The testicles (testes) are the main male reproductive organs. They produce sperm and testosterone. They are egg-shaped and about 5 cm long. The testicles are covered by a sac of skin called the scrotum. The scrotum hangs below the base of the penis, between the legs.
Structure
Each testicle is covered by a tough, fibrous capsule that has an outer layer and an inner layer. The testicle is divided into about 250 lobules. Each lobule contains 1–4 tubules lined by germ cells, which develop into sperm cells. The germ cells are supported by stromal cells called Sertoli or 'nurse' cells found in the lining of each tubule. Specialised hormone producing stromal cells called Leydig cells are located in the supporting tissue between the tubules. Ducts in the testicles form a network called the rete testis. Ducts from the rete testis join to form a tightly coiled tube called the epididymis. The epididymis joins a single, wide duct called the vas deferens (ductus deferens). A cord-like structure, called the spermatic cord, extends from each testicle to the abdomen. The spermatic cord contains the vas deferens, along with blood vessels and nerves.
Lymph fluid drains from the testicle into a group of lymph nodes called the retroperitoneal lymph nodes. These nodes are located in the back of the abdomen.
Function
The testicles are made up of 2 main types of cells: germ cells and stromal cells
Germ cells
The germ cells in the testicles produce sperm cells.
- Sperm cells move from the testicle to the epididymis, where they are stored. During ejaculation, sperm cells are carried to the urethra by the vas deferens.
- Along the way, fluids produced by the seminal vesicles and the prostate gland are emptied into the ducts. These fluids mix with the sperm cells to create semen.
- The semen is expelled from the body through the urethra.
Stromal cells
Specialized stromal cells (supporting tissue cells) called Leydig cells make male sex hormones, mostly testosterone. Testosterone controls:
- reproduction
- sex drive (libido)
- male physical traits, such as:
- development of reproductive organs and genitals
- deep voice
- body and facial hair
- increase in muscle and bone strength
Other specialized stromal cells called Sertoli cells provide support and nourishment to the sperm.