of the interventricular septum reminiscent of bundle branches in Crocodylus johnstoni, 22 but could not find any morphological correlates for these pathways.…”

“…Therefore, there is a similarity in their hearts in terms of number of chambers as well 18 . Moreover, anatomy of the crocodylian heart was studied for more than one century and it still stirs interest 19‐23 . It was remarked that unlike the other reptiles, the crocodylian AV junction is only partially muscular in the dorsal part 22 .…”

Heart morphology during the embryonic development ofPodocnemis unifilisTrosquel 1948 (Testudines: Podocnemididae)

“…The functionality and significance of the cartilages at the base of the great cardiac vessels that make up the cardiac skeleton in adult individuals is still questioned and is usually linked to resistance, that is, the mechanical stresses that the septa and semilunar valves of the aorta and pulmonary artery are exposed to during intense cardiac cycle in reptiles. This suggests that mechanical stimulation in the region between the endocardial cushion at the base of the outflow tract and the aorticopulmonary septum during embryonic development may be a key factor in cartilage formation in vertebrate hearts (L opez et al, 2003;Poelmann et al, 2021).…”