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UBC Theses and Dissertations

Functional anatomy and mechanics of the aerodigestive tract in rorqual whales Gil, Kelsey Nicole


Digestive and respiratory pathways are entwined evolutionarily, developmentally, and spatially. Adaptations of the pharynx balance breathing and swallowing, allowing food transfer while maintaining airway protection. Cetaceans have terrestrial ancestry, thus, the terrestrial framework required modifications for life underwater. Rorqual baleen whales have many adaptations related to feeding, which involves engulfing a volume of prey-laden water that can be larger than their own body. How have these adaptations affected interactions of the respiratory and digestive tract? Diving on a breath-hold requires sealing the respiratory tract to prevent water entry; however, this closure presents the risk of barotrauma in the rigid upper airways. Swallowing immense amounts of living food requires protection of upper and lower airways, and requires an effective transport mechanism to swallow large quantities of prey during limited interlunge period. I found that the nasal cavities are protected from water incursion by nasal plugs that occupy the upper half of the nasal cavities. The nasal plugs demonstrate a unique function at depth where they are pushed further into the nasal cavities with increasing ambient ocean pressure and diminishing airway volumes as dive depth increases. The heterogeneous composition of the plugs makes them effective at clearing the upper airways for breathing and filling them when diving to prevent barotrauma. I discovered a novel structure in rorquals, the oral plug, that prevents water incursion into the pharynx during engulfment. Food is prevented from entering the upper airways through elevation of the soft palate and oral plug to close the nasopharynx. Food is prevented from entering the lower airways through occlusion of the laryngeal inlet and collapse of the laryngeal sac into the laryngotracheal junction. With the pharynx dedicated entirely to the digestive tract, food is transported by a pharyngeal pump mechanism, where food is forced through the pharynx by contraction of pharyngeal muscles, into the esophagus and on to the stomach. The actions of dynamic valve mechanisms in the pharynx and larynx allow the pharynx to function efficiently as both part of the respiratory tract and digestive tract in rorqual whales. These adaptations are imperative to achieving large body size in rorquals.

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