In most terrestrial mammals, the scrotum (pl.: scrotumsorscrota; possibly from Latinscortum, meaning "hide" or "skin")[1][2]orscrotal 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.
Diagram of 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.
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.
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.[6]
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.[8] An alternative view is that testis descent asymmetry evolved to enable more effective cooling of the testicles.[9]
Development of external genitals showing homologues from indifferent to both sexes - male on left
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.[10]
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.[11]
The scrotum regulates the temperature of the testicles and maintains it at 35 degrees Celsius (95 degrees Fahrenheit), i.e. two or three degrees below the body temperature of 37 degrees Celsius (99 degrees Fahrenheit). Higher temperatures affect spermatogenesis.[12] 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).[11]
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.[12] 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.[14] The scrotum is also considered to be an erogenous zone.[15]
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.
Unlike placental mammals, some male marsupials have a scrotum that is anterior to the penis,[18][19][20][21] which is not homologous to the scrotum of placental mammals,[22] although there are several marsupial species without an external scrotum.[23]
This article incorporates text in the public domain from page 1237 of the 20th edition of Gray's Anatomy (1918)
Media related to Scrotums at Wikimedia Commons
