Sexual Differentiation Flashcards
male and female embryos contain duplicate sets of what?
genital ducts
the two sets of genital ducts in the embryo have the potential to become what
male or female internal genitalia
what determines whether an indifferent gonad develops into an ovary or testis
chromosomal content
development of embryonic structure into male and female reproductive organs and external genitalia depends on?
fetal hormone production
sex determination begins with what
commitment of the indifferent gonads to become testis or ovaries
sex chromosome complement of a person can be assessed how
maximum number of Barr bodies and fluorescent staining to detect Y-chromosomes
what gene is essential for promoting the differentiation of a biopotential gonad into testis
SRY (sex determining region on the y chromosome)
what are the pseudoautosomal regions of the Y chromosome
regions at the distal ends of the Y chromosome that are homologous to regions at the distal ends of the X chromosomes
where is the SRY gene located on the Y chromosome
close to the autosomal region on the short arm (p) of the Y chromosome
what sex chromosome is largest
X is much larger than Y
due to the size of the X chromosome what happens in each somatic cell of female embryos
one X is inactivated
what is an inactivated X called
Barr body
maximum number of barr bodies in a somatic diploid cell is equal to?
number of X chromosomes minus 1
the X chromosome from what parent is inactivated in female somatic cells
randomly occurs so 1/2 will have maternally-derived X chromosomes and 1/2 will have paternally-derived X chromosomes
what, if anything, escapes X inactivation
genes in pseudoautosomal regions of the X chromosomes
genital (gonadal) ridge
what is it
formed from epithelial and underlying mesenchymal cells proliferate making a thickened area along ventromedial surface of the mesonephros
primitive sex chords (what are they)
finger-like projections that proliferate from the epithelium into the underlying mesenchyme
(remains attached to epithelium during its early development)
genital (gonadal) ridge
when is it formed
5th week
form epithelium and underlying mesenchyme
before the 7th week gonads of both sexes are?
identical in appearance and referred to as indifferent gonads
indifferent gonad (parts)
external cortex
internal medulla
the precursor supporting cells of the indifferent embryo can differentiate into what
Sertoli Cells (XY embryo) Granolas Cells (XX embryo)
Primordial Germ Cells (PGCs)
where do they originate
outside the gonad
seen in yolk sac endoderm 3-4weeks post conception
Primordial Germ Cells (PGCs)
when and where do they migrate
5th week post conception
migrate from yolk sac ectoderm along dorsal mesentery of hindgut to the genital (gonadal) ridge
what happens to PGCs as they migrate
undergo cell division and extensive genetic reprogramming which involves the activation of genes and various epigenetic changes
what happens to PGCs as they enter developing genital (gonadal) ridge
rapidly surrounded by chords of somatic cells
Once surrounded by somatic cells PGCs commit to what
developmental pathway which leads them to become:
gonocytes (prespermatogonia)
oogonia
what determines the type of gonad the genial ridge will become
sex chromosomes present in somatic cells
what is the gene product of the SRY gene
a transcription factor
what is the major action of the transcription factor produced by SRY
SOX9 gene
SOX9 gene (what does it do where is it)
master regulator of Sertoli cell differentiation chromosome 17q (long arm)
in the formation of testis what differentiates and what regresses from the indifferent gonad
medulla differentiates
cortex regresses
in the formation of ovaries what differentiates and what regresses from the indifferent gonad
cortex differentiates
medulla regresses
what is the first discernible event of testis differentiation
appearance of Sertolic cells in medulla of indifferent gonad b/w 6-7 weeks of gestation
Stroll cells aggregate around what to form what
aggregate around gonocytes (PGCs of testis)
form testis cords
testis cords (what are they)
formed from Sertoli cells and gonocytes
precursors to seminiferous tubules
what happens to gonocytes within testis cords
enter mitotic arrest at 10-12 weeks
(most are differentiated in prespermatogonia
Leydig Cells (when and where do they appear)
functional leydig cells appear between developing seminiferous tubules b/w week 8 and 9
Sertoli Cells (what do they release)
paracrine factors that play a role in recruiting mesenchymal cells to developing testis
mesenchymal cells recruited to developing testis differentiate into what?
peritubular myoid cells
endothelial cells that form male-specific vasculature
Leydig cells
Lydia cells (what do they produce)
testosterone
Insulin-like 3(INSL-3)
seminiferous tubules can form in the absence of what
germ cells
meiosis of germ cells begins when in males
puberty
presence of more than one X with a Y does what
alters process of testicular development
Klinefelter Syndrome (cause)
47, XXY male
caused my meiotic nondisjunction
primitive sex cords later in development become what
tunica albuginea
primitive sex cords give rise to what
testis cords which become seminiferous tubules and rete testis of the mature testis
seminiferous tubules are what until puberty
solid
differentiation of ovary from indifferent gonad requires what
invasion of cortex by primordial germ cells
reactivation of the inactivated X chromosome in the germ cells
absence of SRY gene
When SRY absent but no germ cells or only one X what happen
ovary begins to differentiate but the developing ovary will regress
ovarian dysgenesis is associated with what
45, X karyotype
Turner Syndrome
PGCs that migrate to presumptive ovary do what
proliferate rapidly and differentiate into oogonia
what happens to some oogonia in about 11 weeks gestation
leave pool of proliferating cells and enter into meiosis
oogonia that leave pool and enter meiosis are known as what
primary oocytes
meiosis of primary oocytes is arrested when
prophase of first meiotic division
what happens to other oogonia with the onset of oogonial meiosis
atresia (form of programed cell death)
primordial follicles (when do they arise)
week 13
primordial follicles (how are they formed)
arise a pregranulosa cells aggregate to form a single layer of cells around the primitive oocyte
number of germ cells in ovary peaks when and then what happens
20 weeks and then declines
what leads to the decline in number go female germ cells after week 20
decrease in rate of oogonial mitosis
the atresia of oogonia that are not incorporated into follicles
the atresia of follicles that start to mature
what happens to follicles that mature in utero
interrupted by follicular atresia
all of primordial follicles that a woman will have are formed when?
