Difference between revisions of "Sexual Differentiation - Anatomy & Physiology"

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* Sex cord cells proliferate to form the testes cord.  During this period '''SRY''' is expressed for the first time within '''Sertoli cells''' (SRY is NOT expressed in primordial germ cells).
 
* Sex cord cells proliferate to form the testes cord.  During this period '''SRY''' is expressed for the first time within '''Sertoli cells''' (SRY is NOT expressed in primordial germ cells).
 
* Sex cords with a basement membrane become '''Semniferous Cords''' which give rise to '''Semniferous Tubules'''.
 
* Sex cords with a basement membrane become '''Semniferous Cords''' which give rise to '''Semniferous Tubules'''.
* Within the semniferous cords are two cell populations:
+
* '''Within the semniferous cords''' are two cell populations:
 
** '''Primordial germ cells'''  - Prospermatogonia which give rise to '''Spermatozoa'''
 
** '''Primordial germ cells'''  - Prospermatogonia which give rise to '''Spermatozoa'''
 
** '''Mesodermal cord cells''' which give rise to '''Sertoli cells'''
 
** '''Mesodermal cord cells''' which give rise to '''Sertoli cells'''
 
+
* '''Between cords''', the loose mesenchyme undergoes '''vascularisation''' and develops as '''stromal tissue'''.
 +
* Within the stromal tissue, cells condense into clusters to form specialized endocrine units - the interstitial '''Leydig Cells'''
  
 
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Revision as of 10:02, 3 July 2008

Genetic Sex

  • Established at the time of fertilisation.
  • The foetus receives its genetic endowment in two equal portions from the male gamete (Spermatozoon) and female gamete (Oocyte).
  • The X sex chromosome is larger than the Y sex chromosome.
  • Females have XX chromosomes. All oocytes contain one X chromosome, they are the homogametic sex.
  • Males have XY chromosomes. Spermatozoa form two distinct populations, one containing X chromosomes and one containing Y chromosomes. They are the heterogametic sex.


  • The Y chromosome is required to initiate male development.
  • In absence of the Y chromosome, female gonads (Ovaries) will develop.
  • The prime male determining gene is SRY (sex determining region of the Y chromosome.
  • SRY is a very small piece of DNA that acts as a molecular switch to regulate structural genes and autosomal chromosomes, determining if and when they are to be activated.
  • The presence of SRY alone is sufficient to ensure development of male gonads (Testes).
  • Female is the default sex, in absence of SRY female gonads (Ovaries) will develop.


  • Subsequent gonadal development is dependent on a normal population of germ cells.
  • Normal Oocyte growth requires the activity of both X chromosomes.
  • Normal Spermatogenesis requires the activity of no more than one X chromosome.



Internal Genetalia

  • Early development of gonads proceeds similarly in both sexes. The gonads are derived from two distinct tissues:
    • Somatic mesenchymal tissue forms the matrix of the gonad
    • Primordial germ cells form the gametes


  • Genital ridge forms from somatic mesenchyme.
  • Primordial germ cells migrate to the genital ridge.
  • At this stage it is not possible to discriminate between male and female gonads.
  • Y chromosomal determination of gonadal sex is only visible when primordial germ cell colonisation is complete.


MALE

  • Sex cord cells proliferate to form the testes cord. During this period SRY is expressed for the first time within Sertoli cells (SRY is NOT expressed in primordial germ cells).
  • Sex cords with a basement membrane become Semniferous Cords which give rise to Semniferous Tubules.
  • Within the semniferous cords are two cell populations:
    • Primordial germ cells - Prospermatogonia which give rise to Spermatozoa
    • Mesodermal cord cells which give rise to Sertoli cells
  • Between cords, the loose mesenchyme undergoes vascularisation and develops as stromal tissue.
  • Within the stromal tissue, cells condense into clusters to form specialized endocrine units - the interstitial Leydig Cells

External Genetalia

Turner's Syndrome
Kleinfelter's Syndrome
Testicular Feminisation
Adrenogenital Syndrome
Hermaphroditism
Bovine Freemartinism