Embryology Ch 2 and 3 9-2

Question 1

Embryo week 2

Answer 1

Week of 2s. Lots of cavities, layers, becoming a bilaminar disc. Implantation finished. Trophoblast differentiates into two layers, embryoblast forms 2 layers (hypoblast and then some), extraembryonic mesoderm splits into 2 layers, 2 cavities form -amniotic and choreic cavity.

Question 2

Embryo week 3

Answer 2

Focus on beginning to form body axis of embryo (notochord, primitive streak, become trilaminar disc).

Question 3

Trophoblast differentiated

Answer 3

Day 7 or day 8 - cytotrophoblast and syncitiotrophoblast. form.

Question 4

Embryoblast differentiates

Answer 4

Day 8 - hypoblast and epiblast. Flat cells along interior base form hypoblast (primary endoderm). Epiblast stay where it is (near cytotrophoblast).

Question 5

Epiblast

Answer 5

Hugely important - all 3 of primary tissue layers originate from this layer. Endoderm, ectoderm, mesoderm.

Question 6

Hypoblast

Answer 6

Flat cells along interior base (primary endoderm).

Question 7

Amniotic cavity

Answer 7

Within epiblast region. This forms day 8. Amnioblasts are epiblast cells adjacent to cytotrophoblast. This occurs at the same time as the creation of the difference between epiblast and hypoblast layers.

Question 8

Amnioblast

Answer 8

Epiblast cells that push outwards to form amniotic cavity. Just adjacent to cytotrophoblast.

Question 9

Day 9

Answer 9

Fully implanted (little fibrin coagulum plugs the cell in - sealing it essentially).

Question 10

Exocoelomic (heuser) membrane

Answer 10

Hypoblast cells are displaced along cytotrophoblasts, forms a lining of exocoelomic cavity (primitive yolk sac, primary umbilical vessicle).

Question 11

Fibrin coagulum

Answer 11

Fills in tiny space in endometrial wall. Day 9 Happens in syncitial layer. Fibrin coagulum (connective tissue/scar), within external syncitial layer there are tiny decayed spots that forms Lacunae.

Question 12

Vacuoles

Answer 12

Appear in syncytium of embryonic pole.

Question 13

Lacunae

Answer 13

Small holes/pits, important for developing blood flow.

Question 14

Lacunar stage

Answer 14

Begin to form vacuoles (see slides)

Question 15

Day 11 and 12

Answer 15

Trophoblast characterized by lacunar spaces in the syncytium, Forms intercommunicating network.
Cells of syncytiotrophoblast erode endothelial lining of maternal capillaries. Setting up distribution for nutrients.

Question 16

Syncytial Lacunae

Answer 16

become continuous with sinusoids. Establishes uteroplacental circulation.

Question 17

Sinusoids

Answer 17

**

Question 18

Extraembryonic mesoderm

Answer 18

Form extra-embryonic structures, New cells appear between inner surface of cytotrophoblast and outer surface of exocoelomic cavity. As you form this, you get tiny fluid filled spaces. Known as Extraembryonic fluid filled spaces which come together to form a new cavity.

Question 19

Extraembryonic cavity

Answer 19

Coreonic cavity - tiny spaces form giant corionic cavity. As this forms, there is distinct mesoderm that surrounds lining of cytotrophoblasts and amnion, this is the extraembryonic somatic mesoderm. Day 11-12

Question 20

Extraembryonic somatic mesoderm

Answer 20

Lines inner lining of cytotrophoblasts and amnion.

Question 21

Extraembryonic splanchnic mesoderm

Answer 21

Lines yolk sac, is exposed to extraembryonic cavity.

Question 22

Connecting stalk

Answer 22

Connects yolk sac and amniotic cavity to endometrium.

Question 23

Day 13 **listen to this slide

Answer 23

Cytotrophoblasts are still out there, most of the syncitial layer is gone, and primary villi … Hypoblast produces cells that form secondary yolk sac (definitive yolk sac)

Question 24

Secondary Yolk Sac

Answer 24

Definitive yolk sac. Exocoelemic cysts in the extraembryonic coelom (chorionic cavity).

Question 25

Chorionic cavity forms

Answer 25

Day 13 - extraembryonic mesoderm lining the inside of cytotrophoblast. This is known as the chorionic plate

Question 26

Chorionic plate

Answer 26

extraembryonic mesoderm lining the inside of cytotrophoblast. Important in the extablishment of the connecting stalk and develops into extraembryonic structures. *does not include stalk

Question 27

Connecting stalk

Answer 27

Will develop into the umbilical cord with development of blood vessels.

Question 28

Prechordal plate

Answer 28

If you look at what will become the embryo on cross-section, you see tight fusion between hypoblast and epiblast. There are columnar cells, and these cells along with the general area will become the oral cavity.

Question 29

Recap of week 2

Answer 29

Implantation finished, uteroplacental ciruclation established via lacunae blood vessels. Embryoblast forms bilaminar disc, amniotic and chorionic cavities form. Extraembryonic mesoderm forms - somatic (amniotic sac) and splanctic (yolk sac), primary and secondary yolk sacs.

