How much do you know about axolotl anatomy? - Part 2, the respiratory system

Have you ever wondered exactly how an axolotl breathes? We all see the gills but is there more to it? How do they work? We're going to jump into all of these questions today by covering axolotl respiration!

What is the main form of axolotl respiration?

It may be a surprise, but the main respiration is not through using their gills! It’s their skin! Like other salamanders, axolotls have thin and moist skin with distal capillaries. These near-the-surface capillaries allow for efficient oxygen diffusion (as well as excretion of carbon dioxide the same way). Their thin skin allows for passive diffusion of gasses through the skin, into the bloodstream, and off to cells that need it for respiration.

What are the other forms of axolotl respiration?

Now we will talk about gills! The gill filaments (also called fimbriae, or affectionately called “floofs”) provide increased surface area for more efficient oxygen uptake from the water. The oxygen is diffused straight into the bloodstream from the gills. The gill rakes are used to keep impurities like parasites from entering the bloodstream. 

FIGURE 6.19. Adaptive types of salamander larvae, or in some cases, paedotypic adults. Adapted from Duellman and Trueb, 1986.

In addition to their skin and gills, axolotls have lungs! These lungs are not very developed, but they are there and function! You may have seen your axolotl swim to the top and take a little gulp of air. This is them using their lungs! They will occasionally come to the top for a breath, which is not abnormal. 

Why is their respiration so different from humans?

Well, axolotls differ pretty significantly from humans, particularly in organs like the heart and lungs. Their lungs are not nearly as developed and efficient, and they don't need to rely on them for oxygen intake like we do. They also have a double circulated, three chamber heart (two atria, one ventricle). This is filled entirely with oxygen rich AND oxygen depleted blood (mixed). They do not prioritize oxygenating blood to high concentrations, but transferring what oxygen they have taken up to the cells that need it. 

Anatomy of the axolotl heart. (A) Ventral view of the in situ axolotl heart showing the principle chambers, namely sinus venosus, atrium (internally divided by an almost complete atrial septum), ventricle and conus arteriosus. The ventricle is positioned on the right and the blunt apex is positioned caudally. The arterial outflow tract is a solitary trunk (truncus arteriosus) with left–right paired channels, giving rise to the third (3rd), fourth (4th), fifth (5th) and sixth (6th) gill arch arteries. There is no diaphragm between the heart and liver. (B) Dorsal view, showing the presence of a left sinus horn. Notice that a solitary pulmonary vein connects to the atrium in a position that equals the human embryonic position, i.e. immediately cranial to the sinus venosus and to the left of the sinuatrial junction. (C) View of the ventricular base and the atrial septum. The pulmonary vein connects to the left atrium in a primitive position, i.e. close to the ventricular base and next to the atrial septum. (D) Left-sided view of the atrial septum, showing a small gap between its leading edge and the atrioventricular canal, i.e. the primary foramen of the atrial septum. (E) Image from microCT showing the highly trabeculated state of the ventricle. Notice there is no ventricular septum, there is a solitary atrioventricular canal (white arrowheads) and a common orifice to the outflow tract (black arrowheads). (F) Ventral-left view of the heart without the atrium (its outline is indicated by the dashed line). Notice the central position of the solitary atrioventricular canal and the cranial-right position of the outflow tract (conus arteriosus). Such topology resembles a double-inlet left ventricle with double-outlet right ventricle. eso, esophagus.

That's the basics! If you have questions, leave them in the comments, shoot our team a message, or ask us how you can join our private Axolotl Help group on Facebook, where we bring all of our combined knowledge and experience together to help solve your axolotl challenges.

And of course stay tuned for our next installment of #NomSafeNovember axolotl anatomy: the digestive system!