In most terrestrial mammals, the scrotum (: scrotums or scrota; possibly from Latin scortum, meaning "hide" or "skin")[1] [2] or scrotal sac is a part of the external male genitalia located at the base of the penis. It consists of a sac of skin containing the external spermatic fascia, testicles, epididymides, and vasa deferentia. The scrotum will usually tighten when exposed to cold temperatures.
The scrotum is homologous to the labia majora in females.
In regards to humans, the scrotum is a suspended dual-chambered sac of skin and muscular tissue containing the testicles and the lower part of the spermatic cords. It is located behind the penis and above the perineum. The perineal raphe is a small, vertical ridge of skin that expands from the anus and runs through the middle of the scrotum front to back. The scrotum is also a distention of the perineum and carries some abdominal tissues into its cavity including the testicular artery, testicular vein, and pampiniform plexus.
| Nerve | Surface[3] | |
|---|---|---|
| anterolateral | ||
| Anterior scrotal nerves (from ilioinguinal nerve) | anterior | |
| Posterior scrotal nerves (from perineal nerve) | posterior | |
| inferior |
The skin on the scrotum is more highly pigmented in comparison to the rest of the body. The septum is a connective tissue membrane dividing the scrotum into two cavities.[4]
The scrotal lymph initially drains into the superficial inguinal lymph nodes, this then drains into the deep inguinal lymph nodes. The deep inguinal lymph nodes channel into the common iliac, which ultimately releases lymph into the cisterna chyli.
One testis is typically lower than the other, which is believed to function to avoid compression in the event of impact; in humans, the left testis is typically lower than the right.[6] An alternative view is that testis descent asymmetry evolved to enable more effective cooling of the testicles.[7]
Additional tissues and organs reside inside the scrotum and are described in more detail in the following articles:
See main article: Development of the reproductive system. During the fifth week after fertilization, the genital ridge grows behind the peritoneal membrane. By the sixth week, string-like tissues called primary sex cords form within the enlarging genital ridge. Externally, a swelling called the genital tubercule appears over the cloacal membrane.
Testosterone secretion starts during week eight, reaches peak levels during week 13 and eventually declines to very low levels by the end of the second trimester. The testosterone causes the masculinization of the labioscrotal folds into the scrotum. The scrotal raphe is formed when the embryonic, urethral groove closes by week 12.
Though the testes and scrotum form early in embryonic life, sexual maturation begins upon entering puberty. The increased secretion of testosterone causes the darkening of the skin and development of pubic hair on the scrotum.
The scrotum regulates the temperature of the testicles and maintains it at 35C, i.e. two or three degrees below the body temperature of 37C. Higher temperatures affect spermatogenesis. Temperature control is accomplished by the smooth muscles of the scrotum moving the testicles either closer to or further away from the abdomen dependent upon the ambient temperature. This is accomplished by the cremaster muscle in the abdomen and the dartos fascia (muscular tissue under the skin that makes the scrotum appear wrinkly).
During sexual arousal, the scrotum will also tighten and thicken in the course of penile erection.[8]
Having the scrotum and testicles situated outside the abdominal cavity may provide additional advantages. The external scrotum is not affected by abdominal pressure. This may prevent the emptying of the testes before the sperm were matured sufficiently for fertilization. Another advantage is it protects the testes from jolts and compressions associated with an active lifestyle. The scrotum may provide some friction during intercourse, helping to enhance the activity.[9] The scrotum is also considered to be an erogenous zone.[10]
Common slang terms for the scrotum are ballsack, nutsack, and teabag.
Some men will get a piercing on the skin of the scrotum, any of which is called a hafada (e.g., scrotal ladder). Side-to-side or front-to-back piercings that pass through the scrotum are known as transscrotal piercings.
Scrotoplasty is a type of sex reassignment surgery to create a scrotum for trans men by using tissue from the labia majora or a type of plastic surgery to reconstruct it.
A scrotum is present in all boreoeutherian land mammals except hippopotamuses, rhinoceroses, hedgehogs, moles, pangolins, tapirs, and numerous families of bats and rodents.[11] The anus is separated from the scrotum by the perineum in these mammals. The testicles remain in the body cavity in all other vertebrates, including cloacal animals.[12]
Unlike placental mammals, some male marsupials have a scrotum that is anterior to the penis,[13] [14] [15] [16] which is not homologous to the scrotum of placental mammals,[17] although there are several marsupial species without an external scrotum.[18]
The scrotum is also absent in marine mammals, such as whales, dolphins, and seals,[19] as well as in lineages of other land mammals, such as the afrotherians (elephants, aardvarks, etc.), xenarthrans (armadillos, anteaters, and sloths),[20] [11] and monotremes.[21] [22]
A study has indicated that use of a laptop computer positioned on the lap can negatively affect sperm production.[23] [24]
The scrotum and its contents can develop many diseases and can incur injuries. These include: