The anterior and preoptic hypothalamic areas are sites for regulating gonadotropic hormone secretion and sexual behavior. Neurons in the preoptic area secrete gonadotropin-releasing hormone (GnRH), beginning at puberty, in response to signals that are not understood. These neurons contain receptors for gonadal steroid hormones, testosterone and/or estradiol, which regulate GnRH secretion in either a cyclic (female) or a continual (male) pattern following the onset of puberty.
At a critical period in fetal development, circulating testosterone secreted by the testes of a male fetus changes the characteristics of cells in the preoptic area that are destined later in life to secrete GnRH. These cells, which would secrete GnRH cyclically at puberty, had they not been exposed to androgens prenatally, are transformed into cells that secrete GnRH continually at a homeostatically regulated level. As a result, males exhibit a steady-state secretion rate for gonadotropic hormones and, consequently, for testosterone (see Chapter 37).
In the absence of androgens in fetal blood during development, the preoptic area remains unchanged, so that at puberty the GnRH-secreting cells begin to secrete in a
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.