Scrotum

The scrotum is an anatomical male reproductive structure that consists of a suspended dual-chambered sack of skin and smooth muscle that is present in most terrestrial male mammals and located under the penis. One testis is typically lower than the other to avoid compression in the event of impact.[1] The perineal raphe is a small, vertical, slightly raised ridge of scrotal skin under which is found the scrotal septum. It appears as a thin longitudinal line that runs front to back over the entire scrotum. The scrotum contains the external spermatic fascia, testes, epididymis, and ductus deferens. It is a distention of the perineum and carries some abdominal tissues into its cavity including the testicular artery, testicular vein, and pampiniform plexus. In humans and some other mammals, the scrotum becomes covered with pubic hair at puberty. The scrotum will usually tighten during penile erection and when exposed to cold temperature.

The scrotum is biologically homologous to the labia majora in females. Although present in most mammals, the external scrotum is absent in streamlined marine mammals, such as whales and seals,[2] as well as in some lineages of land mammals, such as the afrotherians, xenarthrans, and numerous families of bats, rodents, and insectivores.[3][4]

Scrotum
HQ SAM ST2
Human scrotum in a relaxed state (left) and a tense state (right)
Details
PrecursorLabioscrotal folds
ArteryAnterior scrotal artery & Posterior scrotal artery
VeinTesticular vein
NervePosterior scrotal nerves, Anterior scrotal nerves, genital branch of genitofemoral nerve, perineal branches of posterior femoral cutaneous nerve
LymphSuperficial inguinal lymph nodes
Identifiers
LatinScrotum
MeSHD012611
TAA09.4.03.001
FMA18252
Anatomical terminology

Structure

Nerve supply

Nerve Surface[5]
Genital branch of genitofemoral nerve anterolateral
Anterior scrotal nerves (from ilioinguinal nerve) anterior
Posterior scrotal nerves (from perineal nerve) posterior
perineal branches of posterior femoral cutaneous nerve inferior

Blood supply

Gray1143
Diagram of the scrotum. On the left side the cavity of the tunica vaginalis has been opened; on the right side only the layers superficial to the Cremaster muscle have been removed.
Blood vessels[6]
Anterior scrotal artery originates from the deep external pudendal artery[7]
Posterior scrotal artery
Testicular artery

Skin and glands

Skin associated tissues [6]
Pubic hair
Sebaceous glands
Apocrine glands
Smooth muscle

The skin on the scrotum is more highly pigmented compared to the rest of the body. The septum is a connective tissue membrane dividing the scrotum into two cavities. [8]

Lymphatic system

The scrotum lymph drains initially into the superficial inguinal lymph nodes, this then drains into the deep inguinal lymph nodes. The deep inguinal lymph nodes drain into the common iliac which ultimately releases lymph into the cisterna chyli.

Lymphatic vessels[9]
Superficial inguinal lymph nodes
Popliteal lymph nodes

Asymmetry

One testis is typically lower than the other, which is believed to function to avoid compression in the event of impact; in humans, the left testis is typically lower than the right.[1] An alternative view is that testis descent asymmetry evolved to enable more effective cooling of the testicles.[10]

Internal structure

Figure 28 01 02
Image showing musculature and inner workings of the scrotum.

Additional tissues and organs reside inside the scrotum and are described in more detail in the following articles:

Development

Genital homology between sexes

Male sex hormones are secreted by the testes later in embryonic life to cause the development of secondary sex organs. The scrotum is developmentally homologous to the labia minora and labia majora. The raphe does not exist in females. Reproductive organs and tissues develop in females and males begin during the fifth week after fertilization. The gonadal ridge grows behind the peritoneal membrane. By the sixth week, string-like tissues called primary sex cords form within the enlarging gonadal ridge. Externally, a swelling called the genital tubercule appears over the cloacal membrane.

