21 Male Perineum and External Genitalia

Male genitalia:

The male genitalia encompasses the penis and scrotum which serve both reproductive and urinary functions. The penis consists of two parts: the cylindrical body and root:

The root is the base of the penis which attaches to the pelvic bones. The root contains two crura and a bulb. The crura are anchored to the ischial bones which form the main erectile components. The bulb, a continuous portion of the spongiosum, lies in the midline of the perineum.

The body or shaft of the penis is the cylindrical portion which extends from the root to the glans (the most distal portion). The body contains 3 columns of erectile tissue:

• Corpora cavernosa (2): These two cylindrical tissues extend from the crura and run along the dorsal (downward pointing) aspect of the penis, and maintain rigidity during erection.
• Corpus Spongiosum: The single ventral column that surrounds the urethra. This tissue prevents the urethra from being compressed allowing ejaculation.
  • The distal ends of the spongiosum forms the cap-like glans.

View the diagram below for a visual representation of the male genitalia:

The Scrotum:

The scrotum is a sac like structure which houses the testes, epididymis and the initial part of the spermatic cord:

• Testes: the primary male reproductive organ responsible for producing sperm and testosterone. Within the testes, seminiferous tubules produce millions of sperm daily via spermatogenesis.
• Epididymis: A long, coiled tube located at the posterior side of each testis where sperm matures and is stored. This tube-like structure continues to the inferior pole of the testes where it reaches the vas deferens prior to the urethra before ejaculation.
• Spermatic cord: a bundle of nerves, blood vessels, lymphatic vessels and the vas deferens (transfers sperm) which connects the testes to the abdominal cavity.

View the diagram below for a representation of the male perineum:

Scrotum temperature regulation:

The scrotum has several structural features to regulate temperature  to maintain the ideal sperm producing conditions (slightly cooler than body temperature). The dartos muscle in the scrotal wall helps to wrinkle the skin of the scrotum in cold conditions to reduce the available surface areas for heat to dissipate thus keeping the testes warm. Whereas, the cremaster muscle can lower or raise the testes depending on the outside temperature.

The diagram below outlines the muscular placements of these temperature regulating areas: