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Liver and Kidney Evolution! Please Help!

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Liver and Kidney Evolution! Please Help!

Postby IheartTiktaalik » Tue Nov 16, 2010 12:36 am

I'm writing several papers for a comparative vertebrate anatomy course, in which, among other things, I will discuss the reasons for anatomical differences in the liver and kidney of various organisms.

I have the class data set for the weights of the liver and kidney of a dogfish shark, mudpuppy (necturus) and cat. (As well as their body weight to do an organ weight vs. body weight analysis)

A shark's liver aids in buoyancy by storing oil, this much is apparent to me. So that guy has a big liver... as for the others.. and kidneys... I am at a loss as to what to say about comparative organ sizes. The only data we have is weight. I'm not sure how this can speak to nephron anatomy if it does at all (for osmoregulation and the like).

Any help is greatly appreciated! Many thanks!
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Re: Liver and Kidney Evolution! Please Help!

Postby BDDVM » Tue Nov 16, 2010 1:42 am

I don't know if this is good or bad for writing your papers but you would be hard pressed to find 3 more disperate animals physiologically. A salt water fish that must excrete salt, a fresh water amphibian that must save salt and eliminate water and an originally desert dwelling carnivour that must save water while eliminating urea. That's just kidneys. Unfortunately organ weight doesn't correlate much with function for kidneys. It's more the microscopic arrangement and length of structures like the loop of Henli that make the difference between a desert cat and an amphibian.
Fish and amphibians also can get some of the kidneys work done through other organs. Electrolyte and ammonia regulation can go through gills/skin which aren't options for the cat.
Don't get caught up in the one trait one adaptation trap. That fat in the sharks liver also stores calories as well as neutralises bouancy.
At least none are herbavours so they have minimal toxin loads in their diets (less work for the liver).
Evolution is all about the niche. If you start talking about things that don't refer back to the niche you're probably blowing smoke.
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Postby IheartTiktaalik » Tue Nov 16, 2010 3:27 am

Yes, the ever-important environment is a major player in my explanation of function. Sharks are isotonic to their environment, so I suppose their kidneys don't work too hard to excrete salts and save water... But still I agree.. I'm not sure how weight will speak to nephron anatomy. Arg!

I did think, however, that the fact that these animals were so different would be a good thing. I figured their anatomy would dramatically reflect their different environments... but as I start my data analysis there is NO significant difference in kidney percent of body weight (p-value HUGE) however there IS a statistically significant difference in the percent of body weight that the liver takes up in Sharks v. Mudpuppy. Sharks obviously having a liver that has a larger % of the body weight than mudpuppies.

You still gave me some info I hadn't thought of... ammonia regulation with gills etc... cats cant do that.. etc. When I get the cat kidney data there might be something there... cause there sure isn't a difference between the shark and the mudpuppy!

Thank you so much for sharing!

:)
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