Ben's Embryology

Question 1

What 2 cell types do the trophoblasts differentiate into?

Answer 1

cytotrophoblasts - surround bilaminar disc

**syncitiotrophoblasts **- a fusion of neighboring tblasts which invade into the decidua

Question 2

What do the embryoblasts form after implantation?

Answer 2

bilaminar disc

Question 3

What are the 2 parts of the bilaminar disc?

Answer 3

**epiblasts **- columnar

hypoblasts - cuboidal

Question 4

What is the cavity above the bilaminar disc called?

What surrounds it? (2 things)

Answer 4

amnionic cavity

• amnion cells (uknown origin, either embryo- or trophoblast) on one side
• epiblasts on the other

Question 5

What is the cavity ‘below’ the bilaminar disc?

Answer 5

exocoelomic cavity

• AKA primary umbilical vesicle or yolk sac

Question 6

What cells forms all 3 germ layers?

Answer 6

epiblast cells

Question 7

What forms between the embryo and the cytotrophoblasts after bilaminar disc formation?

What membrane seperates the exocoelomic cavity from this?

Answer 7

extraembryonic mesoderm

• separate from yolk sac via Heuser membrane

Question 8

What structures form in the extraembryonic mesoderm?

And what happens to them?

Answer 8

extraembryonic coelomic cavities

• many small ones fuse into two big, fairly symmetrical ones on either side of the embryo

Question 9

During the formation of extraembryonic coelomic cavities and their fusion, what is happening to the cells within the embryo?

Answer 9

the hypoblast cells are dividing and turning inward to form a secondary yolk sac

• this separates from the primary yolk sac which is still surrounded by the Heuser membrane

Question 10

Once the extraembryonic coelomic cavities have fused and the secondary yolk sack has formed, how has the extraembryonic mesoderm changed?

Answer 10

it now has 2 layers

1. **splanchnopleura **- inner layer around embryo, forms abdominal wall later
2. somatopleura - outer layer just within cytotrophoblasts

Question 11

What are the cytotrophoblasts and somatopleura known as collectively?

Answer 11

Chorion

Question 12

What are the 2 steps of neuralation?

Answer 12

1. formation of the notochord (signal to ectoderm)
2. formation of the **neural tube **

Question 13

What are the 3 layers of the mesoderm?

Answer 13

1. **Paraxial **- forms somites, segments on back of embryo
2. **Intermediate - **gononephrotome
3. **Lateral - **pleura, peritoneum

Question 14

What are the 3 layers of the paraxial mesoderm?

Answer 14

1. dermatome - forms dermis
2. myotome - forms axial muscles
3. scleratome - forms bones of vertebral column

Question 15

What comes from the intermediate mesoderm?

Answer 15

gononephrotome

which gives rise to the urogenital system

Question 16

What develops from the mesoderm?

Answer 16

1. Dermis
2. Axial Muscles
3. Vertebral Bones
4. Urogenital System
5. Pleura
6. Peritoneum

(DAVUPP)

Question 17

What develops from the ectoderm and how?

Answer 17

thickenings of cranial ectoderm called placodes form structures

1. Lens of the eye (lens placode)
2. Receptors of the ear (otic placode)
3. Hypophysis
4. Epidermal epithelium

Question 18

What develops from the endoderm?

Answer 18

1. GI epithelium
2. Respiratory epithelium
3. Thyroid
4. Tonsils
5. Tympanic internal epithelium
6. Hepatocytes

(GRTTTH … growth)