Gull and Fin's surf safari yesterday morning:
And now onto other matters: The mammalian diving reflex present in all of us:
As the reflex kicks in, three changes happen to the body, in this order:
1. Bradycardia is the first response to submersion. Immediately upon facial contact with cold water, the human heart rate slows down ten to twenty-five percent.
Seals experience changes that are even more dramatic, going from about 125 beats per minute to as low as 10 on an extended dive.
Slowing the heart rate lessens the need for bloodstream oxygen, leaving more to be used by other organs.
2. Next, peripheral vasoconstriction sets in. When under high pressure induced by deep diving, capillaries in the extremities start closing off, stopping blood circulation to those areas.
Toes and fingers close off first, then hands and feet, and ultimately arms and legs stop allowing blood circulation, leaving more blood for use by the heart and brain.
Human musculature accounts for only 12% of the body's total oxygen storage, and the body's muscles tend to suffer cramping during this phase.
Aquatic mammals have as much as 25 to 30% of their oxygen storage in muscle, and thus they can keep working long after capillary blood supply is stopped.
3. Finally there's the blood shift that occurs only during very deep dives. When this happens, organ and circulatory walls allow plasma/water to pass freely throughout the thoracic cavity, so its pressure stays constant and the organs aren't crushed.
In this stage, the lungs' alveoli fill up with blood plasma, which is reabsorbed when the animal leaves the pressurized environment.
This stage of the diving reflex has been observed in humans (such as world champion freediver Martin Štěpánek) during extremely deep (over 90 metres or 300 ft) freedives.
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