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The male reproductive system consists of the testes, genital ducts, accessory glands, and penis (Figure 21–1). Testes produce sperm but also contain endocrine cells secreting testosterone, which drives many aspects of male reproductive physiology. Testosterone influences sexual differentiation during embryonic and fetal development, activates spermatogenesis, and controls gonadotropin secretion in the pituitary. A metabolite of testosterone, dihydrotestosterone, also begins to act on many tissues during puberty, including the male accessory glands and hair follicles.
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The genital ducts and accessory glands produce secretions required for sperm activity and contract to propel spermatozoa and the secretions from the penile urethra. These secretions also provide nutrients for spermatozoa while they are confined to the male reproductive tract. Spermatozoa and the secretions of the accessory glands make up the semen (L. seed), which is introduced into the female reproductive tract by the penis.
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Each testis (or testicle) has a dense connective tissue capsule, the tunica albuginea, which thickens on the posterior side to form the mediastinum testis. From this fibrous region, septa penetrate the organ, dividing it into about 250 pyramidal compartments or testicular lobules (Figures 21–2 and 21–3). Each lobule contains sparse connective tissue with endocrine interstitial cells (or Leydig cells) for testosterone synthesis, and one to four highly convoluted seminiferous tubules in which sperm production occurs.
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