Up until the eighth week after fertilization, the reproductive organs do not appear to be different between the male and female and are called in-differentiated. Testosterone secretion starts during week eight, reaches peak levels during week 13 and eventually declines to very low levels by the end of the second trimester. The testosterone causes the masculinization of the labioscrotal folds into the scrotum. The scrotal raphe is formed when the embryonic, urethral groove closes by week 12.[11]

Scrotal growth and puberty

Though the testes and scrotum form early in embryonic life, sexual maturation begins upon entering puberty. The increased secretion of testosterone causes the darkening of the skin and development of pubic hair on the scrotum.[12]

Function

The scrotum regulates the temperature of the testes and maintains it at 35 degrees Celsius (95 degrees Fahrenheit), i.e. two degrees below the body temperature of 37 degrees Celsius (98.6 degrees Fahrenheit). Higher temperatures affect spermatogenesis[13] Temperature control is accomplished by the smooth muscles of the scrotum moving the testicles either closer to or further away from the abdomen dependent upon the ambient temperature. This is accomplished by the cremaster muscle in the abdomen and the dartos fascia (muscular tissue under the skin).[12]

Having the scrotum and testicles situated outside the abdominal cavity may provide additional advantages. The external scrotum is not affected by abdominal pressure. This may prevent the emptying of the testes before the sperm were matured sufficiently for fertilization.[13] Another advantage is it protects the testes from jolts and compressions associated with an active lifestyle. Animals that move at a steady pace – such as elephants, whales, and marsupial moles – have internal testes and no scrotum.[14] Unlike placental mammals, some male marsupials have a scrotum that is anterior to the penis,[15][16][17] although there are several marsupial species without an external scrotum.[18] In humans, the scrotum may provide some friction during intercourse, helping to enhance the activity.[19]

Clinical significance

A study has indicated that use of a laptop computer positioned on the lap can negatively affect sperm production.[20][21]

Diseases and conditions

The scrotum and its contents can develop diseases or incur injuries. These include:

See also

Bibliography

Books
  • This article incorporates text in the public domain from page 1237 of the 20th edition of Gray's Anatomy (1918)
  • Van De Graaff, Kent M.; Fox, Stuart Ira (1989). Concepts of Human Anatomy and Physiology. Dubuque, Iowa: William C. Brown Publishers. ISBN 978-0697056757.
  • Elson, Lawrence; Kapit, Wynn (1977). The Anatomy Coloring. New York, New York: Harper & Row. ISBN 978-0064539142.
  • "Gross Anatomy Image". Medical Gross Anatomy Atlas Images. University of Michigan Medical School. 1997. Retrieved 2015-02-23.
  • Berkow, MD, editor, Robert (1977). The Merck Manual of Medical Information; Home Edition. Whitehouse Station, New Jersey: Merck Research Laboratories. ISBN 978-0911910872.CS1 maint: Multiple names: authors list (link) CS1 maint: Extra text: authors list (link)

References

  1. ^ a b Anthony F.Bogaert, "Genital asymmetry in men Archived 2015-05-28 at the Wayback Machine", Human Reproduction vol.12 no.1 pp.68–72, 1997. PMID 9043905.
  2. ^ William F. Perrin; Bernd Würsig; J.G.M. Thewissen (26 February 2009). Encyclopedia of Marine Mammals. Academic Press. ISBN 978-0-08-091993-5.
  3. ^ "Scrotum". National Institutes of Health. Retrieved 6 January 2011.
  4. ^ Lovegrove, B. G. (2014). "Cool sperm: Why some placental mammals have a scrotum". Journal of Evolutionary Biology. 27 (5): 801–814. doi:10.1111/jeb.12373. PMID 24735476.
  5. ^ Moore, Keith; Anne Agur (2007). Essential Clinical Anatomy, Third Edition. Lippincott Williams & Wilkins. p. 132. ISBN 978-0-7817-6274-8.
  6. ^ a b Elson 1977.
  7. ^ antthigh at The Anatomy Lesson by Wesley Norman (Georgetown University)
  8. ^ "Scrotum". Encyclopædia Britannica. Retrieved 2015-02-24.
  9. ^ "VIII. The Lymphatic System. 5. The Lymphatics of the Lower Extremity. Gray, Henry. 1918. Anatomy of the Human Body". Retrieved 2015-02-24.
  10. ^ Gallup, Gordon G.; Finn, Mary M.; Sammis, Becky (2009). "On the Origin of Descended Scrotal Testicles: The Activation Hypothesis". Evolutionary Psychology. 7 (4): 147470490900700. doi:10.1177/147470490900700402.
  11. ^ Van de Graaff 1989, p. 927-931.
  12. ^ a b Van de Graaff 1989, p. 935.
  13. ^ a b Van de Graaff 1989, p. 936.
  14. ^ "Science : Bumpy lifestyle led to external testes - 17 August 1996 - New Scientist". New Scientist. Retrieved 2007-11-06.
  15. ^ Hugh Tyndale-Biscoe; Marilyn Renfree (30 January 1987). Reproductive Physiology of Marsupials. Cambridge University Press. ISBN 978-0-521-33792-2.
  16. ^ Libbie Henrietta Hyman (15 September 1992). Hyman's Comparative Vertebrate Anatomy. University of Chicago Press. pp. 583–. ISBN 978-0-226-87013-7.
  17. ^ Menna Jones; Chris R. Dickman; Michael Archer (2003). Predators with Pouches: The Biology of Carnivorous Marsupials. Csiro Publishing. ISBN 978-0-643-06634-2.
  18. ^ C. Hugh Tyndale-Biscoe (2005). Life of Marsupials. Csiro Publishing. ISBN 978-0-643-06257-3.
  19. ^ Jones, Richard (2013). Human Reproductive Biology. Academic Press. p. 74. ISBN 9780123821850. The rear-entry position of mating may allow the scrotum to stimulate the clitoris and, in this way, may produce an orgasm ...
  20. ^ "Laptops may damage male fertility". BBC News. 2004-12-09. Retrieved 2012-01-30.
  21. ^ Sheynkin, Yefim; et al. (February 2005). "Increase in scrotal temperature in laptop computer users". Hum. Reprod. 20 (2): 452–455. doi:10.1093/humrep/deh616. PMID 15591087.
  22. ^ "Paget's disease of the scrotum Symptoms, Diagnosis, Treatments and Causes". RightDiagnosis.com. Retrieved 2015-02-24.
  23. ^ "Common scrotal skin diseases". TCMWell. Retrieved 2015-02-24.
  24. ^ a b TCMwell.
Aarskog–Scott syndrome

