User:Grayzacc/Plethodontidae

Respiration[edit]
A number of features distinguish the plethodontids from other salamanders. Most significantly, they lack lungs, conducting respiration through their skin, and the tissues lining their mouths. Some species of cave salamanders are neotenic, and keep their larval gills even as adults. Gills are absent in all other adult plethodontids.

'''Plethodontid salamanders are almost entirely reliant on cutaneous respiration. They are constantly exposed to air or water, which allows for constant gas exchange that is not limited by ventilation. Oxygen uptake is identical in water and air, assuming the partial pressure of oxygen is the same. Oxygenated and non-oxygenated blood are mixed together in the venous system, which causes the partial pressure of oxygen within cardiac blood to typically be low. Plethodontids can tolerate hypoxia for prolonged periods by reducing their metabolic rate. '''

'''Plethodontids have been observed to develop rudimentary lungs as embryos. The lung rudiment develops similarly to that of non-plethodontid salamanders for the first three weeks of development and then begins to regress through apoptosis.'''