Normal sexual differentiation

Question 1

sexual determination

Answer 1

genetically controlled process dependent on the switch on the Y chromosome, determination of male or female.

Question 2

sexual differentiation

Answer 2

process by which internal and external genitalia develop as males or females.

Question 3

SRYgene

Answer 3

• on the y chromosome
• when this gene is switched on testis develop at week 7
  -in the absence of Y chromosome = no SRY gene so ovaries develop.

Question 4

What are the cells of testis and what 2 hormones do they make?

Answer 4

1. Leydig - makes testosterone
2. Sertoli - produce AMH
   => production of these two hormones influences further development of gonodal phenotypic features.

Question 5

What is SOX9?

Answer 5

• SRY is a DNA binding protein that acts as a transcription factor and bind to SOX9 to turn it on.
  -SOX9 is also a transcription factor
  -Binding of SRY to SOX9 stimulates the turning on of testicular genes and turning off ovarian genes to develop a foetus into a male.

Question 6

Why can SOX9 work even in the absence of SRY?

Answer 6

SOX9 is independent of SRY bc it can produces fibroblast growth factors which enhances sox9 production , it is autocrine and bind to its own upstream activation site so its levels remain high (positive mechanism).

Question 7

How does SOX9 achieve its effects?

Answer 7

1. stimulates production of prostaglandin D2 (PGD2) by the pre-sertoli cells.
2. PGD2 acts as a paracrine hormone to stimulate further production pof SOX9 in these pre-sertoli cells (second positive feedback).
3. SOx9 stimulates the production of anti- Mullerian (AMH). AMH causes the regression of the mullerian ducts which develop into the uterus and fallopian tubes in the female developing into male testis
4. Inhibition of female transcription factors WNT4 and FOXL2 thus developing into male testis

Question 8

Transcriptional pathway in serotoli cell

Answer 8

Question 9

mechanism pathway in the granulosa cell

Answer 9

Question 10

When do gonads develop?

Answer 10

-after fertilisation a pair of gonads develop which are bipotential

Question 11

what tissue is the precursor of gonads derived from and where?

Answer 11

-common somatic mesenchymal tissue precursors called genitial ridge primordial (3 to 4 weeks)
-in the posterior wall of lower thoracic lumbar region.

Question 12

what 3 waves of cells invade the genital ridge?

Answer 12

1.primordial germ cells
2. primitive sex cords
3. mesenpheric cells

Question 13

primordial germ cells

Answer 13

-initially small cluster of cells in the epithelium of yolk sac expands by mitosis aroun 3 weeks

Question 14

primitive cord

Answer 14

-cells from germinal epithelium that overlies the genital ridge mesenchyme migrate inwards as columns called primitive sex cords
- females = no SRY expressed, no deep penetration of sex cords, follicle formed and granulosa cells
-males = SRY expressed, develop testis cords and seminiferous vesicles and Sertoli cells

Question 15

mesenpheric cells

Answer 15

• occur in mesenephric primordium which are lateral to the genital ridges
  -males : act under influence pf pre-sertoli (which express SRY) cells to form leydig cells, basement membrane, vascular tissue
  -females: without influence of SRY they form vascular tissue, and theca cells.

Question 16

What do primordial germ cells become?

Answer 16

males: sperms
females: oocytes

Question 17

What do primitive sex cords become?

Answer 17

boy: sertoli
girl: granulosa

Question 18

What do mesenpheric cells become?

Answer 18

males: leydig cells
females: theca cells
+blood vessels

Question 19

What are female internal reproductive ducts?

Answer 19

Mullerian ducts:
- most important in females
-inhibited in males by AMH

Question 20

What are male internal reproductive ducts?

Answer 20

wolfian ducts
- stimulated by testosterone
-lack of stimulation by testosterone in female leads to regresssion of the duct.

Question 21

What hormone is involved in the external genital differentiation?

