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 hormones such as testosterone, which drives male reproductive physiology. Testosterone is important for spermatogenesis, sexual differentiation during embryonic and fetal development, and control of gonadotropin secretion in the pituitary. A metabolite of testosterone, dihydrotestosterone, also begins to act on many tissues during puberty (eg, male accessory glands and hair follicles).
The male reproductive system.
The diagram shows the locations and relationships of the testes, epididymis, glands, and the ductus deferens running from the scrotum to the urethra. The ductus deferens is located along the anterior and superior sides of the bladder as a result of the testes descending into the scrotum from the abdominal cavity during fetal development.
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 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.
Each testis (or testicle) is surrounded by 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 and divide 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) secreting testosterone, and one to four highly convoluted seminiferous tubules in which sperm production occurs.
Testes and seminiferous tubules.
The anatomy of a testis is shown. (a) The diagram shows a partially cutaway sagittal section of the testis. (b) A seminiferous tubule cross section shows spermatogonia (SG) near the periphery, near nuclei of Sertoli cells (SC), primary spermatocytes (PS), and late spermatids (LS) near the lumen, with interstitial cells (IC) in the surrounding connective tissue. (X400; H&E)
Lobules converging at rete testis.
The dense capsule of the testis, the tunica albuginea, thickens on the posterior side as the mediastinum (M) testis, from which many thin septa (S) subdivide the organ into about 250 lobules. Each lobule contains one to four convoluted seminiferous tubules (ST) in a sparse connective tissue interstitium. Each tubule is a loop attached by means of a short straight tubule to the rete testis (RT), a maze ...