Various marine mammals have been found to have adapted special abilities which help in their respiratory processes, enabling them to remain down at great depths for long periods of time. The Weddell seal posseses some amazing abilities. It only stores 5% of its oxygen in its lungs, and keeps the remaining 70% of its oxygen circulating throughout the blood stream. Humans are only able to keep a small 51% of their oxygen circulating throughout the blood stream, while 36% of the oxygen is stored in the lungs. The explanation for this is that the Weddell seal has approximately twice the volume of blood per kilogram as humans. As well, the Weddell seal's spleen has the ability to store up to 24L of blood. It is believed that when the seal dives the spleen contracts causing the stored oxygen enriched blood to enter the blood stream. Also, these seals have a higher concentration of a certain protein found within the muscles known as myoglobin, which stores oxygen. The Weddell seal contains 25% of its oxygen in the muscles, while humans only keep about 12% of their oxygen within the muscles.
Not only does the Weddell seal store oxygen for long dives, but they consume it wisely as well. A diving reflex slows the pulse, and an overall reduction in oxygen consumption occurs due to this reduced heart rate. Regulatory mechamisms reroute blood to where it is needed most (brain, spinal cord, eyes, adrenal galnds, and in some cases placenta) by constricting blood flow where it is not needed (mainly in the digestive system). Blood flow is restricted to mucles during long dives and they rely on oxygen stored in their myoglobin and make their ATP from fermentation rather then from respiration.
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