Implantation, placentation and hormone changes in pregnancy

Question 1

What is the trophoblast?

Answer 1

• cells of blastocyst that invade endometrium + myometrium
• secrete beta-hCG

Question 2

What is the chorion?

Answer 2

that which becomes the placenta

Question 3

What is the aminion?

Answer 3

layer that becomes the amniotic sac

Question 4

When does the morula form and when does the blastocyst form?

Answer 4

• day 4 - morula
• day 5 - blastocyst

Question 5

What 4 events need to occur in order for implantation & placentation?

Answer 5

• differentiation of the trophoblast
• trophoblastic invasion of decidua + myometrium
• remodelling of maternal vasculature in utero-placental circulation
• development of vasculature within the trophoblast

Question 6

When is the window of implantation?

Answer 6

• day 5-6 of gestation
• really tight window, embryo has to be there at the right place + right time, in right part of uterus

Question 7

The trophoblast produces bHCG. What is the importance of this?

Answer 7

• “maternal recognition of pregnancy”
• maintenance of corpus luteum - progesterone production
• decidualisation under progesterone
• vital until placental steroidogenesis established

Question 8

bHCG is the basis of urinary pregnancy tests. When is it maximal?

Answer 8

• maximal by 9-11 weeks
• serum b-HCG (quantitative) useful for monitoring early pregnancy complications eg. ectopic pregnancy, miscarriage

Question 9

What are functions of the placenta?

Answer 9

• steroidogenesis - E₂, P, HPL, cortisol
• provision of maternal O_2, CHO, fats, AAs, vitamins, minerals, antibodies
• removal of CO₂, urea, NH₄, minerals
• barrier - eg. bacteria, viruses, drugs etc

Question 10

How is the placenta good at its job?

Answer 10

• huge maternal uterine blood supply - low pressure
• huge reserve in function
• huge surface area in contact w/ maternal blood
• highly adapted + efficient transfer system

Question 11

What will the connecting stalk turn into?

Answer 11

• umbilical cord

Question 12

Where is the commonest site of implantation?

Answer 12

• near fundus ~4 weeks
• receptive endometrium
• most successful pregnancies are here (around upper uterus)
• either posterior or anterior wall

Question 13

What and when are the 3 stages of stem villus development?

Answer 13

• primary stem villus (11-13 days)
• secondary stem villus (16 days)
• tertiary stem villus (21 days)

Question 14

What are cotyledons?

Answer 14

Big sections of placenta

Question 15

What are functions of the amniotic cavity?

Answer 15

• homeostasis - temp, fluid, ions
• vital for development of certain structure (limbs, lungs)
• protection - physical + barrier eg. ascending infection

foetus will breathe amniotic fluid very early on

Question 16

What are disorders of the placenta?

Answer 16

• miscarriage - 15% pregnancies
• pre-eclampsia - 3-4% pregnancies
• failure of IVF cycles - only 20% have successful implantation
• hydatidiform mole - too many paternal chromosomes, abn dvpt
• placental insufficiency - not enough nutrients for baby
• transfer of other substances - drugs, toxins, infections

Question 17

What is polyhydramnios?

Answer 17

• XS of amniotic fluid
• problem w/ normal control mechanism (baby breathes/swallow sit in) - could be structural problem eg. blockage, so fluid accumulates
• neuromuscular condition -> baby may not move or swallow
• if a very big placenta producing lots of fluid
• or baby with high glucose levels (mum w diabetes), so baby urinates a lot -> inc fluid

Question 18

What is oligohydamnios?

Answer 18

• lack of amniotic fluid
• severe placental insufficiency?

Question 19

What is premature rupture of membranes?

Answer 19

• normal from 37 weeks onwards
• but if it happens 24-25 weeks -> can cause major problems

Question 20

Placental steroidogenesis takes place from around 7-8 weeks. One steroid produced is progesterone - what is the importance of this?

Answer 20

• corpus luteum still making P but placenta will take over soon
• decidualisation (CL)
• smooth muscle relaxation - uterine quiescence
• mineralocorticoid effect - cardiovascular changes
• breast development

Question 21

What does oestrogen (in pregnancy) rely on? What is the purpose of it?

Answer 21

• E3 > E2 > E1
• rely on androgens from fetus + maternal adrenals
• contribute to:
  
  • development of uterine hypertrophy
  • metabolic changes (insulin resistance)
  • cardiovascular changes
  • breast development

Question 22

Hormone changes in pregnancy: CRH

Answer 22

• increase from T2 onwards
• possibly involved in labour initiation (“placental biological clock”)

Question 23

Hormonal changes in pregnancy: Cortisol

Answer 23

• increase from T2 onwards
• for metabolic changes (insulin resistance)
• for fetal lung maturity

Question 24

Hormonal changes in pregnancy: Human Placental Lactogen (HPL)

Answer 24

• similar to GH
• metabolic changes - insulin resistance
• possibly some role in lactation

Question 25

Hormonal changes in pregnancy: Prolactin

Answer 25

* increases throughout pregnancy * breast development for lactation