Embryology week 15

Question 1

When does implantation of Blastocyst occur

Answer 1

• 6 to 10 days after fertilization

Question 2

As the blastocyst implants (at the start) what happens to the trophoblasts

Answer 2

Trophoblast differentiate into 2 layers :
- Cytotrophoblasts - Inner layer
- syncytiotrophoblasts- outer layer

Question 3

What happens in the second step ( Completion of implanation of blastocyst) starting with syncytiotrophoblasts

Answer 3

-Syncytiotrophoblast erodes endometrial tissue then the blastocyst become embedded in the endometrium
-Endometrial cells undergo apoptosis, aiding implantation.

Question 4

Explain what happens in the completion of Implantation of Blastocyst after the blastocyst is embedded in the endometrium

Answer 4

-Syncytiotrophoblast produces human chorionic gonadotropin (hCG).
-hCG maintains the corpus luteum, which secretes estrogen and progesterone to sustain pregnancy.
- By the end of the second week enough hCG is produced for a positive pregnancy test

Question 5

Name the 8 molecules that regulate implantation of the blastocyst

Answer 5

• Microvilli
  -Integrins
  -Cytokines
  -Prostaglandins
  -hCG
  -progesterone
  -growth factors
  -enzymes

Question 6

How is the Amniotic cavity formed

Answer 6

• A small space appears in the embryoblast, becoming the amniotic cavity
• Amnioblasts spereate from the epiblast to form the amnion,which encloses the amniotic cavoty

Question 7

How is the embryonic disc formed

Answer 7

• The embryoblast changes into a bilaminar embryonic disc with two layers:
• Epiblast
• Hypoblast

Question 8

-How is the Primary Umbilical vesicle formed
-What develops around the umbilical vessicle and amnion

Answer 8

• The hypoblast and exocoelomic membranes form the primary umbilical vesicle
• Extraembryonic mesoderm

Question 9

Where is lacunae formed

Answer 9

Syncytiotrophoblasts

Question 10

What is lacuneae

Answer 10

small spaces

Question 11

What does the lacunea fill with, and what does that form

Answer 11

• maternal blood and cellular debris
• forming embryotroph for nutrition

Question 12

How are decidual cells formed ?

Answer 12

• Endometrial connectove tissue cells accumulate glycogen and lipids, becoming decidual cells

Question 13

What is the function of decidual cells

Answer 13

• Provide nutrition and immune protection for the embryo

Question 14

How are lacunar networks formed

Answer 14

• lacunae fuse to form lacunae networks

Question 15

How is the Extraembryonic Coelom and secondary Umbilical vesicle formed

Answer 15

The Extraembryonic coelomic spaces merge to form the Extraembryonic coelom, surrounding the amnion and umbilical vesicle.
The primary umbilical vesicle shrinks, while a secondary umbilical vesicle forms

Question 16

Describe the umbilical vesicle

Answer 16

• Contains no yolk but plays a role in nutrient transfer
• where primordial germ cells origin

Question 17

Where does implantation sites occur

Answer 17

In the uterine endometrium in the superior part of the uterus

Question 18

Where is implantation more common the posterior or anterior wall

Answer 18

Posterior wall

Question 19

How can implantation be detected

Answer 19

Using ultrasonography
hCG radioimmunoassays can detect implantation

Question 20

Name the stages in forming the Chorionic Sac

Answer 20

• Formation of the Primary Chorionic Villi
• Splitting of the Extrembryonic Mesoderm
  -Formation of the Chorion and Chorionic Sac

Question 21

Explain the formation step of the primary Chorionic Villi:
- What it is induced by
- What the villi forms

Answer 21

• Growth is induced by the extrambryonic somatic mesoderm
• Forms columns with the syncytial coverings

Question 22

Explain what happens in the splitting of the Extraembryonic Mesoderm and each function (2nd step of chorionic sac development)

Answer 22

Splist into 2 :
-Extraembryonic somatic mesoderm: Lines the trophoblast and covers the amnion.
-Extraembryonic splanchnic mesoderm: Surrounds the umbilical vesicle

Question 23

Explain what happens in the formation of the chorion and chorionic sac:

Answer 23

-Chorion is formed by :
-Extraembryonic somatic mesoderm
- Two layers of trophoblasts

Question 24

What does the chorionic sac contain

Answer 24

• Embryo, amniotic sac, umbilical vesicle