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Male reproductive system is located in pelvic region of the body. It includes following organs:

• A Pair of Testes
• System of ducts (Epididymis, Ductus deferens, Ejaculatory ducts, and Urethra)
• Accessory sex glands (Seminal vesicles, Prostate, and Bulbourethral glands),
• External genitalia like Scrotum and the Penis.

Testes

• Testes are the male gonads (primary sex organ which produce gametes) which produce sperm and secrete sex hormones. Also called as testicles.
• Each testis (singular) is oval in shape, length about 4 to 5 cm and a width of about 2 to 3 cm.
• Testes are situated outside the abdominal cavity within a pouch or bag like supporting structure called Scrotum. It consists of loose skin that hangs scrotum from the root of the penis.
• Externally, scrotum is like a single pouch of skin separated into lateral portions by a median ridge called Raphe. Internally, scrotal septum (consisting of Dartos muscles) divides scrotum into two sacs, each of which contains single testis.
• Sperm production (spermatogenesis) in testes requires a 2–2.5, 3ºC low temperature than normal body temperature. Scrotum helps in maintaining this low temperature of the testes by contraction of its dartos muscle. In response to cold temperatures, scrotal muscles contract and tighten (wrinkled) which moves the testes close to the body, where they can absorb body heat and reduces heat loss. In warm conditions, muscles got relaxed.

Structure of Testis

• Testis is covered by two dense coverings: outer is Tunica vaginalis and inner is Tunica albuginea.
• Tunica albuginea extends inwards in testis and forms septa that divide the testis into a series of internal compartments called testicular lobules. Each testis has about 250 testicular lobules. Each lobule contains one to three tightly coiled tubules called seminiferous tubules where sperms are produced. The process by which the seminiferous tubules of the testes produce sperm is called spermatogenesis.
• Seminiferous tubules contain two types of cells:

1. Spermatogonia or Spermatogenic cells (male germ cells or sperm-forming cells)
2. Sertoli cells or Sustentacular cells

• Spermatogonia develop from primordial germ cells during the embryo development. Spermatogonia (Male germ cells) remain dormant during childhood and begin producing sperm only at puberty.
• Sertoli cells are found embedded among the spermatogenic cells in the seminiferous tubules. Sertoli cells are large in size and they extend from the membrane to the lumen of the seminiferous tubule.
• Functions of Sertoli cells: 1. Provide nutrition to the germ cells in all stages of sperm formation.

2. Helps in release of sperm into the lumen of the seminiferous tubule.
3. Produce fluid for sperm transport.
4. Secrete hormone inhibin, and regulate the effects of testosterone and FSH (follicle-stimulating hormone).
5. Protects spermatogenic cell by forming blood-testis barrier to prevent an immune response against the spermatogenic cell’s surface antigens which are recognized as “foreign” by the immune system.

• Spaces between adjacent seminiferous tubules called as Interstitial spaces, which contain small
  blood vessels and clusters of cells called interstitial cells or Leydig cells. These cells synthesize and secrete testicular hormones called Androgens. Testosterone is the most prevalent androgen.
• Androgen is a hormone that promotes the development of masculine characteristics, and responsible for man’s sexual drive.

NOTE: Cryptorchidism: Condition in which testes fail to descend into the scrotum during embryonic development. Results in insterility.