REPRO: Implantation, Placentation and Hormone Changes in Pregnancy

Question 1

What are trophoblasts?

Answer 1

They are cells of the blastocyte that invade the endometrium and myometrium (day 5-6).
They secrete βhCG (human chorionic gonadotrophin).

Question 2

What are the chorion and the amnion?

Answer 2

The chorion is that which becomes the placenta.

The amnion is the layer that becomes the amniotic sac.

Question 3

What sequentially happens during the early stages of pregnancy?

Answer 3

• there is differentiation of the trophoblast
• trophoblastic invasion occurs, of the decidua and the myometrium
• remodelling of the maternal vasculature in the uteroplacental circulation
• development of the vasculature within the trophoblast

Question 4

How long is the window of implantation?

Answer 4

It is between 24-36 hours, between Day 5-6.

Question 5

Describe βhCG.

Answer 5

It is the hormone known as the ‘maternal recognition of pregnancy’. It’s maximal at 9-11 weeks, and is the basis of urinary pregnancy tests (testing for the β subunit).

Serum βhCG (quantitative) is useful for monitoring early pregnancy complications, eg. ectopic pregnancies, miscarriages, etc.

It helps with the maintenance of the corpus luteum, thus maintaining progesterone production.

Question 6

What is decidualisation?

Answer 6

Decidualisation is a process that results in significant changes to cells of the endometrium in preparation for, and during, pregnancy.

In humans, it happens before fertilisation even occurs.
Decidualisation happens under progesterone, so it is vital that it keeps getting released until placental steroidogenesis is established.

Question 7

What are some functions of the placenta?

Answer 7

1. Steroidogenesis - oestrogens, progesterone, HPL, cortisol
2. Provision of maternal O2, CHO, fats, amino acids, vitamins, minerals, antibodies, etc.
3. Removal of CO2, urea, NH4, minerals
4. Acts as a barrier against, for example, bacteria, viruses, drugs, etc.

Question 8

How is the placenta adapted to be good at its job?

Answer 8

• a huge maternal uterine blood supply, at low pressure
• a huge reserve of function
• a huge surface area in contact with maternal blood
• highly adapted and efficient transfer system

Question 9

What is the function of the amniotic cavity?

Answer 9

• homeostasis: temperature, fluid, ions
• vital for the development of certain structures: eg. limbs, lungs
• protection: physical, and act as a barrier, eg. ascending infection

Question 10

List some disorders of the placenta.

Answer 10

• miscarriages (account for 15-40% of pregnancies, depending on what is considered)
• pre-eclampsia - 3-4% of pregnancies, it’s where the placenta essentially gets sick
• hydatidiform mole (when a cluster of cells fill the uterus, causing it to grow rapidly; over-placentation)
• placental insufficiency
• transfer of other substances (eg. drugs, toxins, infections)

Question 11

List some disorders of the amnion.

Answer 11

• POLYHYDRAMNIOS: too much fluid
• OLIGOHYDRAMNIOS: too little fluids
• PREMATURE RUPTURE OF MEMBRANE: total lack of fluid

Question 12

What are the different kinds of hormones that come into play during the hormonal changes of pregnancy?

Answer 12

• placental steroids
• maternal steroids
• foetal steroids
• placental peptide hormones

Question 13

Describe the actions of progesterone, with regards to hormonal changes in pregnancy.

Answer 13

Placental steroidogenesis takes place at about 7-8 weeks. It produces progesterone.

It is thought that progesterone is responsible for decidualisation (with the corpus luteum). It is also involved in smooth muscle relaxation (uterine quiescence) and breast development. It also has a mineralocorticoid effect (cardiovascular changes).

Question 14

Describe the actions of oestrogen, with regards to hormonal changes in pregnancy.

Answer 14

Oestrogens (E1, E2, E3) rely on androgns coming from the foetus and maternal glands

They are responsible for:

• the development of uterine hypertrophy
• metabolic changes (insulin resistance)
• cardiovascular changes
• breast development

Question 15

Describe cortisol and placental CRH, with regards to hormonal changes in pregnancy.

Answer 15

With placental CRH and cortisol, both of their levels increase from T2 onwards.

Cortisol is responsible for:

• metabolic changes (insulin resistance)
• foetal lung maturity

Placental CRH is responsible for:
- possibly involved in labour initiation (‘placental biological clock’)

Question 16

Describe HPL, with regards to hormonal changes in pregnancy.

Answer 16

HPL (human placental lactogen) is similar to GH.
It is responsible for:
- metabolic changes (insulin resistance)
- possible some role in lactation

Question 17

Describe prolactin, with regards to hormonal changes in pregnancy.

Answer 17

Prolactin increases during pregnancy.

It is responsible for breast development, for lactation.