Testis

The testis is the male gonad, and a pair of them lies in the scrotal sac, which hangs outside the abdominal cavity. Beyond its role in reproduction, the testis works as an endocrine gland, so it carries out two jobs at once: it is the primary male sex organ and also a producer of hormones.

Structure

Each testis is built from two kinds of tissue:

• Seminiferous tubules — the coiled tubes in which sperm are formed.
• Stromal or interstitial tissue — the supporting tissue that fills the spaces between the tubules.

Sitting in these intertubular spaces are the Leydig cells, also called interstitial cells. These cells are the endocrine part of the testis, and they secrete a family of hormones known as androgens. The chief androgen is testosterone.

What androgens do

Androgens have wide-ranging effects on the male body:

• Accessory sex organs. They direct the development, maturation and working of the male accessory sex organs, such as the epididymis, vas deferens, seminal vesicles, prostate gland and urethra.
• Male secondary sex characters. They drive muscular growth, the growth of facial and underarm (axillary) hair, aggressive behaviour and the deepening of the voice to a lower pitch.
• Spermatogenesis. Androgens strongly stimulate the formation of spermatozoa (sperm). …