Question 30

Week 3

Answer 30

Formation of primitive streak and node (leads to gastrulation). Gastrulation occurs- which forms 3 primary tissue layers. All 3 originate from epiblast. Formation of notochord occurs (solid rod that runs dorsal to embryo that is important for nervous system - provides axis). Embryo also grows significantly.

Question 31

Gastrulation

Answer 31

Formation of 3 layers - ectoderm, mesoderm, endoderm. All layers formed from epiblast. Begins with formation of primitive streak. Starts with swellings in epiblast.

Question 32

Primitive streak

Answer 32

Raised ridge towards posterior grows towards cranial end. This ridge is the streak. Two ridges with a groove. Occurs in epiblast as cells start to move. This will continue to grow cranially (to prechordal plate/oropharyngeal membrane). Will ahve distinct cephalic end (primitive node) which surrounds the primitive pit.

Question 33

Oropharyngeal membrane

Answer 33

Will become mouth

Question 34

Primitive pit

Answer 34

Where cells will move their way under the surface towards the hypoblast. Moves. Detach cells from epiblast, move down into pit or groove.

Question 35

Invagination

Answer 35

Epiblast cells that go down into hypoblast that displace and replace hypoblast. This forms definitive endoderm. Those that lie between epiblast and endoderm will become mesoderm. Cells that do not detach and migrate remain in epiblast to form ectoderm.

Question 36

Gastrulation

Answer 36

Cells continue to move laterally and cranially. In cephalic diretion, cells pass on each side of prechordal plate. Now a trilaminar disc.

Question 37

Prechordal plate

Answer 37

Formed between tip of notochord and oropharyngeal membrane.

Question 38

Notochord formation

Answer 38

Occurs w/gastrulation. Acts as rod that creates the backbone to the formation of the nervous system. Grows until prechordal plate, then once it hits that plate, the structure starts to acquire a lumen.

Question 39

Prenotochordal cells

Answer 39

invaginate in the primitive pit. Instead of forming primary tissue layers, forms notochordal process. This process pushes forward to prechordal plate. This also helps push everything to prechordal plate.

Question 40

Notochordal canal

Answer 40

Lumen in notochord that occurs once it hits the prechordal plate.

Question 41

Notochordal process

Answer 41

floor fuses with endoderm below and it degernates. Notochordal process is close to developing endoderm. Once it fuses, it degerates, leading to opening between amnionic cavity and umbilical vesicle.

Question 42

Neurenteric canal

Answer 42

Canal between amnionic cavity and umbilical vesicle - very brief. You need to look at images for this.

Question 43

Notochordal plate

Answer 43

Remains of notochordal process after formation of neurenteric canal. Rises back up off of endoderm. As it does this it separates to form notochord.

Question 44

Notochord

Answer 44

Initially a single rod - not hollow. Forms all of intervertebral discs.

Question 45

Cloacal Membrane

Answer 45

Formed at caudal end of embryonic disc. Similar to oropharyngeal membrane. Yolk sac forms diverticulum that extends into connecting stalk. Allantois forms around day 16. *Will eventually form anus.

Question 46

Allantois

Answer 46

Not any real function in developing humans (have more of a play in orgs. that develop in eggs). Forms around day 16 caudally.

Question 47

Due to primitive streak, we’ve established

Answer 47

Body axis. (primitive streak forms caudally to cranially, you also have a right and left side, and on a sagittal section you can figure this out as well).

Question 48

Beginning of week 3 trophoblast

Answer 48

Further develops - characterized by primary villi. Primary villi nothing more than cytotrophoblastic core covered by syncytial layer. Once blood comes here, mesoderm penetrates core of villi.

Question 49

Secondary villus

Answer 49

Has extra-embryonic mesodermal core (different from others), covered by cytotrophoblast and then syncytio…. End of week 3, these mesodermal c ells differentiate into bloodcells and small blood vessels. These form…

Question 50

Tertiary villus

Answer 50

Core of mesoderm, blood islands within it, cytotrophoblast, syncytio, etc. Will form blood connection in and will have a play in umbilical cord development. Does this through vasculogenesis

Question 51

Vasculogenesis

Answer 51

Blood vessels arise from blood islands. Hemangioblasts accumulate and form vessels.

Question 52

Angiogenesis

Answer 52

Blood vessels sprouting from existing vessels.

Question 53

Further trophoblast development

Answer 53

Capillaries in tertiary villi make contact with capillaries developing in extra-embryonic mesoderm of chorionic plate and in connecting stalk THIS IS OUTSIDE OF THE EMBRYO. Choreonic plate = extra-embryonic mesoderm. Choreonic cavity enlarges, embryo attaches to trophoblastic cell by connecting stalk.

Question 54

Intraembryonic circulatory system

Answer 54

Connecting the placenta and the embryo

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