What makes them different:
Diving Mammals vs Surface Dwellers
The lungs of diving mammals are collapsible. When they dive and their bodies are under increasing pressure, the lungs in aquatic mammals will be decrease in size and volume. The lungs of a Weddell seal decrease by 15% on a routine dive (1). As show in the figure to the right, the physical structure of the lung is reduced by decreasing the surface area of the bronchiole and alveoli.
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Aquatic Environment vs Terrestial
- The lung capacity, or tidal volume, of marine mammals (like manatees) is much greater than land mammals (2). Land mammals inhale and exhale about 10 to 15 percent of their total lung capacity in one breath (causing tidal volume to be about 75% of total lung volume) . In contrast, marine mammals have a vital capacity that often exceeds 90 percent of their total lung volume (2).
- Marine mammals also have lungs made of more elastic tissue than land mammals, allowing their lungs to fill with more oxygen when at the surface of the water, or compress when diving. In contrast, if a land mammal's lungs collapse it is often deadly (2).
- Like other marine mammals, when diving, a manatee may slow its heart rate to as little as 20% of its normal rate in order to conserve oxygen (1).
- It is a well know fact that marine mammals can hold their breath better than land mammals, but the mechanisms behind the prevention of hypoxia has been somewhat of a mystery. Scientists have determined that mammals in aquatic environments have the ability to greatly decrease their muscle's metabolism during a long under water dive (4). This is done mostly through the use of aerobic cellular respiration, a process that land mammals can survive on for only a few minutes. Another way this is done is by actually decreasing the blood flow to tissues for short periods of time.