Testicle

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Testicle
Figure 28 01 03.JPG
Diagram of inner structures of a human testicle (the labelling "seminal vesicle lobules" is incorrect and should be "testicular lobules" instead)
Gray1144.png
Diagram of the external features and surrounding structures of the testicles of an adult male
Details
Artery Testicular artery
Vein Testicular vein, Pampiniform plexus
Nerve Spermatic plexus
Lymph Lumbar lymph nodes
Identifiers
Latin testis
MeSH D013737
TA98 A09.3.01.001
TA2 3576
FMA 7210
Anatomical terminology
Animation of the migration of spermatozoa from their origin as germ cells to their exit from the vas deferens. A) Blood vessels; B) Head of epididymis; C) Efferent ductules; D) Seminiferous tubules; E) Parietal lamina of tunica vaginalis; F) Visceral lamina of tunica vaginalis; G) Cavity of tunica vaginalis; H) Tunica albuginea; I) Lobule of testis; J) Tail of epididymis; K) Body of epididymis; L) Mediastinum testis; M) Vas deferens. Testis.gif
Animation of the migration of spermatozoa from their origin as germ cells to their exit from the vas deferens. A) Blood vessels; B) Head of epididymis; C) Efferent ductules; D) Seminiferous tubules; E) Parietal lamina of tunica vaginalis; F) Visceral lamina of tunica vaginalis; G) Cavity of tunica vaginalis; H) Tunica albuginea; I) Lobule of testis; J) Tail of epididymis; K) Body of epididymis; L) Mediastinum testis; M) Vas deferens.

A testicle or testis (pl.: testes) is the male gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testicles are to produce both sperm and androgens, primarily testosterone. Testosterone release is controlled by the anterior pituitary luteinizing hormone, whereas sperm production is controlled both by the anterior pituitary follicle-stimulating hormone and gonadal testosterone.

Contents

Structure

Appearance

Male gonad (testes, left) and female gonad (ovaries, right) Male and female gonads 1.png
Male gonad (testes, left) and female gonad (ovaries, right)

Males have two testicles of similar size contained within the scrotum, which is an extension of the abdominal wall. [1] Scrotal asymmetry, in which one testicle extends farther down into the scrotum than the other, is common. This is because of the differences in the vasculature's anatomy. [1] For 85% of men, the right testis hangs lower than the left one. [1]

Measurement and volume

The volume of the testicle can be estimated by palpating it and comparing it to ellipsoids (an orchidometer) of known sizes. Another method is to use calipers, a ruler, or an ultrasound image to obtain the three measurements of the x, y, and z axes (length, depth and width). These measurements can then be used to calculate the volume, using the formula for the volume of an ellipsoid:

However, the most accurate calculation of actual testicular volume is gained from the formula: [2]

An average adult testicle measures up to 5 cm × 2 cm × 3 cm (2 in × 3⁄4 in × 1+1⁄4 in). The Tanner scale, which is used to assess the maturity of the male genitalia, assigns a maturity stage to the calculated volume ranging from stage I, a volume of less than 1.5 cm3; to stage V, a volume greater than 20 cm3. Normal volume is 15 to 25 cm3; the average is 18 cm3 per testis (range 12–30 cm3). [1]

The number of spermatozoa an adult human male produces is directly proportional to testicular volume, as larger testicles contain more seminiferous tubules and Sertoli cells as a result. [3] As such, men with larger testicles produce on average more sperm cells in each ejaculate, as testicular volume is positively correlated with semen profiles. [4]

Internal structure

Transverse section through the left side of the scrotum and the left testis Transversetestis.png
Transverse section through the left side of the scrotum and the left testis

Duct system

The testes are covered by a tough fibrous shell called the tunica albuginea. [5] Under the tunica albuginea, the testes contain very fine-coiled tubes called seminiferous tubules. [5] The tubules are lined with a layer of cells (germ cells) that develop from puberty through old age into sperm cells (also known as spermatozoa or male gametes). [5] The developing sperm travel 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 (spermatogenesis). [6] The sperm move into the vas deferens, and are eventually expelled through the urethra and out of the urethral orifice through muscular contractions. [6]

