Sexual differentiation and disorders Flashcards
what is sexual determination?
whether you are female (xx) or male (xy)
what is sexual differentiation?
process by which internal and external genitalia develop as male or female
what are the 5 stages of sexual differentiation of the embryo?
1)Genotypic sex= either xx or xy
2)Gonadal sex=Formation of either ovaries or testes
3)Phenotypic sex=the shape and outward appearance of the genital region
4)Legal sex= what’s on your birth certificate
5)Gender identity= how you feel and what you identify as
what gene is found on the Y chromosome? and what is it’s function?
The SRY gene, which is a transcription factor. Once transcribed it will form the SRY protein, transcription of itself in a positive feedback mechanism it then causes a cascade of transcription events (transcription of other genes), which results in forming the testes
Testes develop and contain 2 cells that make 2 important hormones. what are they?
1)Sertoli cells= AMH
2)Leydig cells= testosterone
If you have no SRY gene what happens?
Ovaries develop. Even if the Y chromosome has no SRY gene the ovaries develop so SRY is the trigger for sexual differentiation
what is the precursor for gonadal development?
Genital ridge primordia ( a common somatic mesenchymal tissue precursor)
so what can the genital ridge become when SRY is expressed/not expressed?
ovaries (SRY not expressed) or testes (SRY expressed)
what are the 2 ducts found behind the genital ridge?
1) Mullein ducts= develop into uterus, uterine tubes and upper 1/3rd of the vagina
2)Wolffian ducts=develop into the vas deferens, epididymis and part of the prostate
what are the 3 types of cells that invade the genital ridge?
1) Primordial Germ cell
2) Primitive Sex cords
3) Mesonephric Cells
what do the Primordial Germ cells become?
Become Sperm (male) or Oocytes/immature egg (females)
what do the Primitive sex cords become?
Steroli cells (male) or Granulosa cells (female)
Explain Primordial Germ cell migration
Small cluster of cells in the epithelium of the yolk sac expands by mitosis at around 3 weeks, migrating to the connective tissue of the hind gut, to the region of the developing kidney and on to the genital ridge. These cells can become sperm or egg. Will develop into sperm or eggs after 6 weeks?
Explain Primitive sex cords (Sertoli/ Granulosa) in developing into Sertoli or Granulosa
cells from the epithelium that overline the genital ridge move inwards as columns, these are known as primitive sex cords. In males due to the expression of the SRY gene these primitive sex cords develop into Sertoli cells whilst in women no expression so they develop into Granulosa.
Describe What happens in males at the primitive sex cords
1) sry expression occurs in males
2) Penetrate the medullary mesenchyme and surround the primordial germ cells to form the testes
3) Eventually become Sertoli cells which express Anti-mullerian hormone (AMH)
4)They form the long tubular structures with the germ cells (become the precursor of seminiferous tubules)
Describe what happens in females at the primitive sex cords
1)There is no SRY expression
2)Sex cords are ill defined and do not penetrate deeply but instead condense in the cortex as small clusters around the Primordial germ cells
3)Eventually become the granulosa cells
They surround the germ cells in clumps and this is like the follicle when th eggs are surrounded by clumps in the ovary= characteristic shape forming
what is the 3rd type of cells that migrates and invades the genital ridges in the embryo?
The Mesonephric cells
Where do the mesonephric cells originate from?
The mesonephric ridge/ mesonephric primordium, which is found beside the genital ridges
what do the mesonephric cells develop into?
males=Leydig cells (primary source of testosterone)
Females= Theca cells
what influences the mesonephric cells and what affect does this have/ what forms?
They are influenced by pre-sertoli cells (which themselves express SRY) to form:
1) Vascular tissue
2) Leydig cells (synthesise testosterone, do not express SRY)
3)Basement membrane- contributing to formation of seminiferous tubules and retests
Describe how the mesonephric cells become Leydig cells
The AMH and Sertoli cells make testosterone together and the Sertoli cells secrete AMH and the GF’s stimulate the mesonephric cells to become the Leydig cells
In the absence of SRY expression what happens to the mesonephric cells?
1) Form Vascular tissue
2) Form Theca cells
Describe the hormonal changes in the early stage of the embryo development in males and females.
in males there is AMH produced (via Sertoli cells) and testosterone (via Leydig cells) whilst in the female you have nothing produced as of yet. In the absence of these male hormones the female system develops.
what are the the 3 invading cells and what do they go on to form in males?
1)Primordial germ cells= sperm
2) Primitive sex cords= Sertoli cells (SRY and AMH)
3) Mesonephric cells= Leydig cells (androgens/testosterone)