Aarskog–Scott syndrome is a rare disease inherited as X-linked and characterized by short stature, facial abnormalities, skeletal and genital anomalies. This condition mainly affects males, although females may have mild features of the syndrome.

Angiokeratoma

Angiokeratoma is a benign cutaneous lesion of capillaries, resulting in small marks of red to blue color and characterized by hyperkeratosis. Angiokeratoma corporis diffusum refers to Fabry's disease, but this is usually considered a distinct condition.

Bull

A bull is an intact (i.e., not castrated) adult male of the species Bos taurus (cattle). More muscular and aggressive than the female of the species, the cow, the bull has long been an important symbol in many cultures, and plays a significant role in both beef ranching and dairy farming, and in a variety of other cultural activities.

Chimney sweeps' carcinoma

Chimney sweep's cancer, also called soot wart, is a squamous cell carcinoma of the skin of the scrotum. It has the distinction of being the first reported form of occupational cancer, and was initially identified by Percivall Pott in 1775. It was initially noticed as being prevalent amongst chimney sweeps.

Cock ring

A cock ring or cockring is a ring worn around the penis, usually at the base. The primary purpose of wearing a cock ring is to restrict the flow of blood from the erect penis in order to produce a stronger erection or to maintain an erection for a longer period of time. Genital adornment is another purpose, as is repositioning the genitals to provide an enhanced appearance.

Cock rings are also called C rings, penis rings or shaft rings. When used in cases of erectile dysfunction (ED), they are known by various other names, such as erection rings and tension rings.

Cock rings worn just behind the corona of the glans of the penis are known as glans rings, head rings or cock crowns.

A ring that is worn around the penis and scrotum is also usually called a cock ring, but is sometimes referred to as a cock and ball ring.

Rings that are worn just round the scrotum, in order to hold the testicles, are usually called testicle cuffs or ball stretchers.

Cremaster muscle

The cremaster muscle is a muscle that covers the testis and the spermatic cord.

Cryptorchidism

Cryptorchidism is the absence of one or both testes from the scrotum. The word is from the Greek κρυπτός, kryptos, meaning hidden, and ὄρχις, orchis, meaning 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 (the majority within three months), making the true incidence of cryptorchidism around 1% overall. Cryptorchidism may develop after infancy, sometimes as late as young adulthood, but that is exceptional.

