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SUMMARY OF KEY POINTS
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The Male Reproductive System SUMMARY OF KEY POINTS Testes
In each testis approximately each of 250 lobules contains one or more very long, convoluted seminiferous tubules in a sparse, vascular stroma containing testosterone-producing interstitial cells (of Leydig).
Seminiferous tubules consist of spermatogenic epithelium containing columnar Sertoli cells, each of which supports and nourishes many germ cells embedded at its surface.
Tight junctions between Sertoli cells establish two compartments within seminiferous tubules: a basal compartment with spermatogonia and an adluminal compartment with spermatocytes and spermatids.
Sertoli cells also produce androgen-binding protein, which concentrates testosterone, phagocytose shed debris from differentiating spermatids, and secrete fluid, which carries sperm along the tubules.
Progenitor cells called spermatogonia undergo mitosis and give rise to primary spermatocytes, which undergo a first meiotic division to form haploid secondary spermatocytes.
After a very short interval, secondary spermatocytes undergo the second meiotic division to produce small, round spermatids, which differentiate while still associated with Sertoli cells.
A spermatid undergoes spermiogenesis by greatly condensing its nucleus, forming a long flagellum with a surrounding mitochondrial middle piece, and forming a perinuclear acrosomal cap.
From the seminiferous tubules, sperm enter the short straight tubules, which lead to channels of the rete testis in the mediastinum testis, then move via 15 or 20 efferent ductules where fluid is absorbed.
Excretory Genital Ducts From efferent ductules sperm move into and through epididymal ducts in the head, body, and tail of epididymis, also located in the scrotum, for their final maturation and short storage prior to ejaculation.
The epididymis is lined by pseudostratified columnar epithelium containing principal cells, which have long stereocilia; along its length the number of surrounding smooth muscle layers increases.
At ejaculation, the body and tail of the epididymis are emptied into the ductus (vas) deferens, also lined by pseudostratified columnar epithelium with three thick layers of smooth muscle for peristalsis.
Accessory Glands Most semen is produced by the paired seminal vesicles (glands), characterized by numerous thin folds of secretory mucosa; a duct from each seminal vesicle joins a ductus deferens as an ejaculatory duct.
Inside the medial prostate gland, the two ejaculatory ducts and dozens of ducts from tubuloacinar prostatic glands merge with the urethra that transports semen through the penis.
Semen components from the seminal vesicles nourish sperm (eg, fructose), activate ciliary and muscle activity in the female reproductive tract (prostaglandins), and control the product’s viscosity for sperm release.
Penis The penis contains two dorsal corpora cavernosa and a periurethral corpus spongiosum, all composed of vascular cavernous tissue and small amounts of surrounding smooth muscle and helicine arteries.
For erection parasympathetic stimulation relaxes muscle of the small helicine arteries and adjacent tissues, allowing vessels of the cavernous tissue to fill with blood; the enlarging corpora compress the venous drainage, producing further enlargement and turgidity in the three ...