Gastrointestinal Tract
<p >The <b>human gastrointestinal tract</b> is the <a href="http://en.wikipedia.org/wiki/Stomach" title="Stomach" >stomach</a> and <a href="http://en.wikipedia.org/wiki/Intestine" title="Intestine" >intestine</a>,<sup id="cite_ref-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Gastrointestinal_tract#cite_note-0" >[1]</a></sup> sometimes including all the structures from the <a href="http://en.wikipedia.org/wiki/Human_mouth" title="Human mouth" class="mw-redirect" >mouth</a> to the <a href="http://en.wikipedia.org/wiki/Anus" title="Anus" >anus</a>.<sup id="cite_ref-1" class="reference" ><a href="http://en.wikipedia.org/wiki/Gastrointestinal_tract#cite_note-1" >[2]</a></sup> </p>
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(The "digestive system" is a broader term that includes other structures, including the <a href="http://en.wikipedia.org/wiki/Accessory_organs_of_digestion" title="Accessory organs of digestion" class="mw-redirect" >accessory organs of digestion</a>).<sup id="cite_ref-2" class="reference" ><a href="http://en.wikipedia.org/wiki/Gastrointestinal_tract#cite_note-2" >[3]</a></sup></p>
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In an <a href="http://en.wikipedia.org/wiki/Adult" title="Adult" >adult</a> <a href="http://en.wikipedia.org/wiki/Male" title="Male" >male</a> <a href="http://en.wikipedia.org/wiki/Human" title="Human" >human</a>, the gastrointestinal (GI) tract is 5 metres (20 ft) long in a live subject, or up to 9 metres (30 ft) without the effect
of <a href="http://en.wikipedia.org/wiki/Muscle_tone" title="Muscle tone" >muscle tone</a>, and consists of the upper and lower GI tracts. The tract may also be divided into <a href="http://en.wikipedia.org/wiki/Foregut" title="Foregut" >foregut</a>, <a href="http://en.wikipedia.org/wiki/Midgut" title="Midgut" >midgut</a>, and<a href="http://en.wikipedia.org/wiki/Hindgut" title="Hindgut" >hindgut</a>, reflecting the <a href="http://en.wikipedia.org/wiki/Embryology" title="Embryology" >embryological</a> origin of each segment of the tract.</p>
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The GI tract always releases <a href="http://en.wikipedia.org/wiki/Hormone" title="Hormone" >hormones</a> to help regulate the digestion process. </p>
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These hormones, including <a href="http://en.wikipedia.org/wiki/Gastrin" title="Gastrin" >gastrin</a>, <a href="http://en.wikipedia.org/wiki/Secretin" title="Secretin" >secretin</a>, <a href="http://en.wikipedia.org/wiki/Cholecystokinin" title="Cholecystokinin" >cholecystokinin</a>, and <a href="http://en.wikipedia.org/wiki/Grehlin" title="Grehlin" class="mw-redirect" >grehlin</a>, are mediated through either <a href="http://en.wikipedia.org/wiki/Intracrine" title="Intracrine" >intracrine</a> or <a href="http://en.wikipedia.org/wiki/Autocrine" title="Autocrine" class="mw-redirect" >autocrine</a> mechanisms, indicating that the cells releasing these hormones are conserved structures throughout <a href="http://en.wikipedia.org/wiki/Evolution" title="Evolution" >evolution</a>.<sup id="cite_ref-3" class="reference" ><a href="http://en.wikipedia.org/wiki/Gastrointestinal_tract#cite_note-3" >[4]</a></sup></p>