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