Embryology: Fertilisation to Trilaminar

Question 1

during fertilisation what does sperm bind to

Answer 1

the zona pellucida glycoprotein (ZPG3)

Question 2

when sperm binds to ZPG3 what happens

Answer 2

it releases digestive enzymes form the sperm head and digests its way into the cell

Question 3

when the egg and sperm plasma membranes fuse what happens

Answer 3

sperm contents enter the egg

Question 4

sperm entry into egg triggers 2 things:

Answer 4

• completion of meiosis 2

- oocyte release of cortical granules

Question 5

function of cortical granules

Answer 5

kill off other sperm do avoid polyspermy

Question 6

during cleavage what happens

Answer 6

zygote undergoes mitotic division and subdivides the egg into smaller daughter cells

Question 7

what are the smaller daughter cells produced in cleavage called

Answer 7

blastomeres

Question 8

how many blastomere cells are totipotent

Answer 8

up to 8

Question 9

mosaicism

Answer 9

2+ cell lines with different chromosome complements

Question 10

mitotic non-disjunction

Answer 10

daughter cells have irregular chromosome numbers and can occur in early division of zygote

Question 11

what surrounds blastomeres

Answer 11

zona pellucida (ZP)

Question 12

how do cells in blastomeres maximise space

Answer 12

come in close contact with one another and form cell junctions

Question 13

what do outer cells in close contact with the zona pellucida form

Answer 13

extensive gap junctions

Question 14

when blastocysts form gap junctions with the ZP what enters

Answer 14

fluid through ZP

Question 15

what happens during blastocyst hatching

Answer 15

inner cell mass hatches out ZP leaving it behind and the embryo interacts directly with the endometrial lining for implantation

Question 16

embryoblast

Answer 16

inner cell mass of blastocysts that also consists of amnion and yolk sac

Question 17

when and where does implantation typically occur

Answer 17

day 6 on posterior/anterior uterine wall

Question 18

summarise week 1 of fertilisation

Answer 18

• day 1 - egg enters tube and is fertilised - DNA duplication begins
• day 3 - blastocyst enters uterus
• day 5.5-6 - implantation occurs

Question 19

when does the trophoblast divide

Answer 19

day 7.5

Question 20

what does the trophoblast divide into

Answer 20

• cytotrophoblast (inner layer)

- synctiotrophoblast (outer layer)

Question 21

what does the syncytiotrophoblast do

Answer 21

produce the human chorionic gonadotropin

Question 22

after trophoblast division what does the embryo do

Answer 22

organise into 2 cell layers and the amniotic cavity begins to form

Question 23

what two layers does the embryo first divide into and what surface do these form

Answer 23

• epiblast (dorsal)

- hypoblast (ventral)

Question 24

after the embryo divides into 2 layers, what 2 cavities begin to form and from which layer do they form from

Answer 24

• amniotic cavity (epiblast)

- primitive yolk sac (hypoblast)

Question 25

after the formation of the amniotic cavity and yolk sac what is complete on what day

Answer 25

implantation, day 9

Question 26

what closes off implantation

Answer 26

fibrin coagulum

Question 27

where and what forms lacunae

Answer 27

uniting vacuoles in the syncytiotrophoblast

Question 28

when is uteroplacental circulation established

Answer 28

day 12

Question 29

where does maternal blood flow into

Answer 29

lacunae

Question 30

on day 12 what develops (and eventually degenerates)

Answer 30

extraembryonic mesoderm

Question 31

what does the extraembryonic mesoderm form

Answer 31

chorionic cavity

Question 32

on day 13 what further develps

Answer 32

chorionic cavity, connecting stalk present

Question 33

what does the connecting stalk later develop into

Answer 33

umbilical cord

Question 34

what and when is the definitive (secondary) yolk sac formed

Answer 34

day 13, second wave of hypoblast cell migrate

Question 35

where is the amniotic cavity in relation to the bilaminar embryo and definitive yolk sac

Answer 35

above the bilaminar embryo disc and definitic yolk sac is underneath that

Question 36

where is the chorionic cavity once implantation is complete

Answer 36

surrounding the entire embryo

Question 37

where and when is the primitive streak formed

Answer 37

week 3, midline of caudal end of epiblast (amniotic cavity side)

Question 38

what forms the cranial and caudal ends of the primitive streak

Answer 38

• cranial-primitive pit and node

- caudal-primitive groove

Question 39

describe gastrulation

Answer 39

• epiblast cells move through the primitive streak forming 3 germ layers
• hypoblast cells are replacesd by endoderm
• cells migrating through the streak from the mesoderm
• epiblast cells become the ectoderm
• body axes established by primitive streak

Question 40

what is the fate of the ectoderm

Answer 40

• skin

- nervous system

Question 41

what is the fate of the overall mesoderm

Answer 41

divides into three layers either side of the notochord

Question 42

what are the three layers of the mesoderm

Answer 42

• paraxial mesoderm
• intermediate mesoderm
• lateral plate mesoderm (somatic)
• lateral plate mesoderm (visceral)

Question 43

fate of paraxial mesoderm

Answer 43

• axial skeleton, skeletal muscle and parts of dermis (back)

Question 44

fate of intermediate mesoderm

Answer 44

• urogenital systems and assoc. structures

Question 45

fate of lateral plate mesoderm (somatic)

Answer 45

• most of dermis, lining of body wall, parts of limbs

Question 46

fate of lateral plate mesoderm (visceral)

Answer 46

• CVS, mesothelial covering of organs, smooth muscle

Question 47

fate of endoderm

Answer 47

• lining of gut tube, resp tract, bladder and urethra