Sharks are AWESOME part 2!!

Greetings everyone,
Carrying on with the theme of enhancing your knowledge on shark biology we bring to you answers to some pretty puzzling shark questions. Starting with...

On the 19th of July 2013 a Mako shark (seen below) was spotted in British waters for the first time in 42 years and in 2012 a great white was spotted 12 miles from Cornwall, how are they able to enter such cold water when sharks usually occupy warmer waters?

Well lets start of by saying that most bony fish (except for tuna) and most sharks are considered to be ectothermic meaning they are unable to warm themselves through their metabolism,  this is the reason why many sharks have to remain in warmer waters. However, the exceptions to this rule are the mackeral sharks, these include your Mako sharks and your Great White Sharks and the common Thresher shark, all of these sharks are considered to be endothermic. But why?
They owe this adaptation to a network of blood capillaries called the rete mirabile, with blood flowing in opposite directions that are able to act as a heat exchanger. In simple terms, heat is transferred to the blood that is flowing back into the body from the gills, whilst the blood that is flowing out now looses less heat to the surroundings. This remarkable adaptation allows for the temperature inside the body to be 5-14 degrees above the temperature of the surrounding water!!
There are three retia areas that are known. 
  1. Swimming muscles
  2. Brain
  3. The intestines in particular the stomach

A sharks skeleton is made out of only cartilage, so if they lack bone marrow how does a shark make red blood cells?

This posed as a huge mystery to all scientists when they realized that a sharks skeleton is made out of cartilage, that was till they found that this job was performed by the spleen. In case it has slipped your mind what a mammals spleen does, a mammals spleen filters out old red blood cells, whereas the spleen in most sharks generates red blood cells. It is found near the reproductive organs. However not all sharks share this red blood cell generator, some species have a special structure called the Leydigs organ, in the species that this occurs in is is usually nestles along the top and bottom of the esophagus. 

Is it true that sharks live cancer free?

No. Sharks are not a cancer free species, they are just very, very unlikely to have a tumor. It was found that of the large quantity of fish tumors held at the Smithsonian only 15 are from elasmobranchs (sharks and rays), and of which only two were malignant. 
Tumors is basically an uncontrolled cellular growth, and in order to support their very high metabolisms they secrete a hormone called angiogenin. Angiogenin causes nearby blood vessels to grow new branches surrounding the tumor thereby securing a transport system that bring by all the nutrient they need and removes all they waste as well. 
Now, sharks are unlikely  to have tumors because they naturally produce a compound that has antagonistic effects of angiogenin. It was conveniently named angiogenin inhibitor, and does just what it says in the title, it inhibits in other words stops the tumor from gaining a nutrient supply, and with no waste removal the tumor begins to 'choke' on its own waste.

Well this marks the end of Shark Week for us here on Biobunch we hope that you gained some new insights into shark behaviour anatomy and physiology, until next time guys this is...
over and out.

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