Crocs Shunt Blood For Digestion

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Crocs shunt blood for digestion according to an article in ScienceNOW 6 Feb 2008. Crocodiles, alligators and caimans have a four chambered heart similar to that of mammals and birds. In these hearts low-oxygen blood coming back from the body tissues is pumped to the lungs to absorb oxygen and off-load carbon dioxide and then returns to other side of the heart to be sent out the body. Unlike mammals and birds crocodilians can shunt low oxygen blood into the body circulation, bypassing the lungs. This is considered to be a "primitive" function left over from having evolved from amphibians, which have three chambered heart. Scientists at University of Utah, Salt Lake City have investigated the shunting and found that the animals send de-oxygenated to their stomachs after they have eaten. This seemed to confirm a theory that the shunting helped digestion in some way.

The researchers tested the theory by operating on the arteries of some alligators so that they could not shunt the deoxygenated, carbon dioxide rich blood to the stomach. Following this they measured the amount of stomach acid produced when the animals were fed. It was much lower than that of normal animals. The lack of stomach acid meant the animals took longer to digest their food. The scientists were intrigued by the vast amount of acid that normal alligators were able to produce - about 10 times that of most other animals. Being able to rapidly produce large amounts of acid is useful for animals that eat large meals irregularly, and which rely on external sources to get their body temperature up to the level needed for digestive enzymes to work. One of the researchers commented it is the alligators' equivalent of making hay while the sun shines.

Editorial Comment: Crocodilians are considered to be primitive reptiles somewhere between amphibians and mammals, but their circulation is now shown to be not "primitive," and is definitely not slightly better than the 3 chambered amphibians heart, nor an un-evolved leaky version of a mammal's heart. Reptile circulation is just different to fish, frogs and mammals, and if anything more complex than mammals, due to reptiles' highly variable metabolic rates and mechanisms for gaining and circulating heat.

The fact crocs have a four chambered heart does not help the neat progression from a fish to a mammal as shown in evolutionary textbooks, even though the vertebrate heart is often used in the teaching of evolution. Fish only need a two chambered heart because they have low pressure circulation and get oxygen from their gills. Amphibians get some oxygen from their lungs and some from their skin so they do not need complete separation between their lung and body tissue circulation. Mammals and birds need to have a low pressure system for the lungs, and a high pressure system for the body tissues, so they need complete separation of the two systems. The croc differences are now shown to be entirely functionally necessary and so this research confirms the fact each kind of vertebrate has a heart that is appropriate to its needs, and this is good evidence for purposeful creation, not mindless naturalism. (Ref. aorta, haemodynamics, archosaur)

Evidence News 13 February 2008

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