An investigation of the presence of a caval sphincter in the diaphragm of dwarf sperm whales (Kogia simus)
Andrea Glaser and Jennifer L. Dearolf, Biology Department, Hendrix College, Conway, AR
Cetaceans (whales, dolphins, and porpoises) are marine mammals capable of high speed swimming and very deep dives. As cetaceans dive into deep waters, the amount of pressure within their body cavities increases due to the water pressure at great depths. To date, there have been no studies to determine if a caval sphincter, a structure found in deep diving pinnipeds (seals, sea lions, and walruses) that controls blood flow back to the heart during dives of depth, is present in cetaceans. However, there is a funnel shaped sling of muscle surrounding the vena cava in these animals. We hypothesize that the sling of striated muscle found in dwarf sperm whales (Kogia simus) does function as a postcaval sphincter and therefore, should have a higher percentage of slow-twitch (type I) fibers in comparison to the costal diaphragm. To test this hypothesis, histochemical and biochemical techniques were used to compare the fiber-type profiles of the costal diaphragm and caval sling in Kogia. We found that there is an increased percentage of type I fibers in the caval sling region (46.6% vs 42.0%). In addition, we saw a significant difference between the two Kogia specimens in the diameters of type I fibers (34.61µm vs 53.71µm). We also collected interesting metabolic staining data for both type I and type II (fast-twitch) fibers that are suggestive of a region-specific metabolic profile for both fiber types. Thus, we conclude that the caval sling in Kogia simus could have a sphincter-like function, but we suggest that more detailed study of the region is required.
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