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The Male Reproductive System: Introduction
The male reproductive system is composed of the testes, genital ducts, accessory glands, and penis (Figure 21â€“1). The dual function of the testis is to produce spermatozoa and hormones. The genital ducts and accessory glands produce secretions that, aided by smooth muscle contractions, conduct spermatozoa toward the exterior. These secretions also provide nutrients for spermatozoa while they are confined to the male reproductive tract. Spermatozoa and the secretions of the genital ducts and accessory glands make up the semen (from Latin, meaning seed), which is introduced into the female reproductive tract through the penis. Although testosterone is the main hormone produced in the testes, both testosterone and one of its metabolites, dihydrotestosterone, are necessary for the physiology of men. Figure 21â€“1.
The male genital system. The testis and the epididymis are shown in different scales than the other parts of the reproductive system. Note the communication between the testicular lobules.
Each testis is surrounded by a thick capsule of dense connective tissue, the tunica albuginea. The tunica albuginea is thickened on the posterior surface of the testis to form the mediastinum testis, from which fibrous septa penetrate the gland, dividing it into about 250 pyramidal compartments called the testicular lobules (Figure 21â€“2). These septa are incomplete, and there is frequent intercommunication between the lobules. Each lobule is occupied by one to four seminiferous tubules enmeshed in a web of loose connective tissue that is rich in blood and lymphatic vessels, nerves, and interstitial cells, also known as Leydig cells. Seminiferous tubules produce male reproductive cells, the spermatozoa, whereas interstitial cells secrete testicular androgens. Figure 21â€“2.
Ducts of the testis and the ductus epididymis.
During embryonic development the testes develop retroperitoneally in the dorsal wall of the abdominal cavity. They migrate during fetal development and become positioned within the scrotum, at the ends of the spermatic cords. Because of this migration, each testis carries with it a serous sac, the tunica vaginalis, derived from the peritoneum. The tunic consists of an outer parietal layer and an inner visceral layer, covering the tunica albuginea on the anterior and lateral sides of the testis. Seminiferous Tubules
Spermatozoids are produced in the seminiferous tubules at a daily rate of about 2 x 108 in the adult. Each testicle has 250â€“1000 seminiferous tubules that measure about 150â€“250 m in diameter and 30â€“70 cm in length. The combined length of the tubules of one testis is about 250 m. The tubules are convoluted and have the form of loops at whose ends the lumen narrows and continues in short segments, known as straight tubules, or tubuli recti (Figure 21â€“2). These tubules connect the seminiferous tubules to an anastomosing labyrinth of epithelium-lined channels, the rete testis. About 10â€“20 ductuli efferentes connect the rete testis to the cephalic portion of the epididymis (Figure 21â€“2). The seminiferous tubules are lined with a complex stratified epithelium called germinal or seminiferous epithelium. Their outer wall is surrounded by a well-defined basal lamina and a fibrous connective tissue consisting of several layers of fibroblasts (Figure 21â€“3). The innermost layer, adhering to the basal lamina, consists of flattened myoid cells (Figure 21â€“4), which have characteristics of smooth muscle. Interstitial (Leydig) cells occupy much of the space between the seminiferous tubules (Figures 21â€“3 and 21â€“4). Figure 21â€“3.
Section of a testis showing seminiferous tubules and groups of pale-stained interstitial (Leydig) cells (arrowheads). Pararosanilineâ€“toluidine blue (PT) stain. Medium magnification.
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