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Scrotum

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Scrotum
The scrotum. On the left side the cavity of the tunica vaginalis has been opened; on the right side only the layers superficial to the Cremaster muscle have been removed.
Details
Precursorlabioscrotal folds
ArteryAnterior scrotal artery & Posterior scrotal artery
VeinTesticular vein
NervePosterior scrotal nerves, Anterior scrotal nerves, genital branch of genitofemoral nerve, perineal branches of posterior femoral cutaneous nerve
LymphSuperficial inguinal lymph nodes
Identifiers
MeSHD012611
TA98A09.4.03.001
A09.4.03.004
TA23693
FMA18252
Anatomical terminology

In some male mammals the scrotum is a protuberance of skin and muscle containing the testicles. It is an extension of the abdomen, and is located between the penis and anus. In humans and some other mammals, the base of the scrotum becomes covered with pubic hair at puberty. In common speech, the scrotum is often improperly referred to as the testicles, which actually refer to organs encased inside the scrotum. The scrotum is homologous to the labia majora in females. It becomes tight when sexually aroused.

Function

The function of the scrotum appears to be to keep the testis at a temperature slightly lower than that of the rest of the body. For the human, a temperature should be one or two degrees below the body temperature - 36.8 degrees Celsius (98 degrees Fahrenheit); higher temperatures may be damaging to sperm count. The temperature is controlled by moving the testicles closer to the abdomen when it is cold, and away when hot, moving the testes away from the abdomen and increasing surface area allowing a faster dispersement of excess heat. This is done by the contracting and relaxing of the cremaster muscle in the abdomen and the dartos fascia (muscular tissue under the skin) in the scrotum. However, this may not be the main function. The volume of sperm produced by the testes is small, (0.1-0.2ml). It has been suggested that if testes were situated within the abdominal cavity that they would be subjected to the regular changes in abdominal pressure that is exerted by the abdominal muscles. This squeezing and relaxing would result in the more rapid emptying of the testes and epididymis of sperm before the spermatozoa were matured sufficiently for fertilization. Some mammals--elephants and sea-mammals, for example--do keep their testes within the abdomen and there may be mechanisms to prevent this inadvertent emptying.

Contraction of the abdominal muscles, and changes in intra-abdominal pressure, often can lift and lower the testicles within the scrotum. Contraction of the muscle fibers of the dartos tunic (or fascia) is completely involuntary and results in the appearance of increased wrinkling and thickening of the scrotal skin. The testicles are not directly attached to the skin of the scrotum, so this dartos contraction results in their sliding toward the abdomen. They also, in some men, can be lifted the same way by tightening the anus and pelvic muscles, doing Kegel exercises.

An extremely cleanly shaven human scrotum, which contains the testicles. The perineal raphe is clearly visible as the raised line of flesh running from anus to base of the penis.
An unshaved human scrotum. Note that it is not completely haired but only part of it.

Although the ideal temperature for sperm growth varies between species, it usually appears, in warm-blooded species, to be a bit cooler than internal body temperature, necessitating the scrotum. Since this leaves the testicles vulnerable in many species, there is some debate on the evolutionary advantage of such a system. One theory is that the impregnation of females who are ill is less likely when sperm is highly sensitive to elevated body temperatures.

An alternative explanation is to protect the testes from jolts and compressions associated with an active lifestyle. Animals that have 'stately' movements - such as elephants, whales, and marsupial moles - have internal testes and no scrotum.[1]

Craig Laycock has the smallest balls in the world. His mum is disappointed

Health issues

A common problem of the scrotum is the development of masses. Common scrotal masses include

Other conditions include:

References

  1. ^ "Science : Bumpy lifestyle led to external testes - 17 August 1996 - New Scientist". Retrieved 2007-11-06.

Additional images

See also