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<p>Hormones are chemical messengers produced by glands in the <em><a href="/dictionary/endocrine_system">endocrine system</a></em>. Endocrine tissues are specialised to produce such hormones, which have genes switched on according the the hormones they were designed to produce. The <a href="/1/6_protein_synthesis.htm">protein synthesis</a> pages in the cell biology tutorial go into depth about protein production, which is relevant here as hormones consist of <em><a href="/dictionary/protein">proteins</a></em>.</p> <p>The pituitary gland situated at the back of the brain is responsible for the creation of many hormones that are related to growth in animals. The amount of each hormone produce is regulated by the <em><a href="/dictionary/hypothalamus">hypothalamus</a></em>, a part of the brain situated next to the <em><a href="/dictionary/pituitary_gland">pituitary gland</a></em>.</p> <h2>Hypothalamus and the Pituitary Gland</h2> <p>As stated, the hypothalamus is responsible for regulating the release of hormones from the pituitary gland. It is responsible for secreting <em><a href="/dictionary/releasing_factors">releaser factors</a></em> which instruct the pituitary gland to secret certain hormones. This is illustrated below.</p> <p><img alt="Hormone target tissue example" src="/images/hormone_target.gif"></p> <ul><li>In Figure 1 above, the releaser hormone from the hypothalamus finds its target tissue, a pituitary cell. It binds to the receptor where a chemical messenger instructs the cell to release the desired hormone. </li> <li>In figure 2, the messenger may instruct the release of the hormone, or bind to the receptor and enter the nucleus to instruct the production of a particular hormone </li> <li>Finally, the secreted hormone will target a specific tissue (for instance the thyroid gland) and instruct the tissue to produce a particular substance </li> </ul><h2>Hormone Use</h2> <p>Essentially, the Jacob-Monod hypothesis explained in the genetic control page of this tutorial is the model that is involved in the production of hormones</p> <ul><li>Demands for certain substances vary in an organisms daily function and lifecycle. For instance adolescence in humans requires the production of gonadotrophic hormones, hormones that target the sex organs at that time of maturing in the body </li> <li>The demand is realised and genes are switched on to code for the induction and secretion of hormones involved in growth of the organism </li> <li>Hormones are secreted in their target tissues and their chemical messages understood </li> <li>Desired effects of hormones take place, such as the ability to produce functional gametes for reproduction, growth and development of a deeper voice and body hair </li> </ul><p>Essentially hormones are used on demand by the body to instruct cells in particular tissues to devote their resources to the production of a particular protein</p> <p>The next page investigates the use of these hormones in animals with successive pages studying plant hormones.</p>
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