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Species: Ambystoma mexicanum

DECRIPTION

Axolotls can regenerate, repair or replace its arms, legs, tail, lower jaw, brain and heart.

This species is a popular model organism in the field of regenerative medicine, due to its ability to regenerate for instance functional heart muscle after injury.

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Species: Plethodon cinereus

DECRIPTION

Species under lungless plethodontid salamanders (Plethodontidae).

Plethodontid salamanders have partial
atrial septa and incomplete separation of the atrium into left and right halves.

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Species: Onychodactylus japonicus

DECRIPTION

Belongs to convergently lungless species.

Characterized by partial septation.

Atrial morphology of the convergently lungless salamander Onychodactylus japonicus is similar to that of plethodontids and evolved independently.

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➖ Atrial Septum Reduction in Lungless Salamanders


Within an approximate number of 700 species of living salamanders, it has been said that nearly two thirds are lungless. Since then, this resulted to contradictory hypotheses regarding the atrial septum morphology of these lungless salamanders. The results of the study showed that lung loss dramatically impacted the configuration of the circulatory system and the effects of evolutionary lung loss on cardiac morphology, particularly, in atrial septum reduction in lungless salamanders. With this, we can infer that the morphology of lungless salamanders represents an evolutionary loss of a prominent
portion of the atrial septum.

"Although some species of plethodontids retain the pulmonary arch, adult lungless amphibians lack pulmonary veins. Consequently, all blood ﬂowing into the heart originates from the left and right common cardinal veins and the posterior cardinal vein via sinus venosus. Since this blood is from a single mixed source, lungless amphibians do not require separation of blood in the heart. In fact, the presence of an atrial septum might be disadvantageous in this situation, which could lead to extreme pressure differentials between atrial chambers."

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➖ Heart Regeneration

At any life stage, salamanders have the ability to regenerate its functional heart muscle after an injury. A study finds that cardiac regeneration of these species relies on  the presence of macrophages, a type of white blood cell. However, as counter-intuitive as it may seem, alterations in leukocyte numbers does not affect regeneration, structurally and functionally.

"Macrophage populations are largely restored in axolotls, at which point any pro-angiogenic functions are likely impacted by rigid fibrotic ECM associated with early macrophage depletion. New blood vessel growth is likely to impact the speed of regeneration in axolotls however the thin trabeculated (non-compacted) structure of the myocardium likely allows some access of oxygenated blood to the injured tissue. Therefore is is possible that angiogenesis may not be an absolute requirement for allowing the regeneration of an amphibian heart."

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DESCRIPTION

In modern amphibians (frogs, toads, salamanders) the atrium is completely separated by a partition into two atria. The right atrium receives venous blood from the body while the left atrium receives oxygenated blood from the lungs. The ventricle is undivided, but venous and arterial blood remain mostly separate by the arrangement of vessels leaving the heart.

The heart muscle of salamanders are so thoroughly channeled with spaces between muscle fibers that the heart’s own pumping action squeezes through sufficient oxygenated blood.

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NAME: Raina temporaria
DECRIPTION:
➖ three-chambered heart
➖ smooth skinned but varies in color

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NAME: Conraua goliath
DECRIPTION:
➖ triangular head and robust limbs
➖ three-chambered heart

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NAME: Lithobates pipiens
DECRIPTION:
➖ array of irregularly shaped dark spots
➖ three-chambered heart

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NAME: Xenopus laevis
DECRIPTION:
➖ body is flattened
➖ head is wedge-shaped
➖ usually used as a model system for vertebrate heart development

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➖ Cardiac Development: Morphogenetic Study of Heart Tube Formation

A study shows that the heart tube, which up to this time has remained one
cell deep, thickens and the inner portion gives rise to the myocardium, while the outer layer forms the thin visceral portion of the pericardium. The heart tube becomes disconnected entirely from the parietal layer of pericardium, so that no ventral mesocardium persists and the pericar-
dium continuously lines the pericardial space. Anteriorly in the tadpole, the truncus ateriosus divides into two branches that continue to the aortic arches and connect to the gill filaments.

“Two centuries of amphibian cardiogenesis research have been instrumental in providing a coherent picture of how signaling pathways specify and form vertebrate heart tissue during early embryonic development. The past decade
in particular has been remarkable because of the advance made in uncovering the nature of embryonic signals.”

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➖ Heart : Two atria instead of one

A study on the investigation of a vertebrate’s heart chamber shows that frogs evolved to have two atria instead of one but still only have one ventricle.

“Five hundred and fifty million years ago the hearts of the entire animal world were simple tubular hearts, something that still characterizes heart development at the early embryonic stages in animals today. However, as time went by in certain lineages the hearts became increasingly sophisticated. As they became more sophisticated, new switches for the add-ons were put into place.”

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DESCRIPTION

This figure above shows the circulatory system of frogs. This evolutionary analysis will focus on the frog’s heart and cardiac development.