sexual differentiation

Question 1

chromosomal sex

Answer 1

importance of the Y chromosome in mammalian sex differentiation

Question 2

gonadal sex

Answer 2

development of the gonadal rise of intermediate mesoderm, origins and migrations of primordial germ cells

Question 3

phenotypic sex

Answer 3

development of internal and external genitalia

Question 4

gonadal ridge formation

Answer 4

forms on the medial aspect of the intermediate mesoderm in the region of the mesonephros
around week 5

Question 5

important genes in gonadal ridge formation

Answer 5

WT1 (kidney and gonads)
SF1
LHX9
all act upstream of SRY

Question 6

what occurs as the ridge descends through abdomen

Answer 6

concentration of ridge

testis or ovary forms from undifferentiated gonad

Question 7

gene required for testis function

Answer 7

SRY/SOX9 from Y chromosome

lack causes ovary formation

Question 8

germ cell migration

Answer 8

successful migration of germ cells into gonadal ridge important for ultimate functioning gonad
mis-directed primordial germ cells may develop into teratomas

Question 9

where do germ cells develop

Answer 9

develop in epiblast and migrate to the gonadal ridge via the yolk sac and hind gut

Question 10

what are the germ cells associated with

Answer 10

primitive sex cords - tissue of the gonadal ridge

Question 11

primitive sex cords in males

Answer 11

sex cord cells proliferate by mitosis and surrounded the primordial germ cells to form testis cords
cells surrounding the germ cells differentiate into sertoli cells initiated by SRY
primordial germ cells called the prospermatogonia

Question 12

primitive sex cords in female s

Answer 12

sec cords dissociate so the primordial germ cells are in ‘nests’ (primordial follicles). meiosis commences then arrests in foetus, follicles start to develop but undergo atresia until puberty

Question 13

gonadal development in males

Answer 13

primordial cells concentrate in medulla, cortex regresses
medullary cords develop and contain spermatogonia and Sertoli cells -> seminiferous tubules and rete testes
leydig cells form and secrete testosterone

Question 14

gonadal development in females

Answer 14

primordial follicles concentrate in the cortex of the developing ovary, medulla degenerates
cortex of indifferent gonads form ingrowths = cortical cords
oogonia proliferation

Question 15

internal genitalia form from

Answer 15

mullerian (paramesonephric) ducts and wolffian (mesonephric) ducts

Question 16

fate of ducts in females

Answer 16

mullerian duct maintained, forms the uterine tubes, uterus and upper part of vagina
wolffian ducts degenerate
wnt 4 importnat

Question 17

fate of ducts in males

Answer 17

wolffian ducts differentiate to form the epididymus, vas deferens and seminal vesicles
prostate glands from urogenital sinus
mullerian duct degenerates
needs testosterone

Question 18

what do Sertoli cells secrete to cause this duct differentiation

Answer 18

mullerian inhibiting substance

causes the mullerian ducts to regress

Question 19

indifferent stage of external genitalia development

Answer 19

up to 8th week
genital tubercle -> phallus or clitoris
genital swelling -> scrotum or labia majora

Question 20

male external development occurs when

Answer 20

androgens are produced from leydig cells

Question 21

female external development occurs when

Answer 21

presence of ovary or lack of gonad

Question 22

what is required to masculinise external genitalia

Answer 22

testosterone converted to dihydrotestosterone

converted by 5 alpha reductase in leydig cells

Question 23

descent of testes

Answer 23

descent into scrotum

trans-abdominal, passing through inguinal canal

Question 24

chemicals important for testicular descent

Answer 24

testosterone
DHT
mullerian inhibiting factor
members of hox gene family

Question 25

wolffian duct in females

Answer 25

lack of testosterone causes complete duct regression

Question 26

what is the gubernaculum

Answer 26

embryonic structure
aids the descent of the gonads
mesenchymal cord
between the caudal end of testis and scrotum