puberty and sex differentiation Flashcards
what are primordial germ cells?
- indifferent between male/female until week 7
- diploid cell precursors -> arise during gastrulation at week 3 and are epiblast derived
- precursors to sperm/egg
what happens during weeks 3-7 ?
- cells proliferate via mitosis and migrate by amoebid movement to region of dorsal wall that will form the gonadal ridges –> guided via chemotaxis
what is important about week 7?
determines male or female development
- differences are present now
female (XX) / male (XY)
what is the importance of SRY?
- sex determining region y gene (on Y c)
- this is a conserved region across as mammals that encodes a controller gene testis determining factor gene
- this codes for a transcription factor (controller gene)
at what week Does does development of the testes begin?
week 7
1) columns of cells from coelomic epithelium proliferate and penetrate deeply ->sex cords-> express of SRY –> Sertoli cells
2) sex cords surround the PGCs–> forming seminiferous tubules
3) migratory cells from mesenophric primordial form vasculature and leydig cells
what do the sex cords form?
- Sertoli cells
what is found within the seminiferous tubules?
- prospermatogonia (the PGCs)
when does SRY expression stop?
once the sertoli and leydig cells form
- testes produce hormones leading to development of male reproductive system
what differs with ovary development?
- same 3 cells arrive but in the absence of SRY expression (behave differently)–> default
what is the default pathway?
- occurs from week 7 onwards
- absence of the Y chromosome (SRY(
- female gonad develops
briefly outline the order of ovarian development
- sex cord cells do not penetrate deeply and cluster around PGCs (oogonia) forming primordial follicles
- mesospheric cells form vasculature and thecae cells
- no endocrine activity
where is the wolffian duct and mullerian duct found?
WD–> male
MD–> female
gonads are bipotent, both structures exist at the indifference stage
what occurs in the testis under the action of androgens and MIS?
androgens-> from leydig cells maintain wolffian ducts (epididymis) and the vas deferens
- MIS–> from immature Sertoli cells–> causes regression of the mullerian ducts
what occurs in females under the absence of hormones?
- default pathway
- absence of AMH ducts develop
what occurs during the development of the male external genitalia?
- androgen converted to DH
T promotes male testes development - catalysed by 5a-RD
- the genital tubercle develops into the penis
- uro-genital fold develops into spongy urethra
- labio-scrotal swelling develops into scrotal sac
the female genitalia?
default pathway and no androgen is produced
- if they are not produced then we get female external genital development
genital tubercle-> clitoris
labio-scrotal swelling–> labia majora
uro-genital fold–> labia minora
when does the definitive signs of puberty begin for males and for females?
males-> 13.4 yrs (ejaculation)
females -> 12.9 yrs (menstrual bleed)
what hormone does the hypothalamus secrete ? and what does It do?
- GnRH
- produced in the arcuate nucleus (travels down the primary portal plexus)
- binds to GnRH R on gonadotrophs of APG
- stimulates release of gonadotrophins from the APG
- triggers gonadal activation via pulsatile GnRH secretion
- prolonged secretion leads to downregulation ofGnRH R on gonadotroph meaning less FSH/ LH release–> testes
what is responsible for this pulsatile release?
- Kisspeptin 1
- 54 aa NT
- `acts on KIss1R/ GPR54
- KISS1 expression rises at puberty
where does LH act ?
- produced by gonadotrophs
- acts on leydig, theca and granulosa cells
where does FSH act?
- produced by gonadotrophs
- acts on sertoli and granulosa cells
where does hCG act?
- produced by trophoblast cells
- acts on luteal cells (corpus luteum)
what is the same between both sexes and what differs?
- HP axis secretion is the same (FSH, LH)
- its the gonadal secretions that differ between sexes
male-> testis-> inhibit, T
female -> ovary-> oestrogen and progesterone
what determines the potency of sex steroids ?
- depends on how well they fit at the binding site of R
- some bind but don’t activate R (antagonists such as RU486) -> anti-P drug
- contraceptive pill-> P binds to other receptors too of same specificity s/e of acne
sex steroids can be grouped into 3 families of?
- derived from cholesterol
- progestogens–> pregnancy (placenta)
- androgens->maleness (adrenals)
- oestrogens -> femaleness ( liver, adrenals, adipose, placenta)
- all bind to intracellular nuclear steroid response elements
what do ovarian oestrogens do?
- induce growth of breasts and genitalia + axillary hair growth
testicular androgens ?
- growth go pubic, facial and axillary hair, genitalia, enlargement of larynx and laryngeal muscles–> lengthening and thickening of vocal cords
compare the difference of growth spurts between male and female
- girls grow 25cm
- girls grow 28cm
- boys begin 2 years later –> height take off is 10cm greater-> hence why males grow taller than females
- 24-36 average spurt length
what causes fusion of the epiphyseal growth plates?
- higher levels of oestrogen inhibiting GH-IGF-1 axis (late puberty)
- cartilage is replaced with bone
- during early puberty there are low levels of oestrogen –> more GH stimulates liver and chondrocytes too
