Embryology

Question 1

what is gastrulation

Answer 1

formation of the trilaminar disc- invagination of the epiblast cells through the primitive streak
ectoderm, mesoderm and endoderm

Question 2

what are the 3 groups of mesoderm

Answer 2

paraaxial (axis of body), intermediate and lateral plates

Question 3

what part of mesoderm forms the urogenital system

Answer 3

intermediate mesoderm

Question 4

when does gastrulation happen

Answer 4

week 3

Question 5

what common cavity do the urogenital system enter via the mesonephric duct

Answer 5

the cloaca (hindgut endoderm)

Question 6

what makes up the renal system in embryos

Answer 6

pronephrons - not functional
mesonephrons - produce urine, arent end stage kidney
metanephrons - form the kidneys, start low in pelvis then rise up

Question 7

what does the cloaca form

Answer 7

rectum, bladder and genitalia

Question 8

how is the indifferent gonad formed

Answer 8

primordial germ cells within yolk sac migrate via dorsal mesentary (via allatoic stalk) into intermediate mesoderm

stimulates body epithelium to proliferate and thicken to form the genital ridges. will also form somatic support cells which envelop the PGCs

this forms primitive sex cords

Question 9

what are somatic support cells

Answer 9

e.g. sertoli and follicular cells

Question 10

what do primdorial germs cells form

Answer 10

gametes

Question 11

what are the two primitive genital ducts

Answer 11

mesonephric (wollfian)

paramesonephric (mullerian)

Question 12

where do the mesonephric and paramesonephric ducts connect to

Answer 12

the posterior wall of the urogenital sinus

Question 13

when does sexual differentiation start to occur

Answer 13

week 7 onwards

Question 14

what triggers male development in an embyro

Answer 14

the presence of SRY (sex determining region of Y) transcription

Question 15

what do somatic support cells form in male development

Answer 15

develop into serotil cells which start to produce primary sex cords

Question 16

what do the primary sex cords from in males

Answer 16

testes and medullary cords - these engulf the PGCs

Question 17

what are the rete testes

Answer 17

connect the mesonephric tubules to the testis cords

Question 18

what is the tunica albguinae

Answer 18

thickened layer of connective tissue between the coelomic epithelium and the testis cord

Question 19

what is order of structures in the developing embryo testis

Answer 19

mesonephric duct- mesonephric tubules- retes testis- testis cords- tunica albuginea- epithelium

Question 20

in the developing testis there is an outer cortex and inner medulla, which of these degenerates

Answer 20

the cortex

Question 21

what is the function of sertoli cells in male development

Answer 21

secrete AMH (anti mullerian hormone) which causes the degeneration of the paramesonephric duct

stimulate gonadal ridge cells to form leydig cells (testosterone secreting).

• testosterone induces the formation of the epididymis, vas deferens and seminal vesicles.
• dihydrotestosterone (DHT) induces male specific external genitalia development and prostate

Question 22

what causes persistent mullerian duct syndrome and what does it result in

Answer 22

mutation of AMH or AMH receptor gene- mullerian (paramesonephric ducts fail to regress)

present with uterus, vagina and uterine tubes, testes in ovarian location, male external genitalia

Question 23

what fascilitates the descend of the testes

Answer 23

pulled caudally by the gubernaculum (on anterior body wall) through the inguinal canal

Question 24

where do the testes start before the descend

Answer 24

10th thoracic level

Question 25

what is cryptorchidism

Answer 25

failure of one/ both testes to descend

Question 26

what does the vaginal pouch of the parietal peritoneum allow

Answer 26

the testis to protract and move

Question 27

when and where do the male accessory glands start to form

Answer 27

sprout near the junction of the mesonephric duct and urethra during week 10

Question 28

what do the prostate and bulbourethral glands form from

Answer 28

endodermal invaginations from the urethra

Question 29

what do the seminal vesicles form from

Answer 29

outpouches form the mesonephric duct (intermediate mesoderm)

Question 30

what stimulates femal development of an embryo

Answer 30

the absence of the SRY transcription factor

Question 31

what do germ cells form in females

Answer 31

oogonia and then into primary oocytes

Question 32

what do somatic support cells form in females

Answer 32

granulosa cells which surround the primary oocytes

Question 33

what forms the primordial follicles in the ovary

Answer 33

the primary oocytes surrounded by the granulosa cells

Question 34

what stimulates the formation of granulosa cells from somatic support cells in female embryos

Answer 34

germ cells

Question 35

does the medulla or cortex of the indifferent gonad degenerate in females

Answer 35

the medulla degenerates- means you dont get ret testis/ connection to mesonephric duct

Question 36

why does the paramesonephric duct remain in females

Answer 36

as dont get AMH from serotli cells

Question 37

what is important about the anatomy of the paramesonepheric duct

Answer 37

is onto at top into peritoneal cavity

Question 38

what does the female gonad form

Answer 38

primaoridal follicles and thecal cells (leydig homonlog, increases oestrogen and progesterone)

Question 39

what does oestrogen stimulate in an embryo

Answer 39

formation of female external genitalia and development of paramesonephric ducts

Question 40

what do the paramesonephric ducts form

Answer 40

uterine tubes and fimbria uterus superior vagina

Question 41

what can remain in females of the mesonephric duct

Answer 41

epophoron and parophronon- not functional but can form cysts and adenomas

Question 42

what are the three parts of the paramesonephric duct

Answer 42

cranial (opens to coelomic cavity) horizontal (crosses mesonephrc duct) caudal (fuses with paramesonephric duct on the opposite side to make uterovaginal cavity)

Question 43

what is the uterovaginal canal

Answer 43

the fused caudal portion of the paramesonephric ducts create this= the uterus and superior vagina

Question 44

what is the vaginal lumen created

Answer 44

vacuolisation of the paramesonephric portion of the vagina and the sinuvaginal bulbs (this also produces the fornices)

Question 45

what cell origin make up vagina and cervix

Answer 45

bottom 2/3rds of vagina endoderm upper 1/3rd and cervix mesoderm

Question 46

what are female external genitalia distinguishable

Answer 46

after week 7

Question 47

what cell origin forms the glans and prepuce (foreskin)

Answer 47

ectoderm

Question 48

what is hypospadias

Answer 48

where external urethral opening lies in an abnormal position along the ventral aspect of the penis urine exits this cavity

Question 49

what does the genital tubercle form in both men and women

Answer 49

men- glans penis women- clitoris (these have same innervation and vascular supply)