Primary cell types

Within the seminiferous tubules, the germ cells develop into spermatogonia, spermatocytes, spermatids and spermatozoa through the process of spermatogenesis. The gametes contain DNA for fertilization of an ovum [7] Sertoli cells –the true epithelium of the seminiferous epithelium, critical for the support of germ cell development into spermatozoa. Sertoli cells secrete inhibin. [8] Peritubular myoid cells surround the seminiferous tubules. [9]

Between tubules (interstitial cells) exist Leydig cells [10]  –cells localized between seminiferous tubules that produce and secrete testosterone and other androgens important for puberty (including secondary sexual characteristics like facial hair), sexual behavior, and libido. Sertoli cells support spermatogenesis. [11] Testosterone controls testicular volume.

Immature Leydig cells and interstitial macrophages and epithelial cells are also present.

Blood supply and lymphatic drainage

The testis has three sources of arterial blood supply: the testicular artery, the cremasteric artery, and the artery to the ductus deferens. [12] Blood supply and lymphatic drainage of the testes and scrotum are distinct:

Layers

3D anatomy of the layers surrounding the testis

Many anatomical features of the adult testis reflect its developmental origin in the abdomen. The layers of tissue enclosing each testicle are derived from the layers of the anterior abdominal wall. [1] The cremasteric muscle arises from the internal oblique muscle. [1] [18]

The blood–testis barrier

Large molecules cannot pass from the blood into the lumen of a seminiferous tubule due to the presence of tight junctions between adjacent Sertoli cells. [13] The spermatogonia occupy the basal compartment (deep to the level of the tight junctions) and the more mature forms, such as primary and secondary spermatocytes and spermatids, occupy the adluminal compartment. [13]

The function of the blood–testis barrier may be to prevent an auto-immune reaction. [13] Mature sperm (and their antigens) emerge significantly after immune tolerance is set in infancy. [13] Since sperm are antigenically different from self-tissue, a male animal can react immunologically to his own sperm. The male can make antibodies against them. [13]

Injection of sperm antigens causes inflammation of the testis (auto-immune orchitis) and reduced fertility. [13] The blood–testis barrier may reduce the likelihood that sperm proteins will induce an immune response. [19]

Temperature regulation and responses

Carl Richard Moore in 1926 [20] proposed that testicles were external due to spermatogenesis being enhanced at temperatures slightly less than core body temperature outside the body. The spermatogenesis is less efficient at lower and higher temperatures than 33 °C. Because the testes are located outside the body, the smooth tissue of the scrotum can move them closer or further away from the body. [5] The temperature of the testes is maintained at 34.4 °C, a little below body temperature, as temperatures above 36.7 °C impede spermatogenesis. [1] [5] There are a number of mechanisms to maintain the testes at the optimum temperature. [21]

The cremasteric muscle covers the testicles and the spermatic cord. [22] When this muscle contracts, the cord shortens and the testicles move closer up toward the body, which provides slightly more warmth to maintain optimal testicular temperature. [22] When cooling is required, the cremasteric muscle relaxes and the testicles lower away from the warm body and are able to cool. [22] Contraction also occurs in response to physical stress, such as blunt trauma; the testicles withdraw and the scrotum shrinks very close to the body in an effort to protect them. [23]

The cremasteric reflex will reflexively raise the testicles. The testicles can also be lifted voluntarily using the pubococcygeus muscle, which partially activates related muscles.

Gene and protein expression

The human genome includes approximately 20,000 protein coding genes: 80% of these genes are expressed in adult testes. [24] The testes have the highest fraction of tissue type-specific genes compared to other organs and tissues. [25] About 1000 of them are highly specific for the testes, [24] and about 2,200 show an elevated pattern of expression. A majority of these genes encode for proteins that are expressed in the seminiferous tubules and have functions related to spermatogenesis. [25] Sperm cells express proteins that result in the development of flagella; these same proteins are expressed in the female in cells lining the fallopian tube and cause the development of cilia. Sperm cell flagella and fallopian tube cilia are homologous structures. The testis-specific proteins that show the highest level of expression are protamines. [26]

