Circulatory System
<p >The <b>circulatory system</b> is an <a href="http://en.wikipedia.org/wiki/Organ(anatomy)" title="Organ (anatomy)" >organ system</a> that passes nutrients (such as <a href="http://en.wikipedia.org/wiki/Amino_acids" title="Amino acids" class="mw-redirect" >amino acids</a>, <a href="http://en.wikipedia.org/wiki/Electrolytes" title="Electrolytes" class="mw-redirect" >electrolytes</a> and <a href="http://en.wikipedia.org/wiki/Lymph" title="Lymph" >lymph</a>), gases, <a href="http://en.wikipedia.org/wiki/Hormone" title="Hormone" >hormones</a>, <a href="http://en.wikipedia.org/wiki/Blood" title="Blood" >blood</a> cells, etc. to and from <a href="http://en.wikipedia.org/wiki/Cells(biology)" title="Cells (biology)" class="mw-redirect" >cells</a> in the body to help fight diseases, stabilize <a href="http://en.wikipedia.org/wiki/Thermoregulation" title="Thermoregulation" >body temperature</a> and <a href="http://en.wikipedia.org/wiki/PH" title="PH" >pH</a>, and to maintain <a href="http://en.wikipedia.org/wiki/Homeostasis" title="Homeostasis" >homeostasis</a>.</p>
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This system may be seen strictly as a blood distribution network, but some consider the circulatory system as composed of the <b>cardiovascular system</b>, which distributes blood,<sup id="cite_ref-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Circulatory_system#cite_note-0" >[1]</a></sup> and the <b><a href="http://en.wikipedia.org/wiki/Lymphatic_system" title="Lymphatic system" >lymphatic system</a></b>,<sup id="cite_ref-1" class="reference" ><a href="http://en.wikipedia.org/wiki/Circulatory_system#cite_note-1" >[2]</a></sup> which returns excess <a href="http://en.wikipedia.org/wiki/Capillary_filtration" title="Capillary filtration" class="mw-redirect" >filtered</a> <a href="http://en.wikipedia.org/wiki/Blood_plasma" title="Blood plasma" >blood plasma</a> from the <a href="http://en.wikipedia.org/wiki/Interstitial_fluid" title="Interstitial fluid" >interstitial fluid</a> (between cells) as <a href="http://en.wikipedia.org/wiki/Lymph" title="Lymph" >lymph</a>. While humans, as well as other<a href="http://en.wikipedia.org/wiki/Vertebrates" title="Vertebrates" class="mw-redirect" >vertebrates</a>, have a closed cardiovascular system (meaning that the blood never leaves the network of <a href="http://en.wikipedia.org/wiki/Arteries" title="Arteries" class="mw-redirect" >arteries</a>, <a href="http://en.wikipedia.org/wiki/Veins" title="Veins" class="mw-redirect" >veins</a> and <a href="http://en.wikipedia.org/wiki/Capillaries" title="Capillaries" class="mw-redirect" >capillaries</a>), some <a href="http://en.wikipedia.org/wiki/Invertebrate" title="Invertebrate" >invertebrate</a> groups have an open cardiovascular system. The most primitive animal <a href="http://en.wikipedia.org/wiki/Phylum" title="Phylum" >phyla</a> lack circulatory systems. The lymphatic system, on the other hand, is an open system providing an accessory route for excess interstitial fluid to get returned to the blood.<sup id="cite_ref-2" class="reference" ><a href="http://en.wikipedia.org/wiki/Circulatory_system#cite_note-2" >[3]</a></sup></p>
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Two types of fluids move through the circulatory system: blood and lymph. Lymph is essentially recycled <a href="http://en.wikipedia.org/wiki/Blood_plasma" title="Blood plasma" >blood plasma</a> after it has been filtered from the <a href="http://en.wikipedia.org/wiki/Blood_cells" title="Blood cells" class="mw-redirect" >blood cells</a> and returned to the lymphatic system. The blood, <a href="http://en.wikipedia.org/wiki/Heart" title="Heart" >heart</a>, and blood vessels form the cardiovascular (from Latin words meaning 'heart'-'vessel') system. The lymph, lymph nodes, and lymph vessels form the <a href="http://en.wikipedia.org/wiki/Lymphatic_system" title="Lymphatic system" >lymphatic system</a>. The cardiovascular system and the lymphatic system collectively make up the circulatory system.</p>