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The testicles, known medically as '''testes''' ( Singular '''testis'''), are the male Generative Gland s in Animal s. Male Mammal s have two testicles, which are often contained within an extension of the Abdomen called the Scrotum . In s to cool the testes internally, but later studies revealed that birds' testes function at core body temperature. {Link without Title} It is most common for one testicle to hang lower than the other. The percentage of people with a lower hanging right testicle or left testicle is about equal. This is primarily due to differences in the vascular anatomical structure on the right and left sides. FUNCTION Like the Ovaries (to which they are Homologous ), testicles are components of both the Reproductive System (being Gonad s) and the Endocrine System (being Endocrine Gland s). The respective functions of the testicles are:
Both functions of the testicle, sperm-forming and endocrine, are under control of gonadotropic hormones produced by the anterior Pituitary :
STRUCTURE Under a tough fibrous shell, the Tunica Albuginea , the testis contains very fine coiled tubes called the ''seminiferous tubules''. The tubes are lined with a layer of cells that, from Puberty into old-age, produce sperm cells. The sperm travel from the seminiferous tubules to the Rete Testis , the Efferent Ducts , and then to the Epididymis where newly-created sperm cells mature (see Spermatogenesis ). The sperm move into the Vas Deferens (also called the ductus deferens), which opens into the Urethra . Upon any sufficient Sexual Arousal , the sperm cells move through the Ejaculatory Duct and into the prostatic urethra, where the Prostate , through muscular contractions, ejaculates the sperm, mixed with other fluids, out through the Penis . The genital anatomy described here, along with the neuroanatomy and hormonal systems that enable it to perform ejaculation, have as primary evolutionary functions the Impregnation of a fertile female of the same Species (or a sufficiently close one), via Sexual Intercourse with her. Between the seminiferous tubules are special cells called Interstitial Cells (Leydig cells) where Testosterone and other Androgens are formed. TESTICULAR SIZE Testicular size in relation to body weight varies widely. In the mammalian kingdom, there is a tendency for testicular size to be larger when the species is more likely to be Polygamous than Monogamous . Production of testicular output is also larger in the Polygamous animal, possibly a Spermatogenic Competition for survival. In normal adult human males, testicular size ranges from the lower end of around 14 cm³ to the upper end larger than 35 cm³. Measurement in the living adult is done in two basic ways: (1) comparing the testicle with ellipsoids of known sizes ( Orchidometer ), or (2) measuring the length, depth and width with a ruler, a pair of calipers or Ultrasound imaging. The volume is then calculated, e.g., using the formula for ellipsoids: π/6 × length × width&2. Usually right and left testicles have about the same size, but not exactly the same size. To some extent, it is possible to change testicular size. Short of direct injury or subjecting them to adverse conditions, e.g., higher temperature than they are normally accustomed to, they can be shrunk by competing against their intrinsic hormonal function through the use of externally administered steroidal hormones. Similarly, stimulation of testicular functions via gonadotropic-like hormones may enlarge their size. HEALTH ISSUES The testicles are well-known to be very sensitive to Impact And Injury . The most important diseases of testicles are:
The removal of one or both testicles is termed
At least for humans, testicular prostheses are available to mimic the appearance and feel of one or both testicles, when absent as from injury or medical treatment. There have also been some instances of their implanting in dogs. HERALDRY Testes appeared in s counterchanged''. {Link without Title} SEE ALSO
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