Cryptorchidism is distinct from monorchism, the condition of having only one testicle. Though the condition may occur on one or both sides, it more commonly affects the right testis.A testis absent from the normal scrotal position may be:

Anywhere along the "path of descent" from high in the posterior (retroperitoneal) abdomen, just below the kidney, to the inguinal ring

In the inguinal canal

Ectopic, having "wandered" from the path of descent, usually outside the inguinal canal and sometimes even under the skin of the thigh, the perineum, the opposite scrotum, or the femoral canal

Undeveloped (hypoplastic) or severely abnormal (dysgenetic)

Missing (also see anorchia).About two-thirds of cases without other abnormalities are unilateral; most of the other third involve both testes. In 90% of cases, an undescended testis can be felt in the inguinal canal. In a small minority of cases, missing testes may be found in the abdomen or appear to be nonexistent (truly "hidden").

Undescended testes are associated with reduced fertility, increased risk of testicular germ-cell tumors, and psychological problems when the boy is grown. Undescended testes are also more susceptible to testicular torsion (and subsequent infarction) and inguinal hernias. Without intervention, an undescended testicle will usually descend during the first year of life, but to reduce these risks, undescended testes can be brought into the scrotum in infancy by a surgical procedure called an orchiopexy.Although cryptorchidism nearly always refers to congenital absence or maldescent, a testis observed in the scrotum in early infancy can occasionally "reascend" (move back up) into the inguinal canal. A testis which can readily move or be moved between the scrotum and canal is referred to as retractile.

Cryptorchidism, hypospadias, testicular cancer, and poor semen quality make up the syndrome known as testicular dysgenesis syndrome.

Dartos

The dartos fascia or simply dartos is a layer of connective tissue found in the penile shaft, foreskin, and scrotum. The penile portion is referred to as the superficial fascia of penis or the subcutaneous tissue of penis, while the scrotal part is the dartos proper. In addition to being continuous with itself between the scrotum and the penis, it is also continuous with Colles fascia of the perineum and Scarpa's fascia of the abdomen.It lies just below the skin, which places it just superficial to the external spermatic fascia in the scrotum and to Buck's fascia in the penile shaft.

In the scrotum, it consists mostly of smooth muscle. The tone of this smooth muscle is responsible for the wrinkled (rugose) appearance of the scrotum.In females, the same muscle fibers are less well developed and termed dartos muliebris, lying beneath the skin of the labia majora.

It receives innervation from postganglionic sympathetic nerve fibers arriving via the ilioinguinal nerve and the posterior scrotal nerve.

Epididymis

The epididymis (; plural: epididymides or ) is a tube that connects a testicle to a vas deferens in the male reproductive system. It is present in all male reptiles, birds, and mammals. It is a single, narrow, tightly-coiled tube in adult humans, 6 to 7 meters (20 to 23 ft) in length connecting the efferent ducts from the rear of each testicle to its vas deferens.

Fordyce spots

Fordyce spots (also termed Fordyce granules) are visible sebaceous glands that are present in most individuals. They appear on the genitals and/or on the face and in the mouth. They appear as small, painless, raised, pale, red or white spots or bumps 1 to 3 mm in diameter that may appear on the scrotum, shaft of the penis or on the labia, as well as the inner surface (retromolar mucosa) and vermilion border of the lips of the face. They are not associated with any disease or illness, nor are they infectious but rather they represent a natural occurrence on the body. No treatment is therefore required, unless the individual has cosmetic concerns. Persons with this condition sometimes consult a dermatologist because they are worried they may have a sexually transmitted disease (especially genital warts) or some form of cancer.

Hafada piercing

A hafada piercing is a surface piercing anywhere on the skin of the scrotum. This piercing does not penetrate deep into the scrotum, and due to the looseness and flexibility of the skin in that area, does not migrate or reject as much as many other surface piercings. A piercing that passes through the scrotum, from front-to-back, or from side-to-side, is known as a transscrotal piercing. Multiple hafada piercings are not uncommon as an extension of a frenum ladder.