Answer 21

-5 alpha-reductase
-testosterone => dihydrotestosterone (DHT) by this enzyme
-dihydrotestosterone is what causes the differntiation of external male genitalia

Question 22

How does DHT lead to differentiation of male genitalia

Answer 22

-DHT is more potent than testosterone and binds to testosterone receptors with higher affinity, causing differentiation of male genitalia:
1. clitoris area enlarges to penis
2. labia fuse and become ruggated from scrotum
3. prostate forms.

Question 23

Sex differentiation summary

Answer 23

Question 24

define sex

Answer 24

biological aspect of an individual as determined by their anatomy , which is produced by their chromosomes and hormones

Question 25

define gender

Answer 25

defined as a social construction relating to behaviours and attributes based on labels oof masculinity and femininity Historically there has been a general assumption that a single feature such as the presence/absence of a penis would predict that all the other gender features to be concordantly male or female. Gender attributes are based on attitudes, expectations, behaviours or roles which may be highly complex

Question 26

gender identity

Answer 26

personal, internal perception of onself. An individual may see themselves as a man, woman or having no gender, where people identify as somehwere on a spectrum.

Question 27

gender role

Answer 27

expression or portrayal of psychological characteristics that are considered sexually dimorphic within general population

Question 28

sexual orientation

Answer 28

preference of sexual partner and erotic interest (includes heterosexual, bisexual, homosexual)

Question 29

psychosexual neutrality

Answer 29

The view that gender assignment of a newborn with ambigious genitalia can be made regardless of endocrine history

Question 30

neural bias

Answer 30

the idea that a tendency for male or female is already present in neonates as a result of prenatal factors such as hormonal milieu in utero

Question 31

how is hormones and behaviour linked?

Answer 31

exposing animals to sex hormones during critical period before or just after birth is associated with sexual divergent (different sexes)

Question 32

Examples of animal studies to show the hormonal and sexual link

Answer 32

1. dog breeders wait until dog has learned to cock its leg before neutering (if they are neutered early this behaviour never occurs, so cant be learned behaviour) 2. treatment of female mice with testosterone in first 5 days of life increases their display of masculine sexual behaviour in adulthood and decreases female patterns => castration of male rats during this period removes the influence of androgens and has reverse effects =>androgens may influence the development of these behavioural differences by acting on structure of developing brain.

Question 33

Nature: gender differences in the brain

Answer 33

-numerous genes are differentially expressed in males and female embryonic brains -both morphological and functional differences in human brain structure according to sex have been found : 1. amygdala larger in males - which correlates with increased aggressive behaviour in males. 2. left amygdala larger in females - region associated with emotions 3. hippocampus contains more grey matter in females : involved in memory and social cognition 4. third intersitial nucleus of the anterior hypothalamus (INAH-3) has been suggested to be a major determinant of sexual identity. may be larger in heterosexual males than homosexual males and heterosexual females.

Question 34

How can you interpret a functional MRI (fMRI)

Answer 34

-increased activity in certain regions of brain , more oxygen used so more blood flow appears red. -neuroimaging has shown functional sex differences in a variety of brain regions when subjects undergone activities related to emotion, memory , language etc. - evidence of certain bilateral differences between two genders

Question 35

Nurture : social learning

Answer 35

when adults are handed a baby and they are told the baby is a boy or a girl the way they play with it is different. study : adults were asked to watch a film of a child at play, half were told it was a girl and other half told it was a boy. findings: those who were told it was a boy thought the baby was angry when it was startled whereas those who though it was a girl thought the baby showed signs of distress.

Question 36

timeline of social learning

Answer 36

by the age of 2 children consistently label themselves as male or female by the age if 5 they appear to have sense of gender constancy (believe their gender cant be changed) 3-6 yo develop gender stereotypes more rigid than adults. => evidence supports the view that gender stereotypes are applied to babies and children themselves apply them from an early age

Question 37

summary

Answer 37

- some gender patterns of behaviour may be induced by the way boy and girls are treated or as a result of the exceptions of others. -differentiation of the human brain is partly due the hormonal environment in utero and/or neonatally - even before foetal hormone levels rise there are numerous genes expressed differently in male and female brains -psychosexual development is not fully understood and remains the focus active research and investigation.