by the time an infant is 6 months old
seminiferous tubules develop when in gestation
6-7 weeks in
leydig cells develop and secrete testosterone when in gestation
8-9 weeks
oogenesis begins when in gestation
11-12 weeks
formation of primordial follicles happens when in gestation
13 weeks
preantral follicles are present when in gestation
26 weeks
in developing ovary what happens to primitive sex cords
grow into medulla and degenerate
cortical cords (what are they)
represent a second wave or cord formation that occurs during week 7
extend from surface epithelium into the underlying mesenchyme
as the cortical cords increase in size what happens to them
PGCs are incorporated into them
after week 13 (about week 16) the cortical cords begin to break up into what
distinct cell clusters (primordial follicles)
primordial follicles consist of what kinds of cells
primary oocyte surrounded by a single layer of pregranulosa cells
each follicle is surrounded by a basal lamina
what are the two sets of genital ducts
mesonephric or wolffian ducts
paramesonephric or mullerian ducts
both genital ducts empty into where
urogenital sinus
wolffian ducts differentiate into what
epididymis
vas deferens
seminal vesicles
ejaculatory ducts
mullerian ducts differentiate into
fallopian tubes
uterus
cervix
upper third of vagina
mullerian ducts (describe shape)
cranial end is funnel-shaped and opens into peritoneal cavity
caudal end fuse to form uterovaginal primordium
uterovaginal primordium (how is it formed)
fusion of caudal end of mullein ducts
differentiation of male internal genital tract involves what
mullerian duct regression and wolffian duct development
differentiation of male internal genital tract requires what
hormones produced by the fetal testes
anti-mullerian hormone (AMH)
where is it released, what does it do
released by sertoli cells
induces apoptosis of mullerian ducts
AMH induced mullerian duct regression occurs when
weeks 7-10
AMH induced mullerian duct regression (what is special about it after week 8)
time sensitive
ducts are non responsive after week 8
what stimulates testosterone production by the fetal testes
chorionic gonadotropin (hCG)
wolffian duct differentiation begins when and in response to what
week 9
testosterone produced by fetal leydig cells
differentiation of genital ducts along female lines occurs how (in relation to hormones)
absence of hormone stimulation
what happens to wolffian ducts w/o testosterone
destabilize and undergo regression
syndrome of persistent mullein ducts (what is it/cause)
rare condition that can occur when a normal genotypic and phenotypic male cannot synthesize AMH or has defective AMH receptor
syndrome of persistent mullein ducts (symptoms)
testes dont descend
mullerian duct derivatives (fallopian tubes, uterus, cervix, upper 1/3 of vagina) persist but underdeveloped
what are the undifferentiated external genitalia
genital tubercle
genital fold
labioscrotal swelling
differentiation of indifferent external genital structures of the embryo along male lines requires what
dihydrotestosterone (DHT)
dihydrotestosterone (DHT) is formed how
derived from testosterone using 5-alpha reductase
absence of androgen stimulation what happens to external genitalia
develop along female lines
the genital tubercle gives rise to what structures
glans penis or clitoris
genital swelling gives rise to what
labia majora or scrotum
genital folds form what
vental folds of the penis
labia minora
urogenital sinus becomes what in males and when
prostatic buds develop by week 10
urogenital sinus becomes what in females
lower part of vagina from walls of sinus
what effect do female sex hormones have on differentiation of urogenital sinus and external genitalia
none
what effect do female sex hormones have on differentiation of internal genitalia
none
Syndrome of complete androgen resistance (what is it)
testes capable of secreting androgens will be present in the abdominal cavity
Syndrome of complete androgen resistance (symptoms)
both male and female internal genitalia are absent
external genitalia and secondary sexual characteristics are female
pubic hair will be scant or absent
5-alpha-reductase deficiency
internal genitalia will develop along male lines and the external genitalia will be ambiguous due to incomplete masculinization
child may be mistaken for female at birth
further masculinization of external genitalia will occur at puberty
excessive amounts of androgens in utero to a 46, XX embryo does what
virilization of the external genital
if exposure after 12 weeks- clitoral hypertrophy
Insulins-Like peptide 3 (INSL 3)
what is it where is it produced
leydig cells
linked to transabdominal phase of testicular descent
cryptorchidism (what is it)
failure of descent of one or more testis
scrotal descent happens when
b/w weeks 25-32
what two hormones play a role in testicular descent
INSL 3
Testosterone
(both from leydig cells)
