Lecture 4 - Early Embryogenesis

Question 1

when does cleavage of the zygote happen

Answer 1

mitotic division happens rapidly at 30 hours after fertilization

Question 2

What day?

12 -32 blastomeres (=morula)
inner cell mass (embryoblast) surrounded by layer of flattened cells (trophoblast)

Answer 2

Day 3

Question 3

trophoblast secretes

Answer 3

early pregnancy factor

Question 4

What day?

morula is now called blastocyst

blastocystic cavity forms

Answer 4

Day 4

Question 5

outer cells that give rise to the embryonic part of the placenta

Answer 5

trophoblast

Question 6

cells that form the embryo

Answer 6

embryoblast

Question 7

What day?

blastocyst travels in uterine fluid and sheds zona pellucida

Answer 7

Day 5-6

Question 8

what day?

blastocyst attaches to endometrial lining
trophoblast differentiates into two layers

Answer 8

Day 6

Question 9

trophoblast differentiates into (2)

Answer 9

cytotrophoblast - inner layer of cells

synctiotrophoblast - outer layer of cells that extends into endometrial epithelium and allows the blastocyst to “burrow” in

Question 10

synctiotrophoblast secretes

Answer 10

Human chorionic gonadotropin (hCG)

Question 11

What happens in week 2? (4 things)

Answer 11

blastocyst implants

formation of embryonic disc

formation of amniotic cavity

trophoblast continues to differentiate

Question 12

week 2: embryoblast forms embryonic disc, which consists of (2)

Answer 12

epiblast - thicker layer that forms floor by amniotic cavity

hypoblast - thinner layer, continuous with the primordial umbilical vesicle

Question 13

what is the exocoelemic membrane?

Answer 13

forms to make the primary umbilical vesicle and surrounds the blastocystic cavity

Question 14

________ cavity is on top of developing embryo and

________ cavity is below

Answer 14

amniotic

blastocystic

Question 15

what is the amnion

Answer 15

thin, transparent, nonvascular cavity

formed by aminogenic cells, maternal blood, and fetal kidneys

Question 16

functions of amnion (3)

Answer 16

protective cushion
temperature
free movement

Question 17

what day?

embryo completely embedded in endometrium
closing plug forms
endometrial wall regenerates, covering the plug

Answer 17

Day 10

Question 18

what is the chorion?

Answer 18

the outermost membrane surrounding the embryo

Question 19

what do the chorionic villi do?

Answer 19

extract nutrients from maternal blood and endometrial tissue

Question 20

when do primary chorionic villi appear?

Answer 20

end of week 2

Question 21

What happens in week 3? (3 general things)

Answer 21

gastrulation - differentiation of 3 germ layers

development of notochord

Allantois and chorionic villi formation

Question 22

Define:

primitive streak

primitive groove

primitive node

primitive pit

Answer 22

streak - cells migrate to dorsal caudal location and elongate by adding more cells

groove - small depression in primitive streak

node - cluster of cells at cranial end of primitive streak

pit - deepest part of primitive groove

Question 23

cells leave the primitive streak to form _____

Answer 23

mesenchyme

Question 24

what is a sacrococcygeal teratoma

Answer 24

remnants of primitive streak persist

- tumor has tissues from all 3 germ layers at different points of formation

Question 25

Inductions for gastrulation

Answer 25

growth factors and signaling from cells, coordinate factors with genes, cell interactions, proliferation of cells, and apoptosis

Question 26

where does notochordal process begin to form?

Answer 26

deep to the primitive pit

Question 27

notochordal process (with notochordal canal) extends cranially to _______ ________

Answer 27

prechordal plate

Question 28

cellular rod formed from axial mesoderm that creates the axis of the embryo, is a template for development of bones of the head and vertebral column, is site of vertebral bodies, and forms the neural plate

Answer 28

notochord

Question 29

define neural plate (general)

Answer 29

primordial CNS

Question 30

notochord degenerates and forms the _____

Answer 30

nucleus pulposus of IV discs

Question 31

describe development of neural tube (day 18)

Answer 31

central axis of neural plate invaginates and forms the neural GROOVE with neural FOLDS. The FOLDS then fuse together to form the the neural TUBE which separates from the ectoderm

Question 32

what do neural crest cells do

Answer 32

separate from the neural tube as it's developing, and begin to lay framework for PNS

Question 33

name 2 neural tube defects

Answer 33

spina bifida | anencephaly

Question 34

what are somites

Answer 34

surface elevations in paraxial mesoderm form axial skeleton, muscle, and some skin

Question 35

transcription factors involved in the development of somites (2)

Answer 35

Fox C1 and C2 | Delta-Notch

Question 36

The allantois develops from the ________ and is the basis of ___________ and __________

Answer 36

umbilical vesicle early blood formation urinary bladder

Question 37

main exchange site of material between embryo and maternal blood

Answer 37

chorionic villi

Question 38

brings primordium of brain above heart and oropharyngeal membrane

Answer 38

head fold

Question 39

brings tail region over cloacal membrane, umbilical cord is brought ventrally

Answer 39

tail fold

Question 40

brings edges of embryonic disc ventrally forming a cylindrical embryo

Answer 40

lateral fold

Question 41

________ is brought ventrally and fuses with _______ to form umbilical cord

Answer 41

connecting stalk umbilical vesicle

Question 42

when does folding happen? (week)

Answer 42

Week 4

Question 43

what appears in week 4? (6)

Answer 43

``` pharyngeal arches upper limb buds lower limb buds otic pits - future internal ears lens placodes - future lenses rudimentary cardiovascular system ```

Question 44

Highlights of week 5 (2)

Answer 44

Growth of head rapidly increases | mesophrenic ridges - future kidneys

Question 45

Highlights of week 6 (3)

Answer 45

twitching digital rays - digits auricular hillocks - auricle of ear

Question 46

Highlights of week 7 (1)

Answer 46

Hand plates - notches separate future digits

Question 47

Highlights of week 8 (6)

Answer 47

digits separated, but webbed eyelids close hands and feet grow towards each other ventrally head is disproportionately large primary ossification centers begin to form sex differences begin