sex differences

Question 1

what are organisational effects of sex hormones produced by fetal gonads

Answer 1

permanent alterations in body or CNS induced by a hormone at a critical period in development

Question 2

what is the activational effect of sex hormones produced by gonads

Answer 2

hormone effects that occur in the fully developed organism; depend on the previous organisational effects

Question 3

what are internal sex organs

Answer 3

• precursor for female internal sex organs
• precursor for male internal sex organs

Question 4

what factors determine the development of male sex organs

Answer 4

• starts with XY chromosome
• enter process of male differentiation
• primordial gonads develop into testes
• tested produce hormones that lead to defeminisation and masculinisation

Question 5

what is the region on the Y chromosome in male differentiation

Answer 5

SRY region on Y chromosome codes for testsis-determining factor that binds to DNA in cells of undifferentiated gonads and causes them to become testes

Question 6

what does the anti-mullerian hormone (defeminisation) lead to

Answer 6

mullerian system withers away

Question 7

what do androgens lead to (masculinisation)

Answer 7

• wolffian system develops into vas deferens, seminal vesicles, prostate
• primordial external genitalia develop into penis and scrotum

Question 8

what is the testis-determining factor

Answer 8

• 230 amino-acid long protein coded for by SRY region of Y chromosome
• transcription factor binding DNA, thereby, inducing confromational changes that enable transcription
• point mutations can prevent development of testes (and hence of internal and external male sex organs) in XY individuals

Question 9

what is the anti-mullerian hormone

Answer 9

a peptide secreted by the fetal testes that has defeminising effects i.e. inhibits the development of the mullerian system by acting on anti-mullerian hormone receptors in cells of that system

Question 10

what are the two types of androgens

Answer 10

• testosterone
• dihydrotestosterone

Question 11

what is testosterone

Answer 11

• primary cause of masculisation during early development
• acts on androgen receptors in cells of the wolffian system and stimulates it’s development into male internal sex hormones

Question 12

what is dihydrotestosterone

Answer 12

• produced from testosterone by 5alpha reductase, acts on androgen receptors in the primordial external genitals (with higher affinity than testosterone) and is critical to stimulate their development into male genitals

Question 13

factors determining the development of female sex organs

Answer 13

• XX chromosome
• primordal gonad develops into ovaries
• no hormones needed
• mullerian system develops into fimbriae fallopian tubes, uterus, inner vagina
• wolffian systems, without androgens, withers away
• primordial externa genitalia develop into clitoris, labia, outer vagina

Question 14

what is XY sex reversal

Answer 14

point mutations in the SRY region of the Y chromosome result in female sex organs in XY individuals

Question 15

what is androgen insensitivity syndrome

Answer 15

• a condition caused by congenital lack of functioning androgen receptors, in person with XY sex chromosomes, causes development of a female with testes but no internal sex organs

Question 16

what is turner’s syndrome

Answer 16

the presence of only one sex chromsome results in the lack of ovaries but otherwise normal female sex organs and genitalia

Question 17

what is persistent mullerian duct syndrome

Answer 17

• in an XY individual, congenital lack of anti-mullerian hormone causes the development of both male and female external sex organs

Question 18

what is puberty triggered by

Answer 18

hypothalamic secretion of gonadotropin-releasing hormone

Question 19

what is the hormonal process of puberty

Answer 19

• hypothalamus releases GnRH which acts on the pituitary gland which releases gonadotropic hormones which stimulate male or female components and releases testosterone or estradiol which leads to secondary sex characteristics

Question 20

what are steroid hormones

Answer 20

androgens, estrogens

Question 21

what are peptide hormones

Answer 21

gestagens, hypothalamic hormones, gonadotropins

Question 22

what is sexual/copulatory behaviour

Answer 22

sexual behaviour is stereotypical in rodents and non-humans - lordosis response

Question 23

what is the organisational hypothesis

Answer 23

• based on findings that exposing female rats and guinea pigs to androgen in utero during critical periods altered their adult sex behaviour, william young and colleagues proposed that early androgens, similar to their effects on sex organs, organise the developing CNS in a masculine way, so as to make female behaviours less likely and male behaviours more likely - Young et al 1964

Question 24

what evidence supports the organisational hypothesis

Answer 24

• since publication of the organisational hypothesis, many sex differences in the CNs have been reported in many vertebrates, including humans
• many neural sex differences in rodents have been demonstrated to depend on organisational effects of androgens during the critical development periods
• other neural sex differences have been demonstrated to depen on organising and activating effects of androgens and yet others only involve activating effects during adulthood
• there is evidence that neural sex differences contribute substantially to sex differences in behaviour, often in conjunction with activating effects of sex hormones on sexually dimorphic neural systems

Question 25

what is the aromatisation hypothesis

Answer 25

in some CNS cells testosterone is converted to estrogen by an enzyme called aromatase before it acts on estrogen receptors to exert masculinising effects

Question 26

what is the protection hypothesis

Answer 26

the brains of developing rodents are protected from the indiscriminate masculinising action of estrogen by an estrogen binding protein, alpha fetoprotein, in the blood. testosterone is not bound by the protein, so can enter CNS cells where it can be converted to estrogen and then exert its masculinising effects. hypothesis is strongly supported by finding that alpha-fetoprotein mutant mice show masculinised brains and behaviour

Question 27

what 3 factors are critical for mating to start in humans

Answer 27

- attractivity - proceptivity - receptivity

Question 28

what are the stages of mating behaviour

Answer 28

- appetitive - consummatory - post consummatory

Question 29

what is the spinal nucleus of the bulbocavernosus

Answer 29

- collection of motor neurons in the lower lumbar spinal cord; controls the bulbocavernosus muscle at the base of the penis - these motorneurons and muscles are necessary to normal penile reflexes that are important for successful copulation - they are absent or substantially reduce in size/number in adult females compared to males

Question 30

what do sex circuits contain

Answer 30

- sex hormone receptors, and these are critical for sex differences in mating behaviour; testosterone for male behaviour, estradiol and progesterone for female behaviour - several components show sex differences

Question 31

what are 2 components that show sex differences in sex circuits

Answer 31

- sexually dimorphic nucleus of the preoptic area - posterodorsal medial amygdala

Question 32

what did fliers and swaab 1985 find about sex differences in the preoptic area

Answer 32

- one nucleus in the POA of the hypothalamus was larger in volume and cell number in males than in females - authors named the nucleus SDN

Question 33

what did allen et al find about the sex differences in the preoptic area

Answer 33

- studied four nuclei in the POA, which they named interstitial nuclei of the anterior hypothalamus. INAH1 corresponded to SDN of flier and swaab but did not differ INAH2 and 3 were larger in men than in females