Physiology of the Diving Reflex in Humans and Aquatic Aammals and Birds

 

 

What is the Diving Reflex?

The cells of all mammals and birds need oxygen to survive. The source of this oxygen is usually the surrounding air through the process of respiration. However when exhibiting diving behavior, this source of oxygen is lost. Mammals and birds must thus develop strategies to cope with these circumstances. It is upon this basis that the diving reflex, with its corresponding mechanisms and effects, is based upon (Panneton et al., 2010). The diving response enables organisms to preserve oxygen within the blood and thus prolong aerobic metabolism in the two most important organs in the body: the heart and the brain (Ramirez et al., 2007). The cardio-respiratory aspects of the reflex are controlled by the central nervous system, and act as a collective protection mechanism against asphyxia during immersion (Manley, 1990).

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Diving birds: Thick billed murres, emperor penguins, and tufted ducks (images courtesy of Public Domain Images)

There is some discussion over the title of this series of reactions, as the terminology varies between “diving reflex” and “diving response,” yet the two are used synonymously (Gooden, 1994). Although generalized as a single reflex, the diving reflex is actually a complex collection of independent reflexes involving apnea, bradycardia, and peripheral vasoconstriction (Dahms et al., 2010).

What Organisms Use it?

Most diving mammals and birds are endotherms. This gives them an expanded aerobic capacity, but also makes them highly dependent upon an access to oxygen (Ramirez et al., 2007). There is a general trend of greater mass proportional to deeper dives, yet even within this trend there existsa great variety within the diving species (Jones and Butler, 199713). Sperm whales and southern elephant seals can remain submerged for 2 hours at a time, while hooded seals have a maximum dive of 25 minutes (Ramirez et al., 2007). With the exception of the emperor penguin, birds do not dive voluntarily for longer than 1-3 minutes (Butler, 1982).

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Diving mammals: Sperm whale and wendell seal (images courtesy of Public Domain Images)

Humans also utilize the diving reflex, despite some controversy, as the Ama women of Korea and Japan still actively dive for profitable natural products on the sea floor (Gooden, 1994). Much of the diving of any species is determined by the behavior of prey, predators, and physical characteristics of the environment (Jones and Butler, 199713). Despite the marked differences among the species for depth and duration capacity, the pathway of the subsequent diving response remains the same.

 

Why it is important

The diving reflex has been referred to as the “master switch of life,” and the most powerful autonomic response known (Dahms et al., 2010; Panneton et al., 2010, Ross and Steptoe, 1980). Due to its importance within the body, much research as been conducted to determine its presence within a variety of species and to assess its phylogenetic history. It is hypothesized to be an ancient and virtually universal response to conserve oxygen (Manley, 1990). In modern day, it is also essential to certain behaviors such as the alarm response and predation capabilities that directly affect the survival of the organism (Jones and Butler, 1997). Research investigating the diving reflex has been driven for over 100 years by mankind’s desire to uncover the secrets that allows diving organisms to explore a world that is still relatively unknown to humans.

 

 

 

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