++
++
The testes contain two major components that are structurally separate and serve different functions. The Leydig cells, or interstitial cells, produce sex steroid hormones and comprise one of the two major endocrine cells of the testes. The primary secretory product of Leydig cells, testosterone, is responsible either directly or indirectly for embryonic differentiation along male lines of the external and internal genitalia, male secondary sexual development at puberty, and maintenance of libido and potency in the adult male. The Leydig cells make 4 to 6 mg of testosterone daily. The seminiferous tubules comprise the bulk of the testes and are responsible for the production of approximately 30 million spermatozoa per day during male reproductive life (puberty to death). The Sertoli cells, the nurse cells of the seminiferous tubules, are the other major endocrine cells, and they produce inhibin B, anti-Müllerian hormone (AMH) and products important for regulating spermatogenesis.
++
The two testicular components are interrelated, and both require an intact hypothalamic-pituitary axis for initiation and maintenance of their function. In addition, accessory genital structures (including the epidydimi) are required for the functional maturation and transport of spermatozoa. Thus, disorders of the testes, hypothalamus, pituitary, or accessory structures may result in abnormalities of androgen or gamete production, infertility, or a combination of these problems.
+++
ANATOMY AND STRUCTURE-FUNCTION RELATIONSHIPS
+
++
++
The adult testis is a prolate spheroid with a normal volume that ranges from 15 to 30 cc. The mean volume is about 20 cc. The average length measures 3.5 to 5.5 cm, and the average width is 2.0 to 3.0 cm. The testes are located within the scrotum, which not only serves as a protective envelope but also helps to maintain the testicular temperature approximately 2°C below the body ...