The scrotum (: scrotums or scrota; possibly from Latin scortum, meaning "hide" or "skin") or scrotal sac is an anatomical male reproductive structure located at the base of the penis that consists of a suspended dual-chambered sac of skin and smooth muscle. It is present in most terrestrial male mammals. The scrotum contains the external spermatic fascia, testicles, epididymis, and ductus deferens. It is a distention of the perineum and carries some abdominal tissues into its cavity including the testicular artery, testicular vein, and pampiniform plexus. The perineal raphe is a small, vertical, slightly raised ridge of scrotal skin under which is found the scrotal septum. It appears as a thin longitudinal line that runs front to back over the entire scrotum. In humans and some other mammals, the scrotum becomes covered with pubic hair at puberty. The scrotum will usually tighten during penile erection and when exposed to cold temperatures. One testis is typically lower than the other to avoid compression in the event of an impact.
The scrotum is biologically homologous to the labia majora in females. Although present in most boreoeutherian mammals, the external scrotum is absent in fusiform marine mammals, such as whales and seals, as well as in some lineages of land mammals, such as the afrotherians, xenarthrans, and numerous families of bats, rodents, and insectivores.
Structure
Nerve supply
Blood supply
Skin and glands
Pubic hair
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 scrotum 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
Cavity of tunical albuginea
Cremaster muscle
Dartos
Ductus Deferens
Efferent ductules
Epididymis
Leydig cell
Lobule of testes
Paradidymis
Rete testes
Scrotal septum
Seminiferous tubule
Sertoli cell
Spermatic cord
Testes
Tunica albuginea of testis
Tunica vaginalis parietal layer
Tunica vaginalis visceral layer
Tunica vasculosa testis
Vas deferens
Development
Genital homology between sexes
Male sex hormones are secreted by the testes later in embryonic life to cause the development of secondary sex organs. The scrotum is developmentally homologous to the labia majora. The raphe does not exist in females. Reproductive organs and tissues develop in females and males begin 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.
Up until the eighth week after fertilization, the reproductive organs do not appear to be different between the male and female and are called in-differentiated. 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.