whale hearts -- 6/30/21

Today's selection -- from Spying on Whales: The Past, Present, and Future of Earth's Most Awesome Creatures by Nick Pyenson. Whale hearts are so large a person could fit inside one:
 
"Whale hearts are built like all mammalian hearts -- four cham­bers, split into a right and left set, with smaller atria and larger ventricles -- but they dwarf all others in size. Imagine, for the largest of whales, a heart the size of a farm tractor tire. Your whole body could fit inside one of these organs.

"Whales also rank on the high end of mammals in terms of blood volume to body size, and that volume is astounding, amounting to thousands of liters of blood. In any mammal, the muscle walls of the heart need to push that blood volume throughout the entire circulation system of the body -- and send it all the way back to the heart on the return. Consequently, the blood pressure in the aorta (the first main pipe off the heart) is the greatest of any place in the whole circulation system. This pressure wave, however, drops off abruptly as the beat ends and then restarts with every cycle of the heart pumping.

"The aorta has to be flexible enough to accommodate the sud­den and repeated changes in pressure without blowing out. As mammals increase in size, both the thickness of the aorta walls and the aorta's diameter increase; the ratio of wall thickness to diameter holds steady across all mammals from mice to ele­phants, and whales follow this pattern too. In most mammals, the aortic arch has elastic properties thanks to a protein called elastin. What Bob [Shadwick] and his colleagues discovered, however, was that there's more than just elastin in the aortas of gigantic whales: there is also a unique lattice of collagen sheets that pro­vide extra, microscopic anatomical flexibility for the aorta to successfully withstand blood pressure straight from the heart."


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author:

Nick Pyenson

title:

Spying on Whales: The Past, Present, and Future of Earth's Most Awesome Creatures

publisher:

Penguin Books

date:

Copyright 2018 by Smithsonian Institution

pages:

144-145
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