Scrotum

anatomical male reproductive structure that consists of a suspended sack of skin
For the obsolete dinosaur fossil name, see Megalosaurus § "Scrotum humanum".
Scrotum
HQ SAM ST2.jpg
Human scrotum in a relaxed state (left) and a tense state (right)
Details
Precursor Labioscrotal folds
Artery Anterior scrotal artery & Posterior scrotal artery
Vein Testicular vein
Nerve Posterior scrotal nerves, Anterior scrotal nerves, genital branch of genitofemoral nerve, perineal branches of posterior femoral cutaneous nerve
Lymph Superficial inguinal lymph nodes
Identifiers
Latin Scrotum
MeSH A05.360.444.661
Dorlands
/Elsevier
12726162
TA A09.4.03.001
FMA 18252
Anatomical terminology

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, which functions 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, as well as in some lineages of land mammals, such as the afrotherians, xenarthrans, and numerous families of bats, rodents, and insectivores.[2][3]

Contents

StructureEdit

InnervationEdit

Nerve Surface[4]
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 supplyEdit

Blood vessels[5]
Anterior scrotal artery
Posterior scrotal artery
Testicular artery

IntegumentEdit

Skin associated tissues [5]
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. [6]

Lymphatic systemEdit

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[7]
Superficial inguinal lymph nodes
Popliteal lymph nodes
Popliteal lymph nodes

DevelopmentEdit

Genital homology between sexesEdit

Main article: Sexual homology

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.[8]

AsymmetryEdit

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.[9]

Scrotal growth and pubertyEdit

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.[10]

Internal structureEdit

FunctionEdit

 
Image showing musculature and inner workings of the scrotum.

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[11] 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).[10]

 
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.

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.[11] Another advantage is it protects the testes from jolts and compressions associated with an active lifestyle. Animals that have stately movements – such as elephants, whales, and marsupial moles – have internal testes and no scrotum.[12] Unlike placental mammals, male marsupials have a scrotum that is anterior to the penis.[13][14][15] In some sex positions, such as doggystyle the scrotum may provide friction for the clitoris, and may subsequently serve as an impetus for sexual pleasure or orgasm in the woman.[16]

Clinical significanceEdit

A study has indicated that use of a laptop computer positioned on the lap can negatively affect sperm production.[17][18]

Diseases and conditionsEdit

See alsoEdit

This article uses anatomical terminology; for an overview, see Anatomical terminology.

BibliographyEdit

Books
  • This article incorporates text in the public domain from 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 0697056759. 
  • Elson, Lawrence; Kapit, Wynn (1977). The Anatomy Coloring. New York, New York: Harper & Row. ISBN 0064539148. 
  • "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 0911910875. 

ReferencesEdit

  1. ^ a b Anthony F.Bogaert, "Genital asymmetry in men", Human Reproduction vol.12 no.1 pp.68–72, 1997. PMID 9043905.
  2. ^ "Scrotum". National Institutes of Health. Retrieved 6 January 2011. 
  3. ^ Lovegrove, B.G. 2015. "Cool sperm: why some placental mammals have a scrotum." Journal of Evolutionary Biology. 27(5):801-814. doi: 10.1111/jeb.12373
  4. ^ Moore, Keith; Anne Agur (2007). Essential Clinical Anatomy, Third Edition. Lippincott Williams & Wilkins. p. 132. ISBN 0-7817-6274-X. 
  5. ^ a b Elson 1977.
  6. ^ "Scrotum". Encyclopædia Britannica. Retrieved 2015-02-24. 
  7. ^ "VIII. The Lymphatic System. 5. The Lymphatics of the Lower Extremity. Gray, Henry. 1918. Anatomy of the Human Body.". Retrieved 2015-02-24. 
  8. ^ Van de Graaff 1989, p. 927-931.
  9. ^ Gallup, G. G., Jr., Finn, M. M., & Sammis, B. "On the origin of descended scrotal testicles: The activation hypothesis., Evolutionary Psychology, 7, 2009, p. 517-524.
  10. ^ a b Van de Graaff 1989, p. 935.
  11. ^ a b Van de Graaff 1989, p. 936.
  12. ^ "Science : Bumpy lifestyle led to external testes - 17 August 1996 - New Scientist". New Scientist. Retrieved 2007-11-06. 
  13. ^ Hugh Tyndale-Biscoe; Marilyn Renfree (30 January 1987). Reproductive Physiology of Marsupials. Cambridge University Press. ISBN 978-0-521-33792-2. 
  14. ^ Libbie Henrietta Hyman (15 September 1992). Hyman's Comparative Vertebrate Anatomy. University of Chicago Press. pp. 583–. ISBN 978-0-226-87013-7. 
  15. ^ Menna Jones; Chris R. Dickman; Michael Archer (2003). Predators with Pouches: The Biology of Carnivorous Marsupials. Csiro Publishing. ISBN 978-0-643-06634-2. 
  16. ^ Jones, Richard (2013). Human Reproductive Biology. Academic Press. p. 74. The rear-entry position of mating may allow the scrotum to stimulate the clitoris and, in this way, may produce an orgasm ... 
  17. ^ "Laptops may damage male fertility". BBC News. 2004-12-09. Retrieved 2012-01-30. 
  18. ^ 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. 
  19. ^ "Paget's disease of the scrotum Symptoms, Diagnosis, Treatments and Causes". RightDiagnosis.com. Retrieved 2015-02-24. 
  20. ^ "Common scrotal skin diseases". TCMWell. Retrieved 2015-02-24. 
  21. ^ a b TCMwell.