Reproductive tract differentiation and development

Question 1

precursor of gametes

Answer 1

primordial germ cell

Question 2

germ cell definition

Answer 2

any biological cell that gives rise to the gametes of an organism that reproduces sexually

Question 3

where do germ cells originate in animals?

Answer 3

primitive streak

Question 4

primordial germ cell definition

Answer 4

cells that originate from totipotent cells of the cleaved blastula that will give rise to gametes and are yet to reach the gonads

Question 5

what happens to the primordial germ cells once they are formed?

Answer 5

begin to migrate 6.25 days after conception

migrate to the embryonic endoderm and then to the hindgut and finally towards the genital ridges where the somatic gonadal precursors reside

Question 6

gonadal ridge definition

Answer 6

somatic cells that are the precursor to the gonads

Question 7

which chromosome is important in sex determination?

Answer 7

Y chromosome

Question 8

which region on the Y chromosome is especially important?

Answer 8

SRY

Question 9

SRY function

Answer 9

directs male development in mammals by inducing somatic cells of the gonadal ridge to develop into testis rather than an ovary

codes for a DNA binding protein that is involved in testes development

influences cells to become sertoli cells

Question 10

sertoli cell function

Answer 10

stimulate arriving primordial cells to differentiate into sperm. lack of SRY results in the differentiation of eggs

Question 11

what is the sex of the baby dependent on?

Answer 11

the two sex chromosomes, XY will be male and XX female

the sperm can either bring a Y or X chromosome

Question 12

SRY synonym

Answer 12

sex-determining region of the Y chromosomes

Question 13

how can an XY individual be female?

Answer 13

express DAX-1 gene which is an anti testes factor

Question 14

where do the gonads develop from?

Answer 14

gonadal ridge of intermediate mesoderm

mesenchyme of mesonephric origin

Question 15

first stage of gonadal development and genes involved

Answer 15

form on the medial aspect of the intermediate mesoderm in the region of the mesonephros

WT1- Wilms Tumour= kidney and gonad formation

SF1- steroidogenic factor- failure of adrenal gland and gonadal formation

LHX9- formation of gonadal ridge

Question 16

stages of gonadal ridge development

Answer 16

1. gonadal ridge from mesonephros descends within the abdomen
2. germ cells migrate into the gonadal ridge
3. germ cells develop in epiblast and migrate to the gonadal ridge via the yolk sac and hind gut (cell surface molecules required for migration)

Question 17

male germ cell migration

Answer 17

1. primordial germ cells differentiate into primitive sex cords
2. sex cords proliferate by mitosis and surround the primordial germ cells to form testis cords (seminiferous tubules) by action of testis-determining factor
3. cells surrounding the primordial gem cells differentiate into sertoli cells due to SRY
4. primordial germ cells concentrated in medulla, cortex regresses
5. medullary cord develops and contain spermatogonia, sertoli cells
6. network of tubules fuse to create the seminineforous tubules and become connected to outgrowths from the medonephros via the rete testis
7. leydig cells form and secrete testosterone

Question 18

female germ cell migration

Answer 18

1. sex cords dissociate, primordial germ cells are in nests. Produce cortical cords instead that break down. . Immature ova originate from cells from the dorsal endoderm of the yolk sac
2. germ cells form individual primordial follicles
3. meiosis commences then arrests in fetus
4. primordial follicles start to develop but undergo atresia- apoptosis until puberty
5. primordial follicles concentrate in cortex, medulla degenerates
6. oogonia proliferate

Question 19

when do the primordial germ cells begin to change relative to sex?

Answer 19

prior to their occupation in genital ridge there is no known difference between XX and XYs

once migration is complete and germ cell determination has occurred

Question 20

first stage of forming internal genitalia name

Answer 20

indifferent stage

Question 21

what pairs of ducts are present in embryos + where

Answer 21

Mesonephric (Wolffian) ducts

Paramesonephric (Mullerian) ducts

both ends of the cloaca

Question 22

male formation of internal genitalia

Answer 22

1. Testosterone produced by Leydig cells
2. Presence of testosterone allows mesonephric ducts to develop to form the primary male genital ducts - give rise to the efferent ductules, epididymis, vans deferens, seminal vesicles
3. Sertoli cells produce anti-Mullerian hormone which results in the paramesonephric ducts degenerating. Appendix testis remnant remains

Question 23

male formation of internal genitalia

Answer 23

1. absence of Leydig cells, no testosterone, Wolffian ducts degenerate- leaving Gartner’s duct
2. absence of anti-Mullerian hormone also allows development of the paramesonephric ducts

Question 24

different regions of the Mullerian duct + what forms

Answer 24

cranial- fallopian tubes

horizontal- fallopian tubes

caudal- fuses to form uterus, cervic, upper 1/3 of vagina

Question 25

what forms the lower 2/3 of vagina?

Answer 25

sinovaginal bulbs, derived from pelvic part of urogenital sinus

Question 26

indifferent stage of external genitalia formation

Answer 26

begins in the third week

1. mesenchymal cells from the primitive streak migrate to the cloacal membrane to form a pair of cloacal folds
2. cranially the cloacal folds fuse to make the genital tubercle
3. caudally they divide into urethral folds anteriorly and anal folds posteriorly
4. genital swellings develop on either side of the urethral folds

Question 27

male external genitalia formation

Answer 27

1. rapid elongation of the genital tubercle, which becomes the phallus
2. urethral folds are pulled to form the urethral groove, extending along the caudal aspect of the phallus
3. folds close over by the 4th month forming the penile urethra
4. genital swellings become the scrotal swellings, moving caudally to form the scrotum

Question 28

what is the development of the external male genitalia driven by?

Answer 28

androgen from the testes dihydrotestosterone DHT

Question 29

female external genitalia formation

Answer 29

1. genital tubercle elongates slightly to form the clitoris
2. urethral folds and genital swellings do not fuse. Urethral folds form the labia minora and genital swellings form the labia majora
3. urogenital groove remains open, forming the vestibule into which the urethra and vagina open

Question 30

what is the development of external female genitalia driven by?

Answer 30

oestrogen

Question 31

where do the gonads arise?

Answer 31

upper lumbar region

Question 32

what are they tethered to + how?

Answer 32

testes to scrotum and ovaries to labia by the gubernaculum

Question 33

descent of testes

Answer 33

1. as the body of fetus grows, the testes become more caudal

2. pass through inguinal canal around 28th week and reach scrotum at 33rd week

Question 34

descent of ovaries

Answer 34

1. migrate caudally in a similar fashion to testes from their origin on the posterior abdominal wall
2. reach final position in true pelvis

Question 35

male and female remnants of the gubernaculum

Answer 35

scrotal ligament

ovarian ligament and round ligament of uterus