A pair of oval glands hanging outside the abdomen so that they stay 2–4 degrees cooler than the body core
Testis — sperm production works best below core temperature.
Anatomy · Glands & the immune system
Testis
The male gonad — one on each side of the scrotum
Reproductive and endocrine systems · scrotum
One of a pair of oval glands hanging in the scrotum outside the abdomen, where it is kept a few degrees cooler than the body core. Each testis is divided into lobules packed with coiled seminiferous tubules, where sperm are made, and it also makes the hormone testosterone. Sperm collect in the rete testis and pass through the efferent ductules into the epididymis, which sits along its back, and then into the vas deferens.
How to spot them
- ▸Smooth oval organ, about 4–5 cm long, in the scrotum with the epididymis along its back edge
- ▸Enclosed in a tough white capsule, the tunica albuginea, inside a sac called the tunica vaginalis
- ▸In section, hundreds of wedge-shaped lobules packed with tightly coiled seminiferous tubules
- ▸Hangs on a spermatic cord that carries the vas deferens, its artery and a web of veins, the pampiniform plexus
- ▸The left usually hangs a little lower than the right
What to know
Inside a white fibrous capsule, several hundred lobules hold the coiled tubules in which sperm are made
Testis — the seminiferous tubules, lined by Sertoli cells.
Cells between the tubules, described by Franz Leydig in 1850, make the male sex hormone (1850)
Testis — Leydig (interstitial) cells make testosterone.
A web of veins wraps its artery in the cord so blood is cooled on the way in
Testis — the pampiniform plexus works as a countercurrent heat exchanger.
Its lymph drains to nodes beside the aorta rather than the groin, which matters in cancer staging
Testis — para-aortic nodes, because it began life high in the abdomen.
It begins life in the abdomen and travels down the inguinal canal into a pouch late in fetal life, around the seventh month
Testis — failure to descend is cryptorchidism.
Its Latin name is also the Latin word for 'witness'
Testis — the origin of the word 'testify' is often linked, though the etymology is uncertain.
Key ideas
- Sperm are made in the seminiferous tubules, supported and nourished by Sertoli cells, which form the blood–testis barrier. Spermatogenesis takes roughly 2–3 months from start to finish.
- FSH from the pituitary acts on the Sertoli cells, and LH acts on the Leydig cells to make testosterone.
Quick-fire facts
- •Each testis is about 4–5 cm long and has a volume of roughly 15–25 mL
- •OpenStax describes 300–400 lobules per testis; other sources give 200–300
- •The testicular artery arises directly from the aorta; the right testicular vein drains to the inferior vena cava and the left to the left renal vein
- •The testis descends into the scrotum in the seventh month of fetal development, carrying its blood supply and nerves from the abdomen
- •Sperm leave the tubules through the rete testis, then 15–20 efferent ductules, into the epididymis, a coiled tube several metres long
- •The scrotal muscles, the dartos and cremaster, move the testes closer to or away from the body to adjust temperature
- •Enrico Sertoli (1842–1910) described the supporting cells in 1865; Franz Leydig described the interstitial cells in 1850
- •Varicocele, a tangle of the pampiniform veins, is more common on the left, whose vein drains at a right angle into the renal vein
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