The heart of the South American rattlesnake, Crotalus durissus

Abstract

Most anatomical and physiological studies of the sauropsid heart have focused on species with extraordinary physiologies, and detailed anatomical descriptions of hearts from sauropsids with more common physiologies are therefore warranted. Here, we present a comprehensive study of the cardiac anatomy of the South American rattlesnake (Crotalus durissus). The cardiovascular physiology of this species has been investigated in a number of studies, whereas only a few cursory studies exist on the cardiac anatomy of viperid snakes. The heart of C. durissus is typically squamate in many regards. Both atria are thin-walled sacs, and the right atrium is the most voluminous. The single ventricle contains three major septa; the vertical septum, the muscular ridge (MR), and the bulbuslamelle. These partially divide the ventricle into three chambers; the systemic and left-sided cavum arteriosum (CA), the pulmonary and right-sided cavum pulmonale, and the medial cavum venosum (CV). The MR is the most developed septum, and several additional and minor septa are found within the CA and CV. An extraordinary thin cortical layer encloses the ventricle, and it is irrigated by a remarkably rich arborization of coronary arteries. Previous studies show high degrees of blood flow separation in the Crotalus heart, and this can only be explained by the coordinated actions of the septa and the prominent atrioventricular valves.

Ablation of the ability to control the right-to-left cardiac shunt does not affect oxygen consumption, specific dynamic action or growth in rattlesnakes,Crotalus durissus

“…The South American rattlesnake, C. durissus, normally exhibits a variable intracardiac shunt, which is consistent with its ventricular anatomy, that allows oxygen-poor blood from the right atrium to be ejected into one of the two aortic arches (Jensen et al, 2010a). adjustments in cardiac shunting.…”

“…Nevertheless, factors other than changes in vascular resistances may influence the shunt pattern (see Hicks, 1993;Hicks and Wang, 1998). For example, 'washout' of the cavum venosum during cardiac systole provides a small fraction of systemic venous blood to the systemic circulation, resulting in an additional R-L shunt (Hicks, 1993;Jensen et al, 2010a). In contrast, during the subsequent diastole, pulmonary venous blood within the cavum venosum 'washes' into the pulmonary circulation, accounting for an additional L-R shunt (see Hicks, 1993).…”

The Functional Significance of the Reptilian Heart: New Insights into an Old Question

“…Thus, the MR is particularly large in pythons and varanid lizards, where it provides pronounced separation of the CP from CV/CA during ventricular systole allowing for much higher systemic pressures than pulmonary arterial pressures (see Jensen et al 2010b, c ) . While the MR may also appear rather large in several other snakes, such as rattlesnakes and anaconda, there is no evidence of ventricular pressure separation in other snakes than pythons (Jensen et al 2010a ) . In testudines, the MR is often smaller than in squamates and the volume of the CV is larger.…”

Vagal tone regulates cardiac shunts during activity and at low temperatures in the South American rattlesnake, Crotalus durissus

“…In the present study, we investigate whether the vagus actively regulates cardiac shunt patterns in South American rattlesnakes (Crotalus durissus Linnaeus 1758). This species possesses a typical reptilian heart (Jensen et al 2010), but only the left branch of the vagus controls the smooth muscle of its single pulmonary artery (Taylor et al 2009). Hence, unilateral left vagotomy abolishes the control of G pul without affecting regulation of heart rate (f H ), which is maintained via the right vagus (Leite et al 2013;Taylor et al 2009).…”