Scrotum

In most terrestrial mammals, the scrotum (: scrotums or scrota; possibly from Latin scortum, meaning "hide" or "skin") 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.

Structure
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.

Skin and glands

 * Sebaceous glands
 * Apocrine glands
 * Smooth muscle

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.

Lymphatic system
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.

Asymmetry
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. An alternative view is that testis descent asymmetry evolved to enable more effective cooling of the testicles.

Internal structure


Additional tissues and organs reside inside the scrotum and are described in more detail in the following articles:


 * Appendix of epididymidis
 * Cremaster muscle
 * Dartos fascia
 * Efferent ductules
 * Epididymis
 * Leydig cell
 * Lobules of testis
 * Paradidymis
 * Rete testes
 * Scrotal septum
 * Seminiferous tubule
 * Sertoli cell
 * Spermatic cord
 * Testicle
 * Tunica albuginea of testis
 * Tunica vaginalis
 * Tunica vasculosa testis
 * Vas deferens

Development
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.

Scrotal growth and puberty
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.

Function
The scrotum regulates the temperature of the testicles and maintains it at 35 C, i.e. two or three degrees below the body temperature of 37 C. 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.

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. The scrotum is also considered to be an erogenous zone.

Society and culture
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.

Other animals
A scrotum is present in all boreoeutherian land mammals except hippopotamuses, rhinoceroses, hedgehogs, moles, pangolins, tapirs, and numerous families of bats and rodents. 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.

Unlike placental mammals, some male marsupials have a scrotum that is anterior to the penis,   which is not homologous to the scrotum of placental mammals, although there are several marsupial species without an external scrotum.

The scrotum is also absent in marine mammals, such as whales, dolphins, and seals, as well as in lineages of other land mammals, such as the afrotherians (elephants, aardvarks, etc.) and xenarthrans (armadillos, anteaters, and sloths).

Clinical significance
A study has indicated that use of a laptop computer positioned on the lap can negatively affect sperm production.

Diseases and conditions
The scrotum and its contents can develop many diseases and can incur injuries. These include:


 * Candidiasis (yeast infection)
 * Sebaceous cyst
 * Epidermal cyst
 * Hydrocele testis
 * Hematocele
 * Molluscum contagiosum
 * Spermatocele
 * Paget's disease of the scrotum
 * Varicocele - enlargement of the pampiniform venous complex
 * Inguinal hernia
 * Epididymo-orchitis
 * Testicular torsion
 * Pruritus scroti - irritation of the scrotum (itchiness)
 * Genital warts - sexually transmitted infection
 * Testicular cancer
 * Dermatitis
 * Undescended testes
 * Chyloderma - swollen scrotum caused by a lymphatic obstruction
 * Mumps
 * Scabies
 * Herpes - sexually transmitted infection
 * Pubic lice
 * Chancroid (Haemophilus ducreyi) - sexually transmitted infection
 * Chlamydia (Chlamydia trachomatis) - sexually transmitted infection
 * Gonorrhea (Neisseria gonorrhoeae) - sexually transmitted infection
 * Granuloma inguinale or (Klebsiella granulomatis)
 * Syphilis (Treponema pallidum) - sexually transmitted infection
 * Scrotal eczema
 * Scrotal psoriasis disease
 * Riboflavin deficiency
 * Chimney sweeps' carcinoma (scrotal cancer)