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{{Infobox Anatomy |
Name = Testicle |
Latin = testis |
GraySubject = 258 |
GrayPage = 1236 |
Image = Male_anatomy.png |
Caption = Human male reproductive system and adjacent structures |
Image2 = |
Caption2 = |
Width = 350 |
System = |
Artery = ] |
Vein = ], ] |
Nerve = ] |
Lymph = ] |
MeshName = |
MeshNumber = |
DorlandsPre = t_05 |
DorlandsSuf = 12799705 |
}}{{wiktionary|testes}}
The '''testicle''' (from ] ''testis'', meaning "witness",<ref></ref> ] ''testes'') is the male ] in ]s. This article will concentrate on mammalian testicles unless otherwise noted.


==Anatomy and physiology==
===Function===


Like the ] (to which they are ]), testicles are components of both the ] (being ]s) and the ] (being ]). The respective functions of the testicles are;


*producing ] (spermatozoa)
*producing male ] ]s that of which ] is the best-known
Both functions of the testicle, sperm-forming and endocrine, are under control of gonadotropic hormones produced by the anterior ]:


*] (LH)
*] (FSH)


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===External appearance===
], containing the testicles.]]
Male ]s have two testicles, which are often contained within an extension of the ] called the ]. 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{{Fact|date=January 2008}}. 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 39 cm³{{Fact|date=January 2008}}. Measurement in the living adult is done in two basic ways:


*comparing the testicle with ] of known sizes (]).
*measuring the length, depth and width with a ruler, a pair of calipers or ] imaging.


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The volume is then calculated using the formula for the volume of an ]: 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 ] may enlarge their size. Testicles may shrink or atrophy during ].

===Internal structure===
]

====Duct system====
], 2 ], 3 ], 4 ], 5 ], 6 ], 7 ]s, 8 ]]]
Under a tough membraneous shell, the ], the testis contains very fine coiled tubes called the ]. The tubes are lined with a layer of cells that, from ] into old-age, produce sperm cells.
The sperm travel from the seminiferous tubules to the ] located in the ], to the ], and then to the ] where newly-created sperm cells mature (see ]). The sperm move into the ], and are eventually expelled through the ] and out of the ] through muscular contractions.

Between the seminiferous tubules are special cells called ]s (or "interstitial cells") where ] and other ]s are formed.

====Blood supply and lymphatic drainage====
Blood supply and ] of the testes and scrotum are distinct:
*The paired ] arise directly from the ] and descend through the ], while the scrotum and the rest of the external genitalia is supplied by the ] (itself a branch of the ]).
*Lymphatic drainage of the testes follows the testicular arteries back to the ], while lymph from the scrotum drains to the ].

====Layers====
Many anatomical features of the adult testis reflect its developmental origin in the ].

The layers of tissue enclosing each testicle are derived from the layers of the anterior ]. Notably, the ] arises from the ].

====The blood-testis barrier====
Large molecules cannot pass from the blood into the lumen of a seminiferous tubule due to the presence of ] between adjacent ]. The spermatogonia are in the basal compartment (deep to the level of the tight junctions) and the more mature forms such as primary and secondary spermatocytes and spermatids are in the adluminal compartment.

The function of the ] (red highlight in diagram above) may be to prevent an ] reaction. Mature sperm (and their ]s) 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 (36.6&nbsp;] or 98.6&nbsp;] for humans). The ] 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 ] is part of the ]. 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 ]. 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 ] muscle, which partially activates related muscles. This can sometimes be triggered by tightening or sucking in the stomach or abdomen.

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

===Embryonic===
During mammalian development, the gonads are at first capable of becoming either ] or testes.<ref>Online textbook: "" 6th ed. By Scott F. Gilbert (2000) published by Sinauer Associates, Inc. of Sunderland (MA).</ref> In humans, starting at about week 4 the gonadal rudiments are present within the ] adjacent to the developing kidneys. At about week 6, ] develop within the forming testes. These are comprised of early Sertoli cells that surround and nurture the ]s that migrate into the gonads shortly before sex determination begins. In males, the sex-specific gene ] that is found on the Y-chromosome initiates sex determination by downstream regulation of sex-determining factors, (such as GATA4, SOX9 and AMH), which leads to development of the male phenotype, including directing development of the early bipotential gonad down the male path of development.

===Pubertal===
The testicles grow in response to the start of ]. Size depends on lytic function, sperm production (amount of spermatogenisis present in testis), ], and ] fluid production. After puberty, the volume of the testicles can be increased by over 500% as compared to the pre-pubertal size.{{Fact|date=February 2007}} In humans the average testicle size after puberty measures up to around 2 inches long, 0.8 inch in breadth, and 1.2 inches in diameter (5 x 2 x 3 cm).

==Evolution==
===External testicles===
The basal condition for mammals is to have internal testicles. Only the ]n land mammals, the large group of mammals that includes humans, have externalized testicles. Indeed their testicles function best at temperatures lower than their core body temperature. Their testes are located outside of the body, suspended by the spermatic cord within the scrotum. The testes of the non-boreotherian mammals such as the monotremes, armadillos, sloths, elephants remain within the abdomen.<ref></ref> There are also some Boreoeutherian mammals with internal testes, such as the rhinoceros.