Development

There are two phases in which the testes grow substantially. These are the embryonic and pubertal phases. During mammalian development, the gonads are at first capable of becoming either ovaries or testes. [27] In humans, starting at about week 4, the gonadal rudiments are present within the intermediate mesoderm adjacent to the developing kidneys. At about week 6, sex cords develop within the forming testes. [1] [28] These are made up of early Sertoli cells that surround and nurture the germ cells that migrate into the gonads shortly before sex determination begins. [1] In males, the sex-specific gene SRY that is found on the Y chromosome initiates sex determination by downstream regulation of sex-determining factors (such as GATA4, SOX9 and AMH), which lead to development of the male phenotype, including directing development of the early bipotential gonad toward the male path of development. [1]

Testes follow the path of descent, from high in the posterior fetal abdomen to the inguinal ring and beyond to the inguinal canal and into the scrotum. [29] In most cases (97% full-term, 70% preterm), both testes have descended by birth. [29] [30] In most other cases, only one testis fails to descend. This is called cryptorchidism. In most cases of cryptorchidism, the issue will mostly resolve itself within the first half year of life. However, if the testes do not descend far enough into the scrotum, surgical anchoring in the scrotum is required due to risks of infertility and testicular cancer. [30]

The testes grow in response to the start of spermatogenesis. Size depends on lytic function, sperm production (amount of spermatogenesis present in testis), interstitial fluid, and Sertoli cell fluid production. The testicles are fully descended before the male reaches puberty.

Clinical significance

Protection and injury

Diseases and conditions

Testicular disease
Specialty Urology, Reproductive medicine

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

Scientists are working on developing lab-grown testicles that might help infertile men in the future. [43]

Effects of exogenous hormones

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 (especially anabolic steroids) often have the undesired side effect of testicular shrinkage.

Stimulation of testicular functions via gonadotropic-like hormones may enlarge their size. Testes may shrink or atrophy during hormone replacement therapy or through chemical castration.

In all cases, the loss in testes volume corresponds with a loss of spermatogenesis.

Society and culture

Depiction of bake-danuki with oversized testicles Yoshitoshi tanuki.jpg
Depiction of bake-danuki with oversized testicles

The testicles of calves, lambs, roosters, turkeys, and other animals are eaten in many parts of the world, often under euphemistic culinary names. Testicles are a by-product of the castration of young animals raised for meat, so they might have been a late-spring seasonal specialty. [44] In modern times, they are generally frozen and available year-round.

In the Middle Ages, men who wanted a boy sometimes had their left testicle removed. This was because people believed that the right testicle made "boy" sperm and the left made "girl" sperm. [45] As early as 330 BC, Aristotle prescribed the ligation (tying off) of the left testicle in men wishing to have boys. [46]

Etymology and slang

One theory about the etymology of the word testis is based on Roman law. The original Latin word testis, "witness", was used in the firmly established legal principle "Testis unus, testis nullus" (one witness [equals] no witness), meaning that testimony by any one person in court was to be disregarded unless corroborated by the testimony of at least another. This led to the common practice of producing two witnesses, bribed to testify the same way in cases of lawsuits with ulterior motives. Since such witnesses always came in pairs, the meaning was accordingly extended, often in the diminutive (testiculus, testiculi).[ citation needed ]

Another theory says that testis is influenced by a loan translation, from Greek parastatēs "defender (in law), supporter" that is "two glands side by side". [47]

There are multiple slang terms for the testes. They may be referred to as "balls". Frequently, "nuts" (sometimes intentionally misspelled as "nutz") are also a slang term for the testes due to the geometric resemblance. One variant of the term includes "Deez Nuts", which was used for a satirical political candidate in 2016.

In Spanish, the term huevos is used, which is Spanish for eggs.

Other animals

External appearance

In seasonal breeders, the weight of the testes often increases during the breeding season. [48] The testicles of a dromedary camel are 7–10 cm (2.8–3.9 in) long, 4.5 cm (1.8 in) deep and 5 cm (2.0 in) in width. The right testicle is often smaller than the left. [49]

In sharks, the testicle on the right side is usually larger. In many bird and mammal species, the left may be larger. Fish usually have two testes of a similar size. The primitive jawless fish have only a single testis, located in the midline of the body, although this forms from the fusion of paired structures in the embryo. [50]

