Implantation, Placentation, Embryonic Development

Question 1

Describe the 4 main steps in ovarian embryology

• primordial germ cells
• mitosis only
• mitosis, meiosis
• what process is dominant here

Answer 1

Primordial germ cells migrate to genital ridge => sex differentiation

Mitosis only until wk8

Mitosis, meiosis in wk8-28

Wk 20 onwards, atresia dominates

Question 2

Blastocyst implantation

• apposition
• attachment
• penetration or not

Answer 2

Cytokine communication => loose endometrial connection

Trophoblast microvilli and endometrium interact

Penetration requires PG
-decidual cells on endometrium trigger stress response => prevents abnormal embryos

Question 3

What are the 2 cells that make up the trophoblast

Answer 3

Cytotrophoblast
-mononuclear inner cells

Syncytiotrophoblasts
-pentrate endometrium

Question 4

Describe how cytotrophoblasts are involved in the formation of chorionic villi

Answer 4

Primary
-cytotrophoblastic core

Secondary
-mesodermal core

Tertiary

• villous capillaries, connect embryonic heart to chorion
• but nutrients initially provided histiotrophically

Question 5

Describe how the syncytiotrophoblasts are involved in the formation of the connection between the endometrium and the placenta

How does the syncytiotrophoblasts help maintain the pregnancy at this early stage

Answer 5

Lacunae form
Penetrate and erode maternal sinusoids (D8)

Produce hCG, maintains CL => maintains P

Question 6

Describe how the maternal circulation is formed

Answer 6

Differentiation of endometrium => decidua
-results in changes to prepare for pregnancy

NK, spiral artery changes

• NK cells trigger spiral artery opening at wk12
• allows for haematogenous transport

Placenta attains final form at month 4

Question 7

What issues could arise when the spiral arteries fail to form properly

• inadequate
• too early

Answer 7

Inadequate

• FGR
• PET

Too early

• fail to implant
• miscarriage
• congenital malformations

Question 8

Describe the relative susceptibility to teratogens at

• 0-2wks
• 3-8wks (embryonic)
• 9+ (fetal)

Answer 8

0-2

• low sensitivity
• high lethality

3-8
-highest sensitivity as organs mainly develop during this phase

9+
-low sensitivity as most organs are fully formed

Question 9

Describe how the no of chorions and amnions change with the cleavage of a single egg

Answer 9

Cleavage before implantation at morula stage (D1-4)
-DC, DA

Cleavage before implantation at blastocyst (D4-8)
-MC, DA

Cleavage after implantation (D8+)
-MC, MA