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- Describe the physiologic functions of the principal components of the male reproductive system.
- Describe the endocrine regulation of testicular function by gonadotropin-releasing hormone, follicle-stimulating hormone, luteinizing hormone, testosterone, and inhibin.
- Identify the cell of origin for testosterone, its biosynthesis, mechanism of transport within the blood, metabolism, and clearance. List other physiologically produced androgens.
- List the target organs or cell types, the cellular mechanisms of action, and the physiologic effects of testosterone.
- Describe spermatogenesis and the role of different cell types in this process.
- Understand the neural, vascular, and endocrine factors involved in the erection and ejaculation response.
- Compare and contrast the actions of testosterone, dihydrotestosterone, estradiol, and müllerian inhibitory factor in the process of sexual differentiation.
- Identify the causes and consequences of androgen oversecretion and undersecretion in prepubertal and postpubescent adult males.
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In utero sexual differentiation, maturation, spermatogenesis, and ultimately reproduction are all functions of the male reproductive system that are under endocrine regulation. The 2 principal functions of the testicles, the adult male sex organs, are the production of sperm and the synthesis of testosterone. These processes ensure fertility and maintain male sexual characteristics, or virility. Testicular function is under central nervous system control in a classic neuroendocrine feedback loop with the gonadotropins follicle-stimulating hormone (FSH) and luteinizing hormone (LH) as the key hormonal signals. These gonadotropins, as discussed in Chapter 2, are under the influence of hypothalamic gonadotropin-releasing hormone (GnRH) stimulation. Additional paracrine, neural, and endocrine factors contribute to the complex regulation of the hypothalamic-pituitary-gonadal axis. This chapter discusses the basic principles of endocrine regulation of the male reproductive system.
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The male reproductive organs include the testes (the central male sex organs), the vas deferens, the ejaculatory ducts, the penis, and the accessory glands, which include the prostate and bulbourethral glands (Figure 8–1). The testes consist of numerous lobules made of convoluted tubes (tubuli seminiferi) supported by loose connective tissue. The seminiferous tubules represent approximately 80%–85% of the testicular mass or volume. The tubules consist of a basement layer lined with epithelial (Sertoli) cells forming the walls of the seminiferous tubules. These tubules are lined with primitive germ cells (spermatogonia). The Leydig cells are embedded in the connective tissue are the endocrine cells responsible for the production of the most important circulating androgen, testosterone.
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