Air-breathing vertebrates

The first air-breathing vertebrates have continued not only to differentiate their chemoreceptor cell types, but also to show some increase in morphological complexity. Amphibia show several adaptive features for fluid intake on land, such as the tentacles of the Caecilians, shown in... 

Surely the science of chemistry will some day reconcile the sense of smell with a reductionist approach in terms of pure compounds. In the interim, this chapter seeks to raise two questions related to the one posed in the opening paragraph what can another organism detect by means of olfaction How might an odor be archived so as to convey it to posterity These questions address the issue of reproducibility of sensation. Unless we take the position that all sensory experiences are unique, some criterion must be advanced to assess whether two stimuli are perceived as similar. Ideally, this criterion should apply to other air-breathing vertebrates as well as ourselves, par-... 

It is true that most of the compounds that normally excite the olfactory organ in fish differ from those to which air breathing vertebrates are exposed, but there is no evidence that the basic transduction mechanisms in air and water differ significantly. It is known, for example, that the same odorants delivered in the aqueous phase, are as effective as when delivered in the vapor phase as judged by the slow voltage shift recorded when a macroelectrode tip was positioned in the nasal cavity of a box turtle during odorant stimulation ( ). 

A further advantage in using fish is anatomical. In air-breathing vertebrates the olfactory chamber extends from the respiratory airway in most fish, however, it is a separate organ divorced from respiratory functions. This feature, and the presence of an aqueous medium, allows us to place a conductivity electrode at the inlet and one at the outlet of the nasal chamber. If electrolytes are used as odorants, their arrival and departure from the chamber can then be measured by conductivity changes. Since conductivity is proportional to concentration we can specify odorant concentration, within known limits, close to the receptors - something which cannot be done with the Intact nasal chamber in air-breathing vertebrates. It is also possible to deliver the odorant in a way that closely imitates that in which it normally arrives ( ). 

The lower vertebrates then possessed a useful nasal device which had already been utilised by their predecessors as a social chemical detector. Air breathing meant that their nasal air-flow was relatively weak in the absence of the pulling power exerted by lungs which... 

Almeida-Val, V.M.F., and P.W. Hochachka (1995). Air-breathing fishes Metabolic biochemistry of the first diving vertebrates. Biochemistry and Molecular Biology of Fishes, Environmental and Ecological Biochemistry 5 45-55. 

Smatresk NJ. Respiratory control in the transition from water to air breathing in vertebrates. Am Zool 1994 34 264—279. 

Mammals are warmblooded vertebrates that have hair and breathe air. All females of this group have milk-producing mammary glands with which to feed their young. Mammals also have a diaphragm that pulls air into the lungs and a four-chambered heart for efficient circulation of blood. The teeth of mammals are specialized by size and shape for particular uses. 

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