Testosterone
<p><b>Testosterone</b> is a <a href="http://en.wikipedia.org/wiki/Steroid_hormone" title="Steroid hormone">steroid hormone</a> from the <a href="http://en.wikipedia.org/wiki/Androgen" title="Androgen">androgen</a> group and is found in mammals, reptiles,<sup id="cite_ref-pmid16326949_1-0" class="reference"><a href="http://en.wikipedia.org/wiki/Testosterone#cite_note-pmid16326949-1">[1]</a></sup> birds,<sup id="cite_ref-pmid16671011_2-0" class="reference"><a href="http://en.wikipedia.org/wiki/Testosterone#cite_note-pmid16671011-2">[2]</a></sup> and other <a href="http://en.wikipedia.org/wiki/Vertebrate" title="Vertebrate">vertebrates</a>. In <a href="http://en.wikipedia.org/wiki/Mammal" title="Mammal">mammals</a>, testosterone is primarily secreted in the <a href="http://en.wikipedia.org/wiki/Testicles" title="Testicles" class="mw-redirect">testicles</a> of <a href="http://en.wikipedia.org/wiki/Male" title="Male">males</a> and the <a href="http://en.wikipedia.org/wiki/Ovaries" title="Ovaries" class="mw-redirect">ovaries</a> of <a href="http://en.wikipedia.org/wiki/Female" title="Female">females</a>, although small amounts are also secreted by the <a href="http://en.wikipedia.org/wiki/Adrenal_gland" title="Adrenal gland">adrenal glands</a>. It is the principal <a href="http://en.wikipedia.org/wiki/Male" title="Male">male</a> sex <a href="http://en.wikipedia.org/wiki/Hormone" title="Hormone">hormone</a> and an <a href="http://en.wikipedia.org/wiki/Anabolic_steroid" title="Anabolic steroid">anabolic steroid</a>.
In men, testosterone plays a key role in the development of male reproductive tissues such as the <a href="http://en.wikipedia.org/wiki/Testis" title="Testis" class="mw-redirect">testis</a> and <a href="http://en.wikipedia.org/wiki/Prostate" title="Prostate">prostate</a> as well as promoting secondary sexual characteristics such as increased <a href="http://en.wikipedia.org/wiki/Muscle" title="Muscle">muscle</a>, <a href="http://en.wikipedia.org/wiki/Bone" title="Bone">bone</a> mass, and the growth of <a href="http://en.wikipedia.org/wiki/Androgenic_hair" title="Androgenic hair">body hair</a>.<sup id="cite_ref-Mooradian__1987_3-0" class="reference"><a href="http://en.wikipedia.org/wiki/Testosterone#cite_note-Mooradian_1987-3">[3]</a></sup>
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In addition, testosterone is essential for health and well-being<sup id="cite_ref-pmid19707253_4-0" class="reference"><a href="http://en.wikipedia.org/wiki/Testosterone#cite_note-pmid19707253-4">[4]</a></sup> as well as the prevention of <a href="http://en.wikipedia.org/wiki/Osteoporosis" title="Osteoporosis">osteoporosis</a>.<sup id="cite_ref-pmid19011293_5-0" class="reference"><a href="http://en.wikipedia.org/wiki/Testosterone#cite_note-pmid19011293-5">[5]</a></sup></p>
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On average, in adult <a href="http://en.wikipedia.org/wiki/Human" title="Human">human</a> males, the plasma concentration of testosterone is about 7–8 times as great as the concentration in adult human females' plasma,<sup id="cite_ref-pmid14981046_6-0" class="reference"><a href="http://en.wikipedia.org/wiki/Testosterone#cite_note-pmid14981046-6">[6]</a></sup> but as the metabolic consumption of testosterone in males is greater, the daily production is about 20 times greater in men.<sup id="cite_ref-pmid6025472_7-0" class="reference"><a href="http://en.wikipedia.org/wiki/Testosterone#cite_note-pmid6025472-7">[7]</a></sup><sup id="cite_ref-pmid5843701_8-0" class="reference"><a href="http://en.wikipedia.org/wiki/Testosterone#cite_note-pmid5843701-8">[8]</a></sup> Females are also more sensitive to the hormone.<sup id="cite_ref-isbn0-07-135739-4_9-0" class="reference"><a href="http://en.wikipedia.org/wiki/Testosterone#cite_note-isbn0-07-135739-4-9">[9]</a></sup> Testosterone is observed in most vertebrates. <a href="http://en.wikipedia.org/wiki/Fish" title="Fish">Fish</a> make a slightly different form called <a href="http://en.wikipedia.org/wiki/11-ketotestosterone" title="11-ketotestosterone" class="mw-redirect">11-ketotestosterone</a>.<sup id="cite_ref-isbn0-87893-617-3_10-0" class="reference"><a href="http://en.wikipedia.org/wiki/Testosterone#cite_note-isbn0-87893-617-3-10">[10]</a></sup> Its counterpart in insects is <a href="http://en.wikipedia.org/wiki/Ecdysone" title="Ecdysone">ecdysone</a>.<sup id="cite_ref-De_Loof_2006_11-0" class="reference"><a href="http://en.wikipedia.org/wiki/Testosterone#cite_note-De_Loof_2006-11">[11]</a></sup> These ubiquitous steroids suggest that <a href="http://en.wikipedia.org/wiki/Sex_hormone" title="Sex hormone" class="mw-redirect">sex hormones</a> have an ancient evolutionary history.<sup id="cite_ref-Mechoulam_1984_12-0" class="reference"><a href="http://en.wikipedia.org/wiki/Testosterone#cite_note-Mechoulam_1984-12">[12]</a></sup></p>