well, first off, some thoughts on breathing
my current assignment is to research the mechanisms of how a pleisiosaur holds its breath for such a long time during pre-historic deep sea dives.
well, ive come up with a few thoughts on the subject, and these thoughts have mainly to do with turtles.
now i hear you say a pleisiosaur is not a turtle, that may be the case but consider how similar their body structure and environment is.
they are most definitely related!
leatherback turtles, the deepest diving turtles of the sea, have some ingenious ways of holding their breath.
some basic background:- cells need oxygen and nutrients to survive, grow and regenerate. the nutrients come from the food we eat (in the case of both the pleisiosaur and leatherback, this comes from the fish they eat) and oxygen comes from the air we breathe. here comes the paradox: if cells need a constant supply of oxygen to keep alive, and hence catch the fish, how does one catch fish underwater when there is no air to breathe? and how does one utilise the oxygen from the single breath of air in the lung and keep the cells oxygenated for such a long time?
firstly, its got to do with the lungs (of course)
the deeper you dive, the higher the water pressure is on your body, and hence your lungs. if you cant keep your lungs inflated then they will collapse from the immense pressure of the sea. The leatherback turtle achieves this balance of pressures by pushing the air out of its lungs to non-respiratory parts of their respiratory system (i.e. the parts that arent involved in gas exchange processes) namely the bronchii.
secondly its got to do with the heart.
parallels with hibernation occur here. during a deep dive, the heart rate of a leatherback decreases dramatically, down to around 1 beat per 90 seconds (i could be wrong with the rate/time here, will find out) Now, when your heart rate decreases, so does your rate of breathing. Consider this... if i could somehow slow my heart rate down to 1 beat per 90 seconds, i could stay underwater for 10 minutes on 7 heartbeats. By taking a deep breath and holding it, and taking my pulse, its quite obvious to me that i can hold it for more than 7 beats (just counted 42 beats for 30 seconds)
so if i was to slow my heart rate down to 1 beat per 90 seconds, i would have just been able to hold my breath for 63 minutes. This would be an extremely useful ability to have if you were travelling through say, sydney or many parts of paris.
{now theres something about the heart to do with baroreceptors here (a bunch of nerves around the (?) aorta that detect pressures and adjust the heart rate accordingly) that i will elaborate on a bit later when ive researched its mechanisms a bit more.}
and thirdly, its got to do with your haemoglobin, baby!
leatherbacks have the highest amount of haemoglobin and myoglobin of any reptile. (which means that they have ALOT more than us inefficient humans do) and twice the blood-oxygen carrying capacity of every other turtle. The more oxygen you can carry, the less breathing you have to do, and the more time you can spend in the deep blue chasing fishies.
thats all for now...