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Normal testicular function is necessary for external genital development and function, diverse psychosexual dimorphic features, normal muscle, and bone structure*. Depending on age and developmental stage, underlying defects may have variable phenotypic presentations. For example, deletion of the AZF region of the Y chromosome will result in spermatogenic failure during puberty and in adulthood, but has no effect on normal childhood development and timing or progression of puberty. Most defects in Leydig cell, Sertoli cell, or germ cell function may have subtle but variable presentation from fetal period to adolescence. Thus, it is helpful to consider hypogonadism as disorder of specific cell populations like Leydig cells, germ cells, or Sertoli cells, remembering that close and tight interactions between Sertoli and germ cells exist and are critical in normal testicular function1 (Table 38-1). A broader definition of hypogonadism, applicable to males from fetal life to adulthood, requires a comprehensive consideration of the physiology of the hypothalamo-pituitary-testicular axis and its disturbances along development. In this chapter, we address male hypogonadism based on the pathophysiology of the hypothalamo-pituitary-testicular axis in different periods of life.
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ANATOMY, EMBRYOLOGY, AND DEVELOPMENT
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The Hypothalamic-Pituitary Axis
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The pituitary is a hormonally active gland in the midline, at the base of the brain, within the bony sella turcica and covered by the diaphragma sella, a reflection of the dura mater. Cavernous sinuses are lateral, the sphenoid sinus and the optic chiasm anterior, and ...