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 ICM and the trophoblasts?

Answer 2

Embryoblast or inner cell mass (ICM) - gives rise to the foetus

The cells which surround the inner cell mass are called the trophoblast - this gives rise to the placenta.

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

• Provision of maternal O2, CHO, fats, amino acids, vitamins, minerals,
  antibodies.
• Site of metabolism e.g. synthesis of glycogen from maternal substrates
• Barrier e.g. against bacteria, viruses, drugs etc - not 100% fail safe as sometimes makes its way through (barrier formed by the cells of the villi)
• Removal of foetal waste products e.g. CO2, urea, NH4, minerals.
• It is a site of endocrine secretion e.g