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INTRODUCTION

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ACTH Adrenocorticotropic hormone
cAMP Cyclic adenosine monophosphate
DHEA Dehydroepiandrosterone
DHT Dihydrotestosterone
FSH Follicle-stimulating hormone
GnRH Gonadotropin-releasing hormone
hCG Human chorionic gonadotropin
ICSI Intracytoplasmic sperm injection
IVF In vitro fertilization
LH Luteinizing hormone
mRNA Messenger ribonucleic acid
PDE5 Type 5 phosphodiesterase
PRL Prolactin
SHBG Sex hormone–binding globulin
TGFβ Transforming growth factor β

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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.

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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.

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ANATOMY AND STRUCTURE-FUNCTION RELATIONSHIPS

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FIGURE 12–1

Male genital system. A. The testis and the epididymis are in different scales from the other parts of the reproductive system. Observe the communication between the testicular lobules. B. Structural organization of the human seminiferous tubule and interstitial tissue. This figure does not show the lymphatic vessels frequently found in the connective tissue. (A and B reproduced with permission from Junqueira LC, Carneiro J, Kelley RO. Basic Histology. 9th ed. New York: McGraw-Hill Education; 1999.) C. Section of human testis. (C reproduced with permission from Ganong WF. Review of Medical Physiology. 20th ed. New York: McGraw-Hill Education; 2001.)

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TESTES

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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 ...

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