Scrotum

Lore & Background

The scrotum develops during the fifth week after fertilization, when the genital ridge grows behind the peritoneal membrane. By the sixth week, primary sex cords form within the enlarging genital ridge. Testosterone secretion starts during week eight, peaks at week 13, and declines by the end of the second trimester, causing masculinization of the labioscrotal folds into the scrotum. The scrotal raphe forms when the embryonic urethral groove closes by week 12. During puberty, increased testosterone secretion causes darkening of the skin and development of pubic hair on the scrotum.

Reader's Guide

The scrotum's primary function is temperature regulation of the testicles, maintaining them at 35 degrees Celsius, two to three degrees below body temperature, which is critical for spermatogenesis. This is achieved by the cremaster muscle and dartos fascia moving the testicles closer to or further from the abdomen depending on ambient temperature. The scrotum also tightens and thickens during sexual arousal. Having the scrotum outside the abdominal cavity may prevent emptying of testes before sperm maturation and protect against jolts and compressions. The scrotum is considered an erogenous zone and may provide friction during intercourse. Clinically, the scrotum can develop various diseases and injuries. In society, common slang terms include ballsack, nutsack, and teabag. Scrotoplasty is a sex reassignment surgery for trans men or a reconstructive procedure. Cock and ball torture and sack tapping are practices involving the scrotum. The scrotum is a synapomorphy of boreoeutherians, secondarily lost in some mammals like hippopotamuses, rhinoceroses, and whales.

Did You Know?

• The scrotum is homologous to the labia majora in females.
• The left testis is typically lower than the right in humans, possibly to avoid compression or aid cooling.
• The scrotum regulates testicle temperature to 35°C (95°F), below body temperature.
• The scrotum has been secondarily lost in hippopotamuses, rhinoceroses, hedgehogs, moles, pangolins, tapirs, numerous bats and rodents, whales, dolphins, and seals.