Scrotum

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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
Latin Scrotum
Precursor labioscrotal folds
Anterior scrotal artery & Posterior scrotal artery
Testicular vein
Posterior scrotal nerves, Anterior scrotal nerves, genital branch of genitofemoral nerve, perineal branches of posterior femoral cutaneous nerve
Superficial inguinal lymph nodes
Identifiers
Gray's p.1237
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 sack of skin and smooth muscle that is dual-chambered, present in most terrestrial male mammals and is located under the penis. The left testis is lower than the right to avoid compression in the event of impact. The perineal raph is a small, vertical, slightly raised ridge of scrotal skin under which scrotal septum exists. 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, ductus deferens. Stream-lined, aquatic mammals such as whales and seals typically lack an external scrotum.[1] It is an distention of the perineum and carries abdominal tissues some into its cavity including the testicular artery, testicular vein and pampinform plexus. In humans and some other mammals, the scrotum becomes covered with pubic hair at puberty.

The scrotum is biologically homologous to the labia majora in females.

Structure[edit]

Innervation[edit]

Nerve Surface[2]
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[edit]

Blood vessels[3]
Anterior scrotal artery
Posterior scrotal artery
Testicular vein

Integument[edit]

Skin associated tissues [3]
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. [4]

Lymphatic system[edit]

Lymphatic vessels[5]
Superficial inguinal lymph nodes
The Superficial Subinguinal Glands (lymphoglandulæ subinguinales superficiales)
The Deep Subinguinal Glands (lymphoglandulæ subinguinales profundæ)

Development[edit]

Genital homology between sexes[edit]

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 ogans 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.[6]

Scrotal growth and puberty[edit]

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.[7]

Internal structure[edit]

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

Function[edit]

Image showing musculature and inner workings of the scrotum.

The function of the scrotum is to keep the temperature of the testes at about 35-36 degrees Celsius (95-96.8 degrees Fahrenheit), i.e. one to two degrees below the body temperature of 37 degrees Celsius (98.6 degrees Fahrenheit).[8] High scrotum temperature is damaging to sperm production.[citation needed] 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).[citation needed]

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.[9] Some mammals — elephants and marine mammals, for example – do keep their testes within the abdomen and there may be mechanisms to prevent this inadvertent emptying.

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.

Abdominal muscles, and changes in intra-abdominal pressure, can often lift and lower the testicles within the scrotum. Contraction of the muscle fibers of the dartos tunic (or fascia) is completely involuntary and results in the appearance of increased wrinkling and thickening of the scrotal skin. The testicles are not directly attached to the skin of the scrotum, so this dartos contraction results in their sliding toward the abdomen. They also, in some men, can be lifted the same way by tightening the anus and pelvic muscles, doing Kegel exercises.

Although the ideal temperature for sperm growth varies between species, it usually appears, in warm-blooded species, to be a bit cooler than internal body temperature, making the scrotum necessary. Since this leaves the testicles vulnerable in many species, there is some debate on the evolutionary advantage of such a system. One theory is that the impregnation of females who are ill is less likely when sperm is highly sensitive to elevated body temperatures. An alternative explanation is to protect 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.[10]

Clinical significance[edit]

A study has indicated that use of a laptop computer positioned on the lap can negatively affect sperm production.[11][12]

Diseases and conditions[edit]

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

See also[edit]

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

Bibliography[edit]

Books
  • This article incorporates text from a public domain edition of Gray's Anatomy.
  • 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. 

References[edit]

  1. ^ "Scrotum". National Institutes of Health. Retrieved 6 January 2011. 
  2. ^ Moore, Keith; Anne Agur (2007). Essential Clinical Anatomy, Third Edition. Lippincott Williams & Wilkins. p. 132. ISBN 0-7817-6274-X. 
  3. ^ a b Elson 1977.
  4. ^ "Scrotum". Encyclopedia Britannica. Retrieved 2015-02-24. 
  5. ^ "VIII. The Lymphatic System. 5. The Lymphatics of the Lower Extremity. Gray, Henry. 1918. Anatomy of the Human Body.". Retrieved 2015-02-24. 
  6. ^ vandegraaff 1989, p. 927-931.
  7. ^ vandegraaff 1989, p. 935.
  8. ^ "About the Male Reproductive System". KidsHealth. Retrieved 6 January 2011. 
  9. ^ "Science : Bumpy lifestyle led to external testes - 17 August 1996 - New Scientist". Retrieved 2007-11-06. 
  10. ^ "Science : Bumpy lifestyle led to external testes - 17 August 1996 - New Scientist". Retrieved 2007-11-06. 
  11. ^ "Laptops may damage male fertility". BBC News. 2004-12-09. Retrieved 2012-01-30. 
  12. ^ 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. 
  13. ^ "Paget's disease of the scrotum Symptoms, Diagnosis, Treatments and Causes". RightDiagnosis.com. Retrieved 2015-02-24. 
  14. ^ "Common scrotal skin diseases". TCMWell. Retrieved 2015-02-24. 
  15. ^ a b TCMwell.
  16. ^ Uwe, Wollina (Sep 21, 2011). "Red scrotum syndrome". J Dermatol Case Rep 5 (3): 38–41. doi:10.3315/jdcr.2011.1072.