Testicle

Image:Male anatomy.png

The testicles, known medically as testes (singulartestis), are the male generative glands in animals. Male mammalshave two testicles, which are often contained within an extension of the abdomencalled the scrotum.

In mammals, the testes are located outside of the body, as they are suspended by the spermatic cord and within the scrotum. This is due to the fact that spermatogenesisis more efficient at a temperature somewhat less than the core body temperature of 37 degrees Celsius (98.6 degrees Fahrenheit). The cremasteric muscle is part of the spermatic cord. When this muscle contracts, the cord is shortened and the testicle is moved closer up toward the body, which provides slightly more warmth to maintain optimal testicular temperature. When the temperature needs to be lowered, the cremasteric muscle relaxes and the testicle is lowered away from the warm body and are able to cool. This phenomenon is known as the cremasteric reflex. It also occurs in response to stress (the testicles rise up toward the body in an evolutionary effort to protect them in a fight) and they also contract during orgasm.

It is normal for one testis to hang lower than the other (usually the left). This is primarily due to differences in the vascular anatomical structure on the right and left sides. It is thought that this is another evolutionary development that protects each testis from bouncing off the other.

Function

Like the ovaries(to which they are homologous), testicles are components of both the reproductive system(being gonads) and the endocrine system(being endocrine glands). The respective functions of the testicles are:

• producing sperm(spermatozoa)
• producing male sex hormones, of which testosteroneis the best-known

Both functions of the testicle, sperm-forming and endocrine, are under control of gonadotropic hormones produced by the anterior pituitary:

• luteinizing hormone(LH)
• follicle-stimulating hormone(FSH)

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 pubertyinto old-age, produce sperm cells. The sperm travel from the seminiferous tubules to the rete testis, the efferent ducts, and then to the epididymiswhere 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 ductand 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 impregnationof a fertile female of the same species(or a sufficiently close one), via sexual intercoursewith her.

Image:Transversetestis.png

Between the seminiferous tubules are special cells called interstitial cells (Leydig cells) where testosteroneand other androgensare 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 polygamousthan monogamous. Production of testicular output is also larger in the polygamousanimal, possibly a spermatogenic competitionfor 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 ultrasoundimaging. The volume is then calculated, e.g., using the formula for ellipsoids: π/6 × length × width². 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 gonadotrophic-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:

• inflammation of the testicles, called orchitis
• testicular cancerand other neoplasms
• accumulation of clear fluid around a testicle, called hydrocele testis
• inflammation of the epididymis, called epididymitis
• spermatic cord torsionalso called testicular torsion
• varicocele[1]- swollen vein to the testes, usually affecting the left testicle
• Anorchidism is the absence of one or both testicles.

The removal of one or both testicles is termed

• orchidectomy, in medicine (where orchiectomy and orchectomy are synonymous), and
• castrationin general use, especially when done for the benefit of others than the subject, for example, to produce a high-voiced castratofrom the castration of a pre-pubescentboy

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. Although these prosthetic testicles mimic the human testicle accurately, many believe the real testicle to be more satisfying.

See also

• Anorchia
• cryptorchidism(cryptorchismus)
• Polyorchidism
• infertility
• List of homologues of the human reproductive system
• orchidometer
• spermatogenesis
• sterilization (surgical procedure), vasectomy
• Epididymis
• Spermatic cord
• Penis
• Ovary
• WikiSaurus:testicles— the WikiSauruslist of synonyms and slang words for testicles in many languages

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This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Testicle Wikipedia article Testicle.