Comparative cardiac anatomy of the reptilia. I. The chambers and septa of the varanid ventricle

Abstract

Examination of the cardiac anatomy of lizards of the family Varanidae revealed that much of the previous literature contained basic errors both in description and interpretation. These are corrected and terminology of various authors is standardized.The varanid ventricle is similar to that of most other lizards in not being elongated, in having the base at right angles to the longitudinal axis, and in having the vertical septum weakly developed. However, it is not a typical lacertilian heart in that it has a number of characteristic ophidian features such as a muscular cone surrounding the cavum latero-dorsale and a prominent twisting of the cava. It lacks a gubernaculum cordis and a cartilaginous rod in the septum aortico-pulmonale, both of which are present in many non-varanid lizards, but seldom occur in snakes. The location of the heart is more posterior in the body than is true of other lizards.During preliminary investigations on reptilian cardiac physiology, it became apparent that there exists no clear understanding of basic squamate heart anatomy requisite for interpretation of experimental results. Sources of confusion have been ( 1 ) failure to standardize terminology and inconsistent and incorrect usage of terms, (2) improper orientation of materials, slides and/or drawings being examined or presented up-side-down and misinterpreted accordingly, and ( 3 ) an uncritical following of the mistakes of previous authors. Webb ('69) presented a partial review of the literature, standardized terminology, and by re-examining hearts of the species upon which much of the anatomical literature is based, corrected many previous errors. A series of papers, of which this is the first, expands and revises that study. The present one treats the ventricle of the lizards of the family Varanidae. This family was selected first, because: (1) It belongs to a group (Platynota) claimed to be ancestral to the ophidian line (but see reviews by Bellairs and Underwood '51, McDowell and Bogert '54), so that an understanding of the anatomy of varanids J. MORPH., 134: 335-350. may be important for phylogenetic interpretations. ( 2 ) Much of the previous literature has been based on this family and correction of previous erroneous interpretations of varanid cardiac anatomy also clears up a number of problems related to the general structure of the squamate heart. ( 3 ) The varanid heart has been used as a "typical" squamate heart (see Literature below). This unwarranted assumption must be disposed of before proceeding with further comparative studies.The ventricle is emphasized because most of the confusion in the literature centers around this part of the heart. THE GENERALIZED SQUAMATE VENTRICLEThe ventricle is typically conical with the apex directed posteriorly. In most lacertilians, it lies in the midline of the body with the bulbar region facing ven- 335

The role of the sarcoplasmic reticulum in the generation of high heart rates and blood pressures in reptiles

“…In support of this contention, SR-dependent fish, such as tuna, generate higher arterial blood pressures than other fish (Farrell, 1996;Vornanen et al, 2002). Increased force of contraction and systemic pressures are primarily accomplished by thickening the ventricular wall (Webb et al, 1971;Farrell et al, 1998), and if this is achieved via myocyte hypertrophy, the diffusional distance for Ca 2+ movement will be increased which may require more efficient Ca 2+ cycling, possibly via the SR. As with fish and mammals, reptilian atrial tissue was generally more sensitive to SR inhibition than ventricle strips (Aho and Vornanen, 1999;Keen et al, 1992;Shiels et al, 1999;Bers, 2001;Mercier et al, 2002). These findings correlate with ultrastructural and biochemical studies showing higher SR densities and SR associated proteins in atrial vs ventricular muscle (Minajeva et al, 1997;Bossen et al, 1981;Luss et al, 1999).…”

Ventricular haemodynamics inPython molurus: separation of pulmonary and systemic pressures

“…Webb et al, 1971;Webb, 1979). The vertical septum is large and separates the CA from the left side of the heart.…”

“…Detailed anatomical descriptions of the ventricle of Python are, unfortunately, not available, but the structural similarities between varanid lizards and ophidians have been noted numerous times for more than a century (e.g. Jacquart, 1855;Robb, 1965;Webb et al, 1971Webb et al, , 1974Webb, 1979;van Mierop and Kutsche, 1985;Farrell et al, 1998). Thus, as in Varanus, the ventricular wall surrounding the CA of Python molurus is much thicker than the wall surrounding the CP and the CA is extensively trabeculated compared to the CP T.…”

How the python heart separates pulmonary and systemic blood pressures and blood flows

“…Function of the python heart pulmonary chamber (cavum arteriosum and cavum pulmonale, respectively), with a third shallow chamber, the cavum venosum, situated between the other two. Three different septa are responsible for this division and while all three are found in the ventricle of all squamates and testudines, they are particularly conspicuous and well developed in the heart of pythons and varanid lizards (Greil, 1903;Acolat, 1943;Webb et al, 1971;Webb, 1979;Van Mierop and Kutsche, 1985;Farrell et al, 1998;Jensen et al, 2010). The vertical septum runs from the apex approximately threequarters of the length towards the base of the ventricle, and thereby completely partitions the caudal part of the ventricle into a right and left side.…”

“…Hopkinson and Pancoast, 1837;Jacquart, 1855;White, 1959;White, 1968;White, 1976;Webb et al, 1971;Farrell et al, 1998;Jensen et al, 2010). The heart consists of two separate atria, where the right atrium receives oxygen-poor blood carried by the systemic veins, while the left atrium receives oxygen-rich blood from the lungs.…”