Marine boreotherian mammals such as whales and dolphins, also have internal testes, but it has recently been shown (e.g., for dolphins) that they use elaborate vascular networks to provide the necessary temperature lowering for optimum function. As external testes would increase drag, many boreotherian aquatic mammals have internal testes which are kept cool by special circulatory systems that cool the arterial blood going to the testes by placing the arteries near veins bringing cooled venous blood from the skin.

There are several hypotheses why most boreotherian mammals have external testes which operate best at a temperature that is slightly less than the core body temperature, e.g. that it is stuck with enzymes evolved in a colder temperature due to external testes evolving for different reasons, that the lower temperature of the testes simply is more efficient for sperm production.

'''1) More efficient.''' The classic hypothesis is that cooler temperature of the testes allows for more efficient fertile ]. In other words, there are no possible enzymes operating at normal core body temperature that are as efficient as the ones evolved, at least none appearing in our evolution so far.

The early mammals had lower body temperatures and thus their testes worked efficiently within their body. However it is argued that boreotherian mammals have higher body temperatures than the other mammals and had to develop external testicles to keep them cool. It is argued that those mammals with internal testicles, such as the monotremes, armadillos, sloths, elephants, and rhinoceroses, have a lower core body temperatures than those mammals with external testicles.

However, the question remains why birds despite having very high core body temperatures have internal testes and did not evolve external testes.<ref name =bio>http://www.biolreprod.org/cgi/reprint/56/6/1570.pdf 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)</ref> It was once theorized that birds used their ]s to cool the testes internally, but later studies revealed that birds' testes are able to function at core body temperature.<ref name=bio/>

'''2) Irreversible adaptation to sperm competition'''. It has been suggested that the ancestor of the boreoeutherian mammals was a small mammal that required very large testes (perhaps rather like those of a ]) for ] and thus had to place its testes outside the body.<ref></ref> This led to enzymes involved in spermatogenesis, spermatogenic DNA polymerase beta and recombinase activities evolving a unique temperature optimum, slightly less than core body temperature. When the boreoeutherian mammals then diversified into forms that were larger and/or did not require intense sperm competition they were stuck with enzymes that operated best at cooler temperatures and had to keep their testicles outside the body. This position is made less parsimonious by the fact that the ], a non-boreoeutherian mammal, has external testicles. The ancestors of kangaroos might, separately from boreotherian mammals, have also been subject to heavy sperm competition and thus developed external testes, however, kangaroo external testicles are suggestive of a possible adaptive function for external testes in large animals.

'''3) Protection from abdominal cavity pressure changes.''' One argument for the evolution of external testes is that it protects the testes from abdominal cavity pressure changes caused by jumping and galloping.<ref></ref>

===Testicular size===
Testicular size as a proportion of body weight varies widely. In the mammalian kingdom, there is a tendency for testicular size to correspond with multiple mates (e.g., harems, ]). Production of testicular output sperm and spermatic fluid is also larger in ] animals, possibly a ] for survival. The testicles of the ] are likely to be the largest of any animal, each weighing around 500 kg (1,100 lb).
<!--==Non-mammalian testes==-->

==Health issues==
The testicles are well-known to be very sensitive to ]. ] is a slang term for a temporary fluid congestion in the ] and ] region caused by prolonged ].

The most prominent diseases of testicles are:

*] and other ]
*swelling of a testicle, caused by ]
*inflammation of the testicles, called ]
*inflammation of the epididymis, called ]
*retention cyst of a tubule of the ] or the head of the ], called ]
*] also called ]
*] &mdash; swollen vein from the testes, usually affecting the left testicle<ref></ref>
*anorchidism is the absence of one or both testicles.

The removal of one or both testicles is termed:

*], in medicine (where ''orchiectomy'' and ''orchectomy'' are synonymous), and
*] in general use, especially when done as punishment or torture, or as a catch-all term for ] in a ] context.
*] 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 ]. There have also been some instances of their implanting in dogs.

Other testicular issues:

*] or "undescended testicles", when the testicle does not descend into the scrotum of the infant boy.
*], when the testicle occasionally moves up into the lower ] as the ] contracts. <ref>http://embarrassingproblems.co.uk/problems/problempage040505.htm</ref>

==Consumption of testicles==
See ].

==Additional images==
<gallery>
Image:Testicle-cat.jpg|Testicle of a cat:
1: Extremitas capitata, 2: Extremitas caudata, 3: Margo epididymalis, 4: Margo liber, 5: Mesorchium, 6: Epididymis, 7: testicular artery and vene, 8: Ductus deferens
Image:Illu testis surface.jpg|Testis surface
Image:Illu testis cross section.jpg|Testis cross section
Image:Gray1148.png|The right testis, exposed by laying open the tunica vaginalis.
</gallery>

==References==
{{reflist}}

==See also==
{{sisterlinks}}
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*] (cryptorchismus)
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*] &mdash; the ] list of synonyms and slang words for testicles in many languages
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{{Male reproductive system}}
{{endocrine_system}}

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Revision as of 01:00, 19 March 2008

its the rizzo, the jizzo, the old dirty bastard, inspector dec, rakwan, and of course the method man. BIG GAY HAIRY SLUTTY BALLS!!!



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