Inguinal hernia

An inguinal hernia is a protrusion of abdominal-cavity contents through the inguinal canal. Symptoms are present in about 66% of affected people. This may include pain or discomfort especially with coughing, exercise, or bowel movements. Often it gets worse throughout the day and improves when lying down. A bulging area may occur that becomes larger when bearing down. Inguinal hernias occur more often on the right than left side. The main concern is strangulation, where the blood supply to part of the intestine is blocked. This usually produces severe pain and tenderness of the area.Risk factors for the development of a hernia include: smoking, chronic obstructive pulmonary disease, obesity, pregnancy, peritoneal dialysis, collagen vascular disease, and previous open appendectomy, among others. Hernias are partly genetic and occur more often in certain families. It is unclear if inguinal hernias are associated with heavy lifting. Hernias can often be diagnosed based on signs and symptoms. Occasionally medical imaging is used to confirm the diagnosis or rule out other possible causes.Groin hernias that do not cause symptoms in males do not need to be repaired. Repair, however, is generally recommended in females due to the higher rate of femoral hernias which have more complications. If strangulation occurs immediate surgery is required. Repair may be done by open surgery or by laparoscopic surgery. Open surgery has the benefit of possibly being done under local anesthesia rather than general anesthesia. Laparoscopic surgery generally has less pain following the procedure.In 2015 inguinal, femoral and abdominal hernias affected about 18.5 million people. About 27% of males and 3% of females develop a groin hernia at some time in their life. Groin hernias occur most often before the age of one and after the age of fifty. Globally, inguinal, femoral and abdominal hernias resulted in 60,000 deaths in 2015 and 55,000 in 1990.

Labia majora

The labia majora (singular: labium majus) are two prominent longitudinal cutaneous folds that extend downward and backward from the mons pubis to the perineum. Together with the labia minora they form the labia of the vulva.

The labia majora are homologous to the male scrotum.

Marsupial

Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia and the Americas. A distinctive characteristic common to these species is that most of the young are carried in a pouch. Well-known marsupials include kangaroos, wallabies, koalas, possums, opossums, wombats, and Tasmanian devils. Some lesser-known marsupials are the dunnarts, potoroos and cuscuses.

Marsupials represent the clade originating from the last common ancestor of extant metatherians. Like other mammals in the Metatheria, they give birth to relatively undeveloped young that often reside in a pouch located on their mothers’ abdomen for a certain amount of time. Close to 70% of the 334 extant species occur on the Australian continent (the mainland, Tasmania, New Guinea and nearby islands). The remaining 100 are found in the Americas — primarily in South America, but thirteen in Central America, and one in North America, north of Mexico.

The word marsupial comes from marsupium, the technical term for the abdominal pouch. It, in turn, is borrowed from Latin and ultimately from the ancient Greek μάρσιππος mársippos, meaning "pouch".

Mule spinners' cancer

Mule spinners' cancer or mule-spinners' cancer was a cancer, an epithelioma of the scrotum. It was first reported in 1887 in a cotton mule spinner. In 1926, a British Home Office committee strongly favoured the view that this form of cancer was caused by the prolonged action of mineral oils on the skin of the scrotum, and of these oils, shale oil was deemed to be the most carcinogenic. From 1911 to 1938, there were 500 deaths amongst cotton mule-spinners from cancer of the scrotum, but only three amongst wool mule spinners.

Perineal raphe

The perineal raphe is a visible line or ridge of tissue on the human body that extends from the anus through the perineum. It is found in both males and females, and arises from the fusion of the urogenital folds.

In males, this structure continues through the midline of the scrotum (scrotal raphe) and upwards through the posterior midline aspect of the penis (penile raphe). It also exists deeper through the scrotum where it is called the scrotal septum. It is the result of a fetal developmental phenomenon whereby the scrotum and penis close toward the midline and fuse.It has been argued that the "rib" in the biblical story of Adam and Eve is actually a mistranslation of a Biblical Hebrew euphemism for baculum (penis bone), and that its removal from Adam in the Book of Genesis is a creation narrative to explain its absence in humans, as well as the presence of the raphe– as a resultant 'scar'.

Teabagging

Teabagging is a slang term for the sexual act of a man placing his scrotum in the mouth of his sexual partner for pleasure, or onto the face or head of another person, sometimes as a comedic device.

The name of the practice, when it is done in a repeated in-and-out motion, is derived from its passing resemblance to the dipping of a tea bag into a cup of hot water as a method of brewing tea. As a form of non-penetrative sex, it can be done for its own enjoyment or as foreplay. The practice may also be performed during sexual assault. This practice was made popular in the 1990s video game Counter-Strike, in which one player would repeatedly crouch over the opponent's dead body.

Testicle

Testicle or testis is the male reproductive gland or gonad in all animals, including humans. It is homologous to the female ovary. The functions of the testes 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.

Varicocele

A varicocele is an abnormal enlargement of the pampiniform venous plexus in the scrotum. This plexus of veins drains blood from the testicles back to the heart. The vessels originate in the abdomen and course down through the inguinal canal as part of the spermatic cord on their way to the testis. Varicoceles occur in around 15% to 20% of all men. The incidence of varicocele increase with age.

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