TOB CL 5 Germinal Layers

Question 1

2nd week development of embryo

What happens in day 8 ? (5)

Answer 1

1. Blastocyst embedded partially in endometrium
2. Trophoblast:
   - Cytotrophoblast - mononucleated, distinct cell boundaries, mitosis
   - Syncytiotrophoblast - multinucleated, no distinct cell boundaries, no mitosis
3. Embryoblast: bilaminar
   - Epiblast - face amniotic cavity
   - Hypoblast - face blastocyst cavity
4. amnioblast derived from epiblast
5. Endometrium wall is oedematous, highly vascular, glandular secretes glycogen & mucous to endometrium stroma cavity

Question 2

2nd week development of embryo

What happens in day 9 ? (3)

Answer 2

1. Blastocyst embedded into endometrium wall more deeper
   - closed by fibrin coagulum
2. Vacuoles in syncytium combine tgt to form trophoblast lacunae
3. Extraembryonic membrane (Heuser’s membrane) is formed
   - Blastocyst cavity changed name > Exocoelomic cavity ( primitive yolk sac )

Question 3

2nd week development of embryo

What happens in day 11&12 ? (4)

Answer 3

1. Blastocyst embedded into endometrium wall completely
2. Maternal Sinusoids
   - congested & dilated capillaries
3. Maternal blood into lacunae > uteroplacental circulation is established
4. Extraembryonic mesoderm
   - extraembryonic splanchnic ( facing cavity )
   - extraembryonic somatic ( facing trophoblast )
   - extraembryonic coelom ( middle )

Question 4

2nd week development of embryo

What happens in day 13 ? (3)

Answer 4

1. primary villi
   - cytotrophoblast penetrate into syncytiotrophoblast
2. Formation of chorionic cavity
   - Extraembryonic coelom expands into single large cavity > Chorionic cavity
   - Extraembryonic somatic > chorionic plate
   - Extraembryonic somatic + splanchnic connected to connecting stalk
3. Formation of umbilical cord
   - connecting stalk marks the caudal end of embryo
   - blood vessels developed
   - become umbilical cord

Question 5

3rd week development of embryo

What happens in Gastrulation ?

Answer 5

1. Formation of primitive streak ( groove, node, pits )
   - p. groove - groove in p. streak
   - p. nodes - slightly elevated area
   - p. pits - depression in p. nodes
2. Invagination ( trilaminar )
   - Epithelial cells to p. streak
   - cells forms flask-shaped and detached epiblast
   - displaced hypoblast > endoderm
   - between epiblast and hypoblast > mesoderm
   - remaining epiblast > ectoderm

Question 6

3rd week development of embryo

What happens in Notochord ?

Answer 6

Prenotochord migrates to p. node > forms solid chord > notochord> axial skeleton

Question 7

Which area do not have mesoderm, held tightly of endoderm and ectoderm ?

Answer 7

buccopharyngeal membrane & coacal membrane

Question 8

3rd week development of embryo

What is in the fact of germ layer ?

Answer 8

Ectoderm
- skin (epidermis )
- sensory epithelium
- central & peripheral nervous system

Mesoderm
- paraxial, intermediate, lateral ( muscle, joint, cartilage etc. )

Endoderm
- epithelial lining of internal organs ( GI tract, respiratory tract , urinary bladder )

Question 9

Placenta development : Trophoblast
primary villi?
secondary villi ?
tertiary villi ?
outer cytotrophoblast ?
anchoring villi ?
branching villi ?

Answer 9

1. cytotrophoblast into syncytiotrophoblast
2. mesoderm penetrate into the core
3. blood vessel differentiate, cytotrophoblast x continuous, connects chronic plate to connecting stalk
4. cytotrophoblast reaches the maternal endometrium
5. chronic plate > outer cytotrophoblast
6. stem villi > intervillous space

Question 10

Maternal endometrium: decidual reaction (3)

Answer 10

1. Endometrium stroma cells - polyhedral & oedematous
2. loaded with glycogen & lipid - decidual cells
3. provide immunologically privileged site to the embryo