Testicle

The testicles, known medically as testes (singular testis), are the male generative glands in animals. In mammals, the testicles are paired bodies that are contained within a pouch termed the scrotum.

Like the ovaries to which they are homologous, testicles are members of both the reproductive system (being gonads - see sex organs) and the endocrine system (being endocrine glands). The respective functions of the testicles are:

producing sperm (spermatozoa)
producing male sex hormones - mainly testosterone

Under a tough fibrous shell, the tunica albuginea, the testis contains very fine coiled tubes called the seminiferous tubules. The tubes are lined with a layer of cells that from puberty until old-age produce sperm cells. The seminiferous tubules lead to the epididymis, where newly created sperm cells mature, and then into vas deferens (also called the ductus deferens) that opens into the urethra. During sexual intercourse, the sperm cells move through the ejaculatory duct and into the prostatic urethra, where the prostate, through muscular contractions, ejaculates the sperm, mixed with other fluids, out through the penis.

Between the seminiferous tubules are special cells called interstitial cells (Leydig cells) where testosterone and other androgens are formed.

The testicles are well-known to be very sensitive to impact and injury. This has been a rich source of humor for jokes and comedic routines.

The most important diseases of testicles are:

inflammation of the testicles, called orchitis
testicular cancer and other neoplasms
hydrocele
inflammation of the epididymis, called epididymitis
spermatic cord torsion also called testicular torsion
varicocele

If a testicle is medically removed (orchidectomy) or destroyed through disease or injury, testicular prostheses are available to mimic the appearance and feel of the missing testicle.

Both components of the testicle, sperm-forming and endocrine, are under control of gonadotropic hormones - lutenizing hormone (LH) and follicle-stimulating hormone (FSH), that are produced by the anterior pituitary.