Histology of the male reproductive system

Testis

The testes (sing. testis) are the male gonads that lie within the scrotum. They reside within a connective tissue layer known as the tunica albuginea and tunica vaginalis which are further enveloped by the layers of the spermatic cord.

Each testis is composed of approximately 250 pyramid shaped lobules separated by septae of connective tissue that extend inward from the tunica albuginea. Each lobule contains one to four convoluted seminiferous tubules, where sperm production (spermatogenesis) occurs. Supporting cells within the testes secrete hormones, primarily androgens such as testosterone.

Sustentacular (Sertoli) cells are large columnar somatic cells that span from the basement membrane to the lumen of the seminiferous tubules. This gives structural organization to the tubules. They also have a supporting function and aid in the process of spermatogenesis.

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Epididymis

The epididymis is a crescent-shaped organ and an essential component of the male reproductive system. It lies in close proximity to the testis, positioned along its superior and posterior surfaces. Functionally, it is a site of sperm storage and maturation until the time of discharge to the ductus deferens (vas deferens).

The epididymis consists of the efferent ductules and the duct of the epididymis as well as associated vessels, smooth muscles and coverings of connective tissue. Structurally, the epididymis is divided into a head, a body and a tail, with the efferent ductules occupying the head and the duct of the epididymis forming its body and tail.

Both the efferent ductules and duct of epididymis are covered with pseudostratified columnar epithelium. Two types of specialized cells can be found here, principal and basal cells. Additionally, halo cells, a type of lymphocytes, reside throughout the epididymal epithelium and serve as the primary immune cells in the epididymis.

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Spermatic cord

The spermatic cord is a tubular structure present in males, which forms a conduit between the abdominal cavity and the testis. It houses the ductus deferens and a collection of blood vessels, including the testicular artery and vein, the pampiniform plexus, and nerves which run to and from the testis.

The spermatic cord is lined with pseudostratified columnar epithelium with sterocilia. It resembles the epithelium of the epididymis, but the cells are not as tall. The columnar cells usually have elongated nuclei in contrast to the spherical nuclei of the basal cells.

The ductus deferens is characterized by a thickened muscular coat of 3 layers (inner longitudinal, outer longitudinal, middle circular layer). Between the epithelium and the inner longitudinal smooth muscle layer, lies a moderately thick cellular layer of loose connective tissue, known as the lamina propria. There is no submucosa present here.

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Penis

The penis is a copulatory organ of the external genitalia of males. It consists of three parts; root (radix), body (shaft) and glans. 

The penis is composed of three cylindrical columns of erectile tissue, namely the two corpora cavernosa and the corpus spongiosum, which are bound together by a dense fibroelastic layer called the tunica albuginea. The corpora contain irregular vascular spaces, lined by vascular endothelium. These fill with blood during erection, while the corpus spongiosum protects the urethra from compression by the engorged corpora cavernosa.

The tunica albuginea is surrounded by a layer of superficial fascia that contains connective tissue, prominent blood vessels, and nerves. Surrounding the superficial fascia is the outermost sheath of penile skin which is covered with stratified squamous keratinized epithelium. Unless circumcised, it extends over the glans as the prepuce or foreskin, which acts as a retractable protective fold of skin. 

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Prostate

The prostate is an accessory organ of the male reproductive system. It is a large and dense exocrine gland which is responsible for secreting a white alkaline fluid that makes up about 30 to 50% of the total seminal fluid volume (semen).

The prostate consists of approximately 70% glandular tissue and 30% fibromuscular stroma, and based on this composition, it can be divided into two parts: a fibromuscular part and a glandular part. 

The fibromuscular stroma (fibromuscular part) surrounds the anterior surface of the prostate and is composed of dense irregular connective tissue with a mix of smooth muscle fibers and elastic fibers. 

Its glandular part consists of four zones: central, peripheral, transitional and periurethral.

The tubuloalveolar glands in the prostate vary widely in size and have lumens that are lined by connective tissue folds. The connective tissue foldings result in the acini appearing highly irregular. Generally, they are lined by simple columnar or pseudostratified epithelium.

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• Gametogenesis
• Spermatogonia
• Spermatozoa