Sex Determination and Differentiation Flashcards
What are the aims of the male reproductive system?
- to produce, maintain, transport and nourish sperm an semen
- to discharge sperm within the female reproductive tract
- to produce and secrete male sex hormones
What are the male external genitalia?
penis and scrotum
What is the male gonad?
testis
What are the male internal genitalia?
- seminal vesicle
- ejaculatory duct
- vas deferens
- epididymis
What are the aims of the female reproductive system?
- to release eggs, which can potentially be fertilised by sperm
- to produce and secrete female sex hormones
- to provide an environment for a fertilised egg to develop during pregnancy
- to facilitate labour and childbirth
What are the female external genitalia?
- clitoris
- labia
- vagina
What is the female gonad?
ovary
What are the female internal genitalia?
- uterine duct
- uterus
- vagina (upper 1/3)
What are the 3 levels that determine the sex of a person?
- genetic sex
- gonadal sex
- phenotype sex
When is genetic sex determined?
at the time of fertilisation
How many chromosomes do somatic and gamete cells have respectively?
- somatic = 46 (23 pairs)
- gamete = 23
What are the sex chromosomes in males and females respectively?
- male = XY
- female = XX
What does genetic sex determine?
gonadal sex
What determines gonadal differentiation?
presence or absence of a Y chromosome
What can the gonadal ridge form?
either ovary or testis
What happens at 1.5 months of gestation?
- all embryos have a potential to differentiate along either male or female lines
- the developing reproductive tissues of both sexes are identical and undifferentiated
When is gonadal sex determined in males and females respectively?
- males = week 7
- females = week 9
What is the SRY gene?
the sex determining region of the short arm of the Y chromosome that encodes the protein TDF (testis-determining factor)
What does TDF do?
act as a TF for the genes necessary for testicular differentiation, including MIF and androgen receptors
What does MIF do?
initiate the development of male glands
Why do females not produce TDF?
they lack the SRY gene
What does the cloaca form?
the male and female external genitalia
Which ducts form the male and female internal genitalia?
- male = Wolffian
- female = Müllerian
What happens if the undifferentiated glands are removed before testes have developed at 7 weeks?
the Wolffian gland development is inhibited and so no MIF is produced and ovaries form
What is required for male differentiation?
- Y chromosome must be present
- SRY gene must work to produce MIF
- hormones must be present
What does testosterone do?
convert to DHT which allows the Cloaca to form the external male genitalia
What enzyme converts testosterone to DHT?
5α reductase
What is aneuploidy?
abnormal number of chromosomes
What causes Turner’s syndrome?
having a single X chromosome
What are the symptoms of Turner’s syndrome?
webbed feet, short stature, failure of ovaries to develop, absence of menstrual cycle
Give an example of a gonadal sex disorder
abnormal development of gonads (incomplete differentiation) and so not functional to induce puberty
Give an example of a phenotypic sex disorder
male/female pseudo hermaphroditism
What is pseudo hermaphroditism?
a condition in which an organism is born with secondary sex characteristics or a phenotype that is different from what would be expected on the basis of the gonadal tissue (ovary or testis)
What is an hermaphrodite?
one bearing characteristics of both sexes
What is lacking in male pseudo hermaphroditism?
- hormones (testosterone, MIF)
- enzymes (5α-reductase, enzymes involved in steroid synthesis)
- receptors (androgen receptors, LH receptor)
What does female pseudo hermaphroditism arise from?
exposure to androgens (male sex hormone) by maternal exposure or androgen excess in foetus
What are the symptoms of 21-hydroxylase deficiency in females?
- abnormal menstrual periods
- deep voice
- early appearance of pubic and armpit hair
- excessive hair growth and facial hair
- failure to menstruate
- genitals that look both male and female (ambiguous genitalia), often appearing more male than female
What is a significant stage in sexual development of males?
descent of the testes in the 7th month of gestation
What is undescended testes into adulthood and what is its incidence?
cryptorchidism and its incidence is 3% of full-term babies and 30% of premature babies
What is spermatogenesis dependent on?
temperature (needs to occur 2ºC cooler than normal body temperature)
How long does spermatogenesis take?
64 days
What cell type produces testosterone?
Leydig cells
What provides nutrients and support for spermatogenesis?
Sertoli cells
What does the hypothalamus do at puberty?
secrete GnRH to stimulate the anterior pituitary to make and release LH and FSH
How are LH and FSH secreted?
in a pulsatile manner ~every 1-3 hours
What happens if there is continuous exposure of gonadotrophs to GnRH?
desensitisation of GnRH receptors, leading to a decrease in LH and FSH release
How is GnRH a tropic hormone?
it stimulates the testes to make testosterone
What does the negative feedback loop of testosterone levels do?
decrease GnRH release by acting on the hypothalamus to indirectly decrease both LH and FSH release
How does testosterone work?
by binding to plasma proteins in circulation (can also bind to albumin but not with the same affinity)
What are the effects of testosterone?
- internal male genitalia (differentiation)
- pubertal growth spurt
- penis (growth)
- deepening of voice
- spermatogenesis
- libido
- muscle mass and recovery
What are the effects of taking exogenous hormone (anabolic steroid)?
the testes would not achieve normal testosterone levels since they are not receiving normal stimulatory input causing testosterone secretion and sperm production to decrease and the testes to shrink
How much more active is DHT than testosterone?
more than 2x
Where is 5α-reductase high?
skin, prostate gland, seminal vesicle, epididymis, testes and liver
What are the effects of DHT?
- external male genitalia (differentiation)
- sebaceous glands
- prostate (growth)
- male hair pattern baldness
What does DHT do to hair?
cause shrinkage in the overly sensitive hair follicles which causes them to fall out
What is spermatogenesis?
production of sperm
Give an example of a post testicular abnormality
failure in sperm storage, transport, nourishment, and release
Give an example of a pretesticular abnormality
- failure in the entire male repo functions
- GnRH deficiency
