The testis is the male gonad in animals. Like the ovaries to which they are homologous, testes are components of both the reproductive system and the endocrine system. Thee testes produce sperm (spermatogenesis) and androgens, primarily testosterone. Both functions of the testis are influenced by gonadotropic hormones produced by the anterior pituitary gland. Luteinizing hormone results in testosterone release. The presence of both testosterone and follicle-stimulating hormone (FSH) is needed to support spermatogenesis.
Almost all healthy male vertebrates have two testes. In mammals, the testes are often contained within an extension of the abdomen called the scrotum. In mammals with external testes, it is most common for one testicle to hang lower than the other. While the size of the testis varies, it is estimated that 21.9% of men have one higher-positioned testis, while 27.3% of men have reported equally-positioned testicles.
The tough membranous shell called the tunica albuginea contains very fine coiled tubes called seminiferous tubules. These are lined with a layer of germ cells that develop into sperm cells (also known as spermatozoa or male gametes) from puberty into old age. The developing sperm travels through the seminiferous tubules to the rete testis located in the mediastinum testis, to the efferent ducts, and then to the epididymis where newly-created sperm cells mature. The sperm moves into the vas deferens and is eventually expelled through the urethra, via the urethral orifice through muscular contractions.
Leydig cells located between seminiferous tubules produce and secrete testosterone and other androgens important for sexual development and puberty, including secondary sexual characteristics such as facial hair and sexual behavior. They also support libido, spermatogenesis, and erectile function. In addition, testosterone controls testicular volume. The sertoli cells are the testes’ somatic cells, necessary for testis development and spermatogenesis.
A diagram of the major components of an adult human testis, including the following numbered items: 1. Tunica albuginea, 2. Septula testis, 3. Lobulus testis, 4. Mediastinum testis, 5. Tubuli seminiferi contorti, 6. Tubuli seminiferi recti, 7. Rete testis, 8. Ductuli efferentes testis, 9a. Head of epididymis, 9b. Body of epididymis, 9.c Tail of epididymis,10. Vas deferens, 11a. Tunica vaginalis (parietal lamina), 11b. Tunica vaginalis (visceral lamina), and 12. Cavity of tunica vaginalis.
Inside the Human Testes
Diagram illustrates the scrotum with a portion of the covering removed to display the testis.