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Toothy valves control crocodile hearts.



Inside their hearts, crocodiles have toothlike gear cogs. Researchers now have figured out what makes those teeth clench.

Unlike more standard heart valves Heart valves
Valves that regulate blood flow into and out of the heart chambers.

Mentioned in: Heart Failure
, which swing open or closed as blood pressure changes, the cogs interlock A device that prohibits an action from taking place.  to reroute blood in response to changing hormone levels, say Craig E. Franklin of the University of Queensland The University of Queensland (UQ) is the longest-established university in the state of Queensland, Australia, a member of Australia's Group of Eight, and the Sandstone Universities. It is also a founding member of the international Universitas 21 organisation.  in Australia and Michael Axelsson of the University of Goteborg in Sweden. "To our knowledge, this is the first report of an actively controlled intra-cardiac vane Vane , John Robert 1927-2004.

British pharmacologist. He shared a 1982 Nobel Prize for research on prostaglandins.



vane

the membranous or main part of the contour feather in birds as distinct from the shaft.
 in a vertebrate," they claim in the Aug. 24 NATURE.

"What we've shown here is an evolutionary novelty," Franklin says. "The crocodile heart is the most complex and the most bizarre in terms of its plumbing."

Crocodilians--alligators, crocodiles, caimans, and gavials--run on four-chambered hearts, as do mammals and birds. Other reptiles power their circulatory systems with three-chambered hearts.

Most vertebrates control cardiac blood flow with what Franklin calls passive valves. Thin leaves of tissue simply flap open when pressed by surging blood and then snap shut when the surge subsides. In contrast, an active valve like the one he proposes for crocodiles works more like automatic doors triggered by a motion sensor to slide open.

Since the 19th century, biologists have known that crocodilians have cogged teeth made of connective tissue. They're located just inside the valve flap of the right ventricle. To figure out what controls the valve, Franklin and Axelsson monitored its activity in a beating heart from an estuarine es·tu·a·rine  
adj.
1. Of, relating to, or found in an estuary.

2. Geology Formed or deposited in an estuary.

Adj. 1. estuarine - of or relating to or found in estuaries
estuarial
 crocodile, Crocodylus porosus. They treated the heart with sotalol, a compound that blocks one of the receptors for fight-or-flight hormones. This blockage of the beta-adrenoceptor mimics the low-adrenaline state of a relaxed croc.

Under these circumstances, the cogs interlocked, shunting blood that had just come from the body back for another tour instead of sending it to the lungs to reload (1) To load a program from disk into memory once again in order to run it. Reload is entirely different than reinstall. Reinstall means that you have to run the install program from a CD-ROM or floppy disk and perform the installation procedure over again.  oxygen.

The researchers next reversed the relaxation effect by administering adrenaline and related compounds that overwhelmed sotalol's binding to the receptor. The cogs responded by opening and permitting blood to flow to the lungs.

That finding contradicts long-held assumptions, explains James W. Hicks, who studies reptile cardiology at the University of California The University of California has a combined student body of more than 191,000 students, over 1,340,000 living alumni, and a combined systemwide and campus endowment of just over $7.3 billion (8th largest in the United States). , Irvine. Since the 1960s, biologists have known that crocs Crocs Inc. (NASDAQ: CROX) is an American company founded by Lyndon "Duke" Hanson, Scott Seamans, and George Boedecker[1] in July 2002. Based in Boulder, Colorado, the firm was created to market a lightweight plastic shoe first developed and manufactured by Foam , turtles, and some other creatures can shunt the blood away from the lungs. However, experiments had suggested that passive mechanisms outside the heart are at work. In turtles, for example, when lung blood vessels constrict con·strict
v.
To make smaller or narrower, especially by binding or squeezing.
, blood taking a path of less resistance washes back to the body.

In the new work on crocodiles' valves, "it's the active component within the heart that, to me, makes it exciting," Hicks says.

There's still no solid explanation of why certain animals shunt their blood in the first place, Hicks observes. One conjecture is that the tactic might somehow enable diving animals to stretch their oxygen supply, but mathematical models cast doubt on whether the divers would get very much benefit. Hicks finds that surgery to prevent alligators from shunting blood makes no difference in their first-year growth.

Says Hicks: "What we really need to do is find when shunting occurs in the wild."
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Author:Milius, S.
Publication:Science News
Article Type:Brief Article
Date:Aug 26, 2000
Words:513
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