Location

Internal

The basal condition for mammals is to have internal testes. [51] The testes of monotremes, [52] [53] xenarthrans, [53] and afrotherians [54] remain within the abdomen (testicondy). There are also some marsupials with external testes [55] [56] [57] and boreoeutherian mammals with internal testes, such as the rhinoceros. [58] Cetaceans such as whales and dolphins also have internal testes. [59] [60] As external testes would increase drag in the water, they 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. [61] [62] In odobenids and phocids, the location of the testes is para-abdominal, though otariids have scrotal testes. [63]

External

Boreoeutherian land mammals, the large group of mammals that includes humans, have externalized testes. [64] Their testes function best at temperatures lower than their core body temperature. Their testes are located outside of the body and are suspended by the spermatic cord within the scrotum.

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

The classic hypothesis is that cooler temperature of the testes allows for more efficient fertile spermatogenesis. There are no possible enzymes operating at normal core body temperature that are as efficient as the ones evolved.

Early mammals had lower body temperatures and thus their testes worked efficiently within their body. However, boreotherian mammals may have higher body temperatures than the other mammals and had to develop external testes to keep them cool. One argument is that mammals with internal testes, such as the monotremes, armadillos, sloths, elephants, and rhinoceroses, have a lower core body temperatures than those mammals with external testes.[ citation needed ]

Researchers have wondered why birds, despite having very high core body temperatures, have internal testes and did not evolve external testes. [65] 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. [65]

Some mammals with seasonal breeding cycles keep their testes internal until the breeding season. After that, their testes descend and increase in size and become external. [66]

The ancestor of the boreoeutherian mammals may have been a small mammal that required very large testes for sperm competition and thus had to place its testes outside the body. [67] This might have led to enzymes involved in spermatogenesis, spermatogenic DNA polymerase beta and recombinase activities evolving a unique temperature optimum that is slightly less than core body temperature. When the boreoeutherian mammals diversified into forms that were larger or did not require intense sperm competition, they still produced enzymes that operated best at cooler temperatures and had to keep their testes outside the body. This position is made less parsimonious because the kangaroo, a non-boreoeutherian mammal, has external testicles. Separately from boreotherian mammals, the ancestors of kangaroos might have also been subject to heavy sperm competition and thus developed external testes; however, kangaroo external testes are suggestive of a possible adaptive function for external testes in large animals.

One argument for the evolution of external testes is that it protects the testes from abdominal cavity pressure changes caused by jumping and galloping. [68]

Mild, transient scrotal heat stress causes DNA damage, reduced fertility and abnormal embryonic development in mice. [69] DNA strand breaks were found in spermatocytes recovered from testicles subjected to 40 °C or 42 °C for 30 minutes. [69] These findings suggest that the external location of the testicles provides the adaptive benefit of protecting spermatogenic cells from heat-induced DNA damage that could otherwise lead to infertility and germline mutation.

Size

Cross section of rabbit testis, photographed in bright-field microscopy at 40x magnification Rabbit testis.jpg
Cross section of rabbit testis, photographed in bright-field microscopy at 40× magnification

The relative size of the testes is often influenced by mating systems. [70] 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, polygamy). Production of testicular output sperm and spermatic fluid is also larger in polygamous animals, possibly a spermatogenic competition for survival. The testes of the right whale are likely to be the largest of any animal, each weighing around 500 kg (1,100 lb). [71]

Among the Hominidae, gorillas have little female promiscuity and sperm competition and the testes are small compared to body weight (0.03%). Chimpanzees have high promiscuity and large testes compared to body weight (0.3%). Human testicular size falls between these extremes (0.08%). [72]

Testis weight also varies in seasonal breeders like red foxes, [73] golden jackals, [74] and coyotes. [48]

Internal structure

Amphibians and most fish do not possess seminiferous tubules. Instead, the sperm are produced in spherical structures called sperm ampullae. These are seasonal structures, releasing their contents during the breeding season, and then being reabsorbed by the body. Before the next breeding season, new sperm ampullae begin to form and ripen. The ampullae are otherwise essentially identical to the seminiferous tubules in higher vertebrates, including the same range of cell types. [50]

See also

General and cited references

Citations

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<span class="mw-page-title-main">Testicular torsion</span> Medical condition

Testicular torsion occurs when the spermatic cord twists, cutting off the blood supply to the testicle. The most common symptom in children is sudden, severe testicular pain. The testicle may be higher than usual in the scrotum and vomiting may occur. In newborns, pain is often absent and instead the scrotum may become discolored or the testicle may disappear from its usual place.

<span class="mw-page-title-main">Testicular cancer</span> Medical condition

Testicular cancer is cancer that develops in the testicles, a part of the male reproductive system. Symptoms may include a lump in the testicle or swelling or pain in the scrotum. Treatment may result in infertility.

<span class="mw-page-title-main">Epididymis</span> Tube that connects a testicle to a vas deferens

The epididymis is an elongated tubular structure attached to the posterior side of each one of the two male reproductive glands, the testicles. It is a single, narrow, tightly coiled tube in adult humans, 6 to 7 centimetres in length; uncoiled the tube would be approximately 6 m long. It connects the testicle to the vas deferens in the male reproductive system. The epididymis serves as an interconnection between the multiple efferent ducts at the rear of a testicle (proximally), and the vas deferens (distally). Its primary function is the storage, maturation and transport of sperm cells.

<span class="mw-page-title-main">Cryptorchidism</span> Medical condition

Cryptorchidism, also known as undescended testis, is the failure of one or both testes to descend into the scrotum. The word is from Greek κρυπτός 'hidden' and ὄρχις 'testicle'. It is the most common birth defect of the male genital tract. About 3% of full-term and 30% of premature infant boys are born with at least one undescended testis. However, about 80% of cryptorchid testes descend by the first year of life, making the true incidence of cryptorchidism around 1% overall. Cryptorchidism may develop after infancy, sometimes as late as young adulthood, but that is exceptional.

<span class="mw-page-title-main">Cremaster muscle</span> Muscle covering the testicles and spermatic cords

The cremaster muscle is a paired structure made of thin layers of striated and smooth muscle that covers the testicles and the spermatic cords in human males. It consists of the lateral and medial parts. Cremaster is an involuntary muscle, responsible for the cremasteric reflex; a protective and physiologic superficial reflex of the testicles. The reflex raises and lowers the testicles in order to keep them protected. Along with the dartos muscle of the scrotum, it regulates testicular temperature, thus aiding the process of spermatogenesis.

<span class="mw-page-title-main">Spermatogenesis</span> Production of sperm

Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testicle. This process starts with the mitotic division of the stem cells located close to the basement membrane of the tubules. These cells are called spermatogonial stem cells. The mitotic division of these produces two types of cells. Type A cells replenish the stem cells, and type B cells differentiate into primary spermatocytes. The primary spermatocyte divides meiotically into two secondary spermatocytes; each secondary spermatocyte divides into two equal haploid spermatids by Meiosis II. The spermatids are transformed into spermatozoa (sperm) by the process of spermiogenesis. These develop into mature spermatozoa, also known as sperm cells. Thus, the primary spermatocyte gives rise to two cells, the secondary spermatocytes, and the two secondary spermatocytes by their subdivision produce four spermatozoa and four haploid cells.

<span class="mw-page-title-main">Seminiferous tubule</span> Location of meiosis and creation of spermatozoa

Seminiferous tubules are located within the testicles, and are the specific location of meiosis, and the subsequent creation of male gametes, namely spermatozoa.

<span class="mw-page-title-main">Rete testis</span> Tubules that carry sperm

The rete testis is an anastomosing network of delicate tubules located in the hilum of the testicle that carries sperm from the seminiferous tubules to the efferent ducts. It is the homologue of the rete ovarii in females. Its function is to provide a site for fluid reabsorption.

<span class="mw-page-title-main">Male reproductive system</span> Reproductive system of the human male

The male reproductive system consists of a number of sex organs that play a role in the process of human reproduction. These organs are located on the outside of the body, and within the pelvis.

<span class="mw-page-title-main">Blood–testis barrier</span> Physical barrier between the blood vessels and the seminiferous tubules of animal testes

The blood–testis barrier is a physical barrier between the blood vessels and the seminiferous tubules of the animal testes. The name "blood-testis barrier" is misleading as it is not a blood-organ barrier in a strict sense, but is formed between Sertoli cells of the seminiferous tubule and isolates the further developed stages of germ cells from the blood. A more correct term is the Sertoli cell barrier (SCB).

An alternative male contraceptive method involves heating the testicles so that they cannot produce sperm. Sperm are best produced at a temperature slightly below body temperature. The muscles around a male's scrotum involuntarily tighten if the man's body temperature drops, and they loosen, allowing the testes to hang, if the body temperature rises. This is the body's way of keeping the sperm at an ideal temperature. This means that sperm production can be disrupted with increased temperature. Some suggest exposure to high temperatures can affect fertility for months.

<span class="mw-page-title-main">Testicular sperm extraction</span> Surgical procedure

Testicular sperm extraction (TESE) is a surgical procedure in which a small portion of tissue is removed from the testicle and any viable sperm cells from that tissue are extracted for use in further procedures, most commonly intracytoplasmic sperm injection (ICSI) as part of in vitro fertilisation (IVF). TESE is often recommended to patients who cannot produce sperm by ejaculation due to azoospermia.

<span class="mw-page-title-main">Lobules of testis</span>

The lobules of testis are of partitions of the testis formed by septa of testis. The lobules of testis contain the tightly coiled seminiferous tubule. There are some hundreds of lobules in a testicle.

The development of the reproductive system is the part of embryonic growth that results in the sex organs and contributes to sexual differentiation. Due to its large overlap with development of the urinary system, the two systems are typically described together as the genitourinary system.

The development of the gonads is part of the prenatal development of the reproductive system and ultimately forms the testicles in males and the ovaries in females. The immature ova originate from cells from the dorsal endoderm of the yolk sac. Once they have reached the gonadal ridge they are called oogonia. Development proceeds and the oogonia become fully surrounded by a layer of connective tissue cells. In this way, the rudiments of the ovarian follicles are formed.

<span class="mw-page-title-main">Sertoli cell-only syndrome</span> Medical condition

Sertoli cell-only syndrome (SCOS), also known as germ cell aplasia, is defined by azoospermia where the testicular seminiferous tubules are lined solely with sertoli cells. Sertoli cells contribute to the formation of the blood-testis barrier and aid in sperm generation. These cells respond to follicle-stimulating hormone, which is secreted by the hypothalamus and aids in spermatogenesis.

<span class="mw-page-title-main">Scrotum</span> Sac of skin that protects the testicles

In most terrestrial mammals, the scrotum or scrotal sac is a part of the external male genitalia located at the base of the penis. It consists of a sac of skin containing the external spermatic fascia, testicles, epididymides, and vasa deferentia. The scrotum will usually tighten during penile erection and when exposed to cold temperatures.

FNA mapping is an application of fine-needle aspiration (FNA) to the testis for the diagnosis of male infertility. FNA cytology has been used to examine pathological human tissue from various organs for over 100 years. As an alternative to open testicular biopsy for the last 40 years, FNA mapping has helped to characterize states of human male infertility due to defective spermatogenesis. Although recognized as a reliable, and informative technique, testis FNA has not been widely used in U.S. to evaluate male infertility. Recently, however, testicular FNA has gained popularity as both a diagnostic and therapeutic tool for the management of clinical male infertility for several reasons:

  1. The testis is an ideal organ for evaluation by FNA because of its uniform cellularity and easy accessibility.
  2. The trend toward minimally invasive procedures and cost-containment views FNA favorably compared to surgical testis biopsy.
  3. The realization that the specific histologic abnormality observed on testis biopsy has no definite correlation to either the etiology of infertility or to the ability to find sperm for assisted reproduction.
  4. Assisted reproduction has undergone dramatic advances such that testis sperm are routinely used for biological pregnancies, thus fueling the development of novel FNA techniques to both locate and procure sperm.
<span class="mw-page-title-main">Scrotal ultrasound</span> Medical ultrasound examination of the scrotum.

Scrotalultrasound is a medical ultrasound examination of the scrotum. It is used in the evaluation of testicular pain, and can help identify solid masses.

In vitro spermatogenesis is the process of creating male gametes (spermatozoa) outside of the body in a culture system. The process could be useful for fertility preservation, infertility treatment and may further develop the understanding of spermatogenesis at the cellular and molecular level. 

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