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Human male reproductive system and adjacent structures
Latin testis
Gray's subject #258 1236
Artery Testicular artery
Vein Testicular vein, Pampiniform plexus
Nerve Spermatic plexus
Lymph Lumbar lymph nodes
Dorlands/Elsevier t_05/12799705

The testicle (from Latin testis, meaning "witness",[1] plural testes) is the male generative gland in animals. This article will concentrate on mammalian testicles unless otherwise noted.

Additional recommended knowledge


Anatomy and physiology


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

Both functions of the testicle, sperm-forming and endocrine, are under control of gonadotropic hormones produced by the anterior pituitary:

External appearance

Male mammals have two testicles, which are often contained within an extension of the abdomen called the scrotum. In mammals with external testicles it is most common for one testis to hang lower than the other. It is estimated that in about 85% of men the lower hanging testicle is the left one[citation needed]. This is due to differences in the vascular anatomical structure on the right and left sides.

In normal adult human males, testicular size ranges from the lower end of around 14 cm³ to the upper end larger than 35 cm³[citation needed]. Measurement in the living adult is done in two basic ways:

  • comparing the testicle with ellipsoids of known sizes (orchidometer).
  • measuring the length, depth and width with a ruler, a pair of calipers or ultrasound imaging.

The volume is then calculated using the formula for the volume of an ellipsoid: 4/3 π × (length/2) × (width/2) × (depth/2).

To some extent, it is possible to change testicular size. Short of direct injury or subjecting them to adverse conditions, e.g., higher temperature than they are normally accustomed to, they can be shrunk by competing against their intrinsic hormonal function through the use of externally administered steroidal hormones. Steroids taken for muscle enhancement often have the undesired side effect of testicular shrinkage. Similarly, stimulation of testicular functions via gonadotropic-like hormones may enlarge their size. Testicles may shrink or atrophy during hormone replacement therapy.

Internal structure


Duct system

  Under a tough membraneous 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 into old-age, produce sperm cells. The sperm travel from 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 (see spermatogenesis). The sperm move into the vas deferens, and are eventually expelled through the urethra and out of the urethral orifice through muscular contractions.

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

Blood supply and lymphatic drainage


  • The paired testicular arteries arise directly from the abdominal aorta and descend through the inguinal canal, while the scrotum and the rest of the external genitalia is supplied by the internal pudendal artery (itself a branch of the internal iliac artery).
  • Lymphatic drainage of the testes follows the testicular arteries back to the paraaortic lymph nodes, while lymph from the scrotum drains to the inguinal lymph nodes.




The blood-testis barrier


The function of the blood-testis barrier (red highlight in diagram above) may be to prevent an auto-immune reaction. Mature sperm (and their antigens) arise long after immune tolerance is established in infancy. Therefore, since sperm are antigenically different from self tissue, a male animal can react immunologically to his own sperm. In fact, he is capable of making antibodies against them.

Injection of sperm antigens causes inflammation of the testis (autoimmune orchitis) and reduced fertility. Thus, the blood-testis barrier may reduce the likelihood that sperm proteins will induce an immune response, reducing fertility and so progeny.

Temperature regulation

The testes work best at temperatures slightly less than core body temperature (37 °C or 98.6 °F for humans). The spermatogenesis is less efficient at lower and higher temperatures. There are a number of mechanisms to maintain the testes at the optimum temperature.

Cremasteric muscle

The cremasteric muscle is part of the spermatic cord. When this muscle contracts, the cord is shortened and the testicle is moved closer up toward the body, which provides slightly more warmth to maintain optimal testicular temperature. When cooling is required, the cremasteric muscle relaxes and the testicle is lowered away from the warm body and is able to cool. This phenomenon is known as the cremasteric reflex. It also occurs in response to stress (the testicles rise up toward the body in an effort to protect them in a fight), and there are persistent reports that relaxation indicates approach of orgasm. There is a noticeable tendency to also retract during orgasm.

The testicles can also be lifted voluntarily using the pubococcygeus muscle, which partially activates related muscles. This can sometimes be triggered by tightening or sucking in the stomach or abdomen.


There are two phases in which the testicles grow substantially, namely in embryonic and pubertal age.




The testicles grow in response to the start of spermatogenesis. Size depends on lytic function, sperm production (amount of spermatogenisis present in testis), interstitial fluid, and Sertoli cell fluid production. After puberty, the volume of the testicles can be increased by over 500% as compared to the pre-pubertal size.[citation needed] In humans the average testicle size after puberty measures up to be 2 inches long, 0.8 inch in breadth, and 1.2 inches in diameter (5 x 2 x 3 cm).


External testicles






However, the question remains why birds despite having very high core body temperatures have internal testes and did not evolve external testes.[4] It was once theorized that birds used their air sacs to cool the testes internally, but later studies revealed that birds' testes are able to function at core body temperature.[4]



Testicular size


Health issues

The testicles are well-known to be very sensitive to impact and injury. Blue balls is a slang term for a temporary fluid congestion in the testicles and prostate region caused by prolonged sexual arousal.

The most prominent diseases of testicles are:

The removal of one or both testicles is termed:

  • orchidectomy, in medicine (where orchiectomy and orchectomy are synonymous), and
  • castration in general use, especially when done as punishment or torture, or as a catch-all term for orchidectomy in a veterinary context.
  • Gelding in the specifically equine sense.

Testicular prostheses are available to mimic the appearance and feel of one or both testicles, when absent as from injury or as treatment for gender identity disorder. There have also been some instances of their implanting in dogs.

Consumption of testicles

See animelles.

Additional images


  1. ^ [1]
  3. ^ [2]
  4. ^ a b BIOLOGY OF REPRODUCTION 56, 1570-1575 (1997)- Determination of Testis Temperature Rhythms and Effects of Constant Light on Testicular Function in the Domestic Fowl (Gallus domesticus)
  5. ^ [3]
  6. ^ - bumpy-lifestyle-led-to-external-testes
  7. ^ [4]

See also

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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Testicle". A list of authors is available in Wikipedia.