Sexual differentiation and disorders

Question 1

what is sexual determination?

Answer 1

whether you are female (xx) or male (xy)

Question 2

what is sexual differentiation?

Answer 2

process by which internal and external genitalia develop as male or female

Question 3

what are the 5 stages of sexual differentiation of the embryo?

Answer 3

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

Question 4

what gene is found on the Y chromosome? and what is it’s function?

Answer 4

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

Question 5

Testes develop and contain 2 cells that make 2 important hormones. what are they?

Answer 5

1)Sertoli cells= AMH
2)Leydig cells= testosterone

Question 6

If you have no SRY gene what happens?

Answer 6

Ovaries develop. Even if the Y chromosome has no SRY gene the ovaries develop so SRY is the trigger for sexual differentiation

Question 7

what is the precursor for gonadal development?

Answer 7

Genital ridge primordia ( a common somatic mesenchymal tissue precursor)

Question 8

so what can the genital ridge become when SRY is expressed/not expressed?

Answer 8

ovaries (SRY not expressed) or testes (SRY expressed)

Question 9

what are the 2 ducts found behind the genital ridge?

Answer 9

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

Question 10

what are the 3 types of cells that invade the genital ridge?

Answer 10

1) Primordial Germ cell
2) Primitive Sex cords
3) Mesonephric Cells

Question 11

what do the Primordial Germ cells become?

Answer 11

Become Sperm (male) or Oocytes/immature egg (females)

Question 12

what do the Primitive sex cords become?

Answer 12

Steroli cells (male) or Granulosa cells (female)

Question 13

Explain Primordial Germ cell migration

Answer 13

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?

Question 14

Explain Primitive sex cords (Sertoli/ Granulosa) in developing into Sertoli or Granulosa

Answer 14

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.

Question 15

Describe What happens in males at the primitive sex cords

Answer 15

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)

Question 16

Describe what happens in females at the primitive sex cords

Answer 16

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

Question 17

what is the 3rd type of cells that migrates and invades the genital ridges in the embryo?

Answer 17

The Mesonephric cells

Question 18

Where do the mesonephric cells originate from?

Answer 18

The mesonephric ridge/ mesonephric primordium, which is found beside the genital ridges

Question 19

what do the mesonephric cells develop into?

Answer 19

males=Leydig cells (primary source of testosterone)
Females= Theca cells

Question 20

what influences the mesonephric cells and what affect does this have/ what forms?

Answer 20

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

Question 21

Describe how the mesonephric cells become Leydig cells

Answer 21

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

Question 22

In the absence of SRY expression what happens to the mesonephric cells?

Answer 22

1) Form Vascular tissue
2) Form Theca cells

Question 23

Describe the hormonal changes in the early stage of the embryo development in males and females.

Answer 23

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.

Question 24

what are the the 3 invading cells and what do they go on to form in males?

Answer 24

1)Primordial germ cells= sperm
2) Primitive sex cords= Sertoli cells (SRY and AMH)
3) Mesonephric cells= Leydig cells (androgens/testosterone)

Question 25

what are the the 3 invading cells and what do they go on to form in females?

Answer 25

1) Primordial germ cells= oocytes
2) Primitive sex cords= Granulosa cells (FSH and oestrogen)
3)Mesonephric cells= Theca cells

Question 26

What are the 2 ducts?

Answer 26

1) Mullerian duct (females)
2)Wolffian duct (males)

Question 27

what does the Müllerian duct develop into?

Answer 27

The uterus, uterine tube and the upper 1/3rd of the vagina.

Question 28

what does the Wolffian duct develop into?

Answer 28

The Vas deferens, epididymis and part of the prostate.

Question 29

what hormone causes the Müllerian duct to be inhibited in both males and females?

Answer 29

AMH/ Anti mullerian hormone
If there is no AMH in females they grow

Question 30

what hormone causes the regression of the Müllerian ducts in females?

Answer 30

Testosterone

Question 31

since there is no release of hormones in the female embryo at the early stage of development what does the mean in terms of the Müllerian duct and the Wolffian duct?

Answer 31

they can grow since they won’t be affected by AMH or testosterone. Since there is no testosterone the Wolffian duct can not grow.

Question 32

what hormone causes the growth of the Wolffian duct in males?

Answer 32

Testosterone

Question 33

What is the name of the enzyme on the external genitalia skin? and what is its function?

Answer 33

5-alpha-reductase. This converts testosterone to dihydrotestosterone (DHT) by adding an extra hydrogen on.

Question 34

why does testosterone get converted to DHT?

Answer 34

since it is a more powerful steroid compared to testosterone and it binds to the same receptors, causing a greater reaction.

Question 35

DHT causes differentiation of the male external genitalia. Describe the changes (3)

Answer 35

1) Clitoral area enlarges into the penis
2)Labia fuse and become ruggated to form Scrotum
3) Prostate forms

Question 36

do females have 5-AR? what does this mean?

Answer 36

no. this means you get no testosterone produced so you have the female system produced.

Question 37

Describe the process of sex differentiation in males

Question 38

Describe the process of sex differentiation in females