Weddle Seal
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Even though both Weddell seals and humans breathe oxygen to stay alive their bodies are different physiologically. Weddell seal bodies differ from human bodies in that they are able to hold much more oxygen in their blood and their muscles than human bodies. This allows the seals to hold their breath for more than seventy-five minutes whereas humans have to come up to the surface after only five minutes. The red blood cells within the blood contain a protein called haemoglobin. This pigment, which is found in all vertebrates, contains iron, and this is responsible for the binding of oxygen. The more haemoglobin you have, the more oxygen in the blood; therefore fewer inhaled breaths. If the oxygen level in the blood falls, a hormone produced by the liver and kidneys stimulates the bone marrow to produce more red blood cells.
Another reason seals can dive for longer is that they can release stored red blood cells into their circulation from a storage compartment in the spleen. This will, in addition to immediately increasing the available oxygen stores, facilitate the uptake of oxygen and release of carbon dioxide during brief surface intervals between dives. The signal for the spleen to empty its cells into the circulation is the hormone epinephrine. The extra blood with its haemoglobin allows a seal about fifteen extra minutes underwater.
Furthermore the Weddell seal has a high concentration of an oxygen storing protein called myoglobin in their muscles compared to humans. Once the oxygen in the blood has depleted, the oxygen bound to myoglobin begins to come off and enter the cytoplasm of the muscles cells.
Myoglobin helps seals deal with the increased amounts of carbon dioxide in its bloodstream. Muscles receive virtually no blood during a dive. After the small amount of oxygen in the muscles is used up, the work of the muscles is based on anaerobic respiration, which leads to the formation of lactic acid in the muscles. Seals are capable