Testes: Gross Anatomy

The testes, also called testicles, are the male gonads that produce sperm and hormones essential for reproduction. Each testis weighs 10 to 15 grams and measures approximately 5 cm long, 3 cm wide, and 2.5 cm thick. They are housed within the scrotum, a sac-like structure located beneath the penis that provides protection and temperature regulation.

The tunica albuginea is a dense connective tissue layer that surrounds each testis, providing structural support and protection. It is externally covered by the tunica vaginalis, a serous membrane that lines the scrotum and helps reduce friction between the testes and surrounding structures, allowing them to move freely.

The scrotum maintains testicular temperature 2 to 3 degrees Fahrenheit lower than the rest of the body through two mechanisms. The dartos muscle wrinkles the scrotal skin to reduce heat loss, while the cremaster muscles, made of skeletal muscle fibers, contract during cold temperatures or sexual arousal to pull the testes closer to the body, protecting them from excessive cooling.

The scrotal septum is a fibrous partition composed of subcutaneous fascia and smooth muscle that divides the scrotum into two separate chambers, each housing one testis. This structural division prevents the testes from moving freely between sides and helps maintain independent temperature regulation for each gonad.

The scrotal wall consists of a thin layer of skin, superficial fascia, and muscle layers that provide physical protection to the testes. The dartos muscle runs along the subcutaneous layer and causes wrinkling of the scrotal surface, while the cremaster muscles extend from the abdominal wall to assist in thermoregulation and support.

Temperature regulation is essential because the testes require a cooler environment than the rest of the body for optimal sperm development and production. The scrotum's thermoregulatory mechanisms maintain this ideal temperature differential, ensuring the testes function effectively and support male fertility and reproductive capacity.

The dartos muscle, composed of smooth muscle in the subcutaneous layer, wrinkles the scrotal skin to reduce heat loss passively. The cremaster muscles, made of skeletal muscle fibers, actively contract in response to cold or sexual arousal, pulling the testes upward toward the body. Together, these muscles provide dual thermoregulatory control to maintain optimal testicular conditions.