ISSN:
1432-234X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary Heat stressed pigeons dissipate heat by panting and gular flutter which is associated with upper esophageal pulsation; these activities depend on evaporative cooling and convection from mucosal surfaces. The collar plexus, an unusual subcutaneous system of erectile veins, is the specialized vascular apparatus that seems to serve as the heat exchanger for gular flutter and upper esophageal pulsation. The collar plexus lies between the dermis and a deeper muscle sheet, extending from the head to the thoracic inlet in mature pigeons. The slightly filled plexus is inconspicuous, resembling an ordinary venous bed, and consists of thick-walled veins having small lumina, similar to arteries. When moderately-filled, the veins of the plexus distend and abruptly transform into “beaded” veins with contorted, sacculated expansions separated by constricted segments. During heat stress, engorgement of the plexus occurs rapidly by continual flow over arteriovenous anastomoses that empty arterial blood directly into the beaded veins. Constriction of veins draining the plexus impedes venous return to the jugular veins, thereby maintaining tumescence of the plexus. Disgorgement of the plexus also occurs abruptly. Intimate contact between the deep aspect of the engorged plexus and the trachea and upper esophagus provides for heat transfer from the plexus to the mucosal surfaces of these structures where evaporative cooling takes place. During esophageal pulsation the esophageal surface extends and augments the respiratory dead-space area used for evaporative cooling. Thus a possible advantage of cooling by upper esophageal pulsation is that, like gular flutter of the oropharynx, it may minimize the amount of air that must pass over gas exchange surfaces, thereby limiting the washout of CO2 and consequent acid-base disturbances that occur during panting in extreme heat stress. Ability to inflate the esophagus is of general occurrence among the pigeons and doves (Family Columbidae). The collar plexus is also widespread, having been found in representatives of five of the examined six main subdivisions of the Columbidae.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00310349
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