A3. 1st three weeks of development

Question 1

What is the embryonic phase?

Answer 1

First 8 weeks of development - considered embryo

Question 2

zygote

Answer 2

when nucleus of sperm and nucleus of egg fuse

first time it has full 46 chromosomes

Question 3

blastomere

Answer 3

when zygote divides - two daughter cells are blastomeres

division is slow process - takes 24 hours

product is two daughter cells with 46 chromosomes each

Question 4

zona pellucida

Answer 4

proteoglycan “shell”

Question 5

Morula

Answer 5

~16 cell phase

some start heading towards periphery, some in middle

cells around periphery start to connect through tight junctions

Question 6

blastocyst

Answer 6

cells around periphery are taking fluid and pushing it towards the middle

creates ring around edge, and inner cell mass - process called compaction

this takes place in the uterus (everything before was near the fallopian tubes)

Question 7

late blastocyst

Answer 7

zona pellucida disappears

fluid space becomes larger and stretches the periphery cells out

outer cells = trophoblast

inner cell mass = embryo

Question 8

trophoblast

Answer 8

outer cells of late blastocyst

Question 9

endometrium

Answer 9

epithelial wall of uterus

Question 10

implantation

Answer 10

trophoblast edge where inner cells are “kisses” endometrium and attaches

Question 11

syncytium

Answer 11

cytotrophoblasts that made contact with uterine wall divide and form a new layer

Question 12

syncytiotrophoblasts

Answer 12

secrete enzymes that break down ECM of endometrium allowing implantation of embryo

Question 13

hypoblast

Answer 13

cells facing blastocyst become simple cuboidal

Question 14

epiblast

Answer 14

cells facing cytotrophoblasts become columnar

Question 15

amniotic cavity

Answer 15

forms between epi hypoblast and epiblast, and eventually epiblast completely surrounds the amniotic cavity

Question 16

amnioblast

Answer 16

previously epiblast, becomes amnioblast once they surround the amniotic cavity

Question 17

trophoblastic lacuna

Answer 17

empty space in the syncytiotrophoblast

filled by maternal blood

Question 18

heuser’s membrane

Answer 18

probably comes from hypoblast - surrounds cavity

Question 19

primary yolk sac

Answer 19

develops from cavity and is surrounded by heuser’s membrane

Question 20

extraembryonic reticulum

Answer 20

like ECM with fibers

cushion

Question 21

extraembryonic mesoderm

Answer 21

formed by peripheral cells from embryonic mass

mesoderm migrates around to completely cover heusers membrance and the cytotrophoblast

Question 22

chorion

Answer 22

completely surrounds embryo and is lined by extraembryonic mesoderm on all sides

Question 23

primary stem villi

Answer 23

little plugs of cytotrophoblast that invade the syncytiotrophoblast and get close to the maternal blood supply

Question 24

definitive yolk sac

Answer 24

formed when cells lining yolk sac invaginate and pinch off a remnant of the primary yolk sac

Question 25

secondary stem villi

Answer 25

replace primary stem villi

Question 26

connecting stalk

Answer 26

extraembryonic mesoderm holding embryonic mass to uterine wall

will eventually become umbilical cord

Question 27

buccopharyngeal and cloacal membranes

Answer 27

where there will be no mesenchyme/mesoderm between epiderm and endoderm

Question 28

primitive streak

Answer 28

in epiblast - primitive pit and primitive groove

Question 29

gastrulation

Answer 29

process of producing middle mesenchyme layer between epiblast and hypoblast

3 primary germ layers

Question 30

notochordal process

Answer 30

region of mesoderm which migrates up along the axis

Question 31

neurulation

Answer 31

notochord induces ectoderm to form a neural plate

Question 32

bilaminar embryonic disk

Answer 32

hypoblast and epiblast