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The Circulatory System


Why does a giraffe have valves in its neck?


The giraffe is the world's tallest animal. Its long neck can get to over 1.5 meters and the average giraffe is 5.5 meters tall. So when a giraffe bends down, wouldn't all the blood in its neck flow straight to its head, resulting in large amounts of pain? Well it would, if it wasn't for valves in their neck. When they bend over, the valves in their neck almost close, which prevents this. They are like the valves in our heart. They act like gates, allowing the oxygenated blood toward the brain, but slowing the blood flow when the giraffe bends over. Because the giraffe is such a tall animal, when it say, bends down to drink, without valves, the blood that would rush to its head could be fatal. If you've ever been upside down for a long period of time, you'll know how this feels. But what if the giraffe had to suddenly lift its head and make a quick getaway. You would expect it to pass out, but again, the valves prevent this.

Human's also have valves that act in a very similar way. We have valves in all the veins in our body to stop the blood from falling and to propel it to the heart. The valves in our neck however aren't as important as a giraffes are because our neck is much shorter in length, meaning the amount of blood that would rush to our head if we were upside down is not nearly as much as a giraffe.


Do spiders have hearts?


Spiders come from the Arachnids class in the athropoda phylum. They are made up of two main body parts, the cephalothorax and the abdomen. The cephalothorax has the eyes, mouthparts and the four legs. The abdomen is connected to the cephalothorax by a narrow pedicel. The entire body is protected by a tough exoskeleton and most parts of the body has sensory hairs growing from the skin. Spiders don't have antennae, instead the sensory hairs pick up scents, sounds, vibrations and air currents.

Spiders have open blood circulatory systems, which has hearts, arteries and veins but no capillaries. The heart is tubular with a single cavity and with valves to maintain the flow of blood always in the same direction. This is essential because when the spider is on a web, this blood will still be able to flow properly. This is very different to the human heart, which has four chambers and is pearshaped. The human body has a closed circulatory system, meaning the blood is confined within vessels.


How many chambers in a fish heart?


Fish hearts are smaller than ours. They only have two chambers in their heart, whereas we have four. They have one atrium and one ventricle. The atrium receives the blood that has been deprived of oxygen. The blood then passes into the ventricle. The ventricle pushed the blood to the gills of the fish where a gas exchange occurs, like in our lungs. The blood then goes to the capillaries, which carry the blood to the rest of the body. Once the blood is deprived of oxygen again, it re-enters the atrium and the process repeats.

This is different to human hearts because we have four chambers, the other two dealing with oxygenated blood. In our hearts, the deoxygenated blood from the right atrium passes into the right ventricle, then gets pushed to the lungs where a gas exchange occurs. The blood then returns to the heart where it enters the left atrium, now as oxygenated blood. It then enters the left ventricle where it is pumped all around the body and into capillaries. After the blood becomes deoxygenated again it returns to the right atrium and the process repeats.


Bibliography EvoWiki 2007, The giraffe neck couldn't evolve without a special circulatory system, 29 October, viewed 10/08/2013, <http://evolutionwiki.org/wiki/The_giraffe_neck_couldn't_evolve_without_ a_special_circulatory_system>. HowStuffWorks 2013, How Spiders Work, viewed 8/08/2013, <http://science.howstuffworks.com/zoology/insectsarachnids/spider1.htm>. Nelson, Nathaniel 2004, What Giraffes will do for a Drink, viewed 9/08/2013, <http://www.apologeticspress.org/apcontent.aspx?category=9&article=13 91>. Nieuwenhuys 2008, The anatomy of a spider, viewed 10/08/2013, <http://ednieuw.home.xs4all.nl/Spiders/Info/spiderinfo.htm>. Unknown 2013, Spider anatomy, 27 March, viewed 9/08/2013, <http://en.wikipedia.org/wiki/Spider_anatomy>. Unknown n.d., The Fish Heart, viewed 9/08/2013, <http://library.thinkquest.org/C003758/Development/fish.htm>. Unknown n.d., The Giraffe, viewed 10/08/2013, <http://www.evolutionfairytale.com/giraffe1.htm>. Unknown n.d., The fish heart - the pump, viewed 10/08/2013, <http://esi.stanford.edu/circulation/circulation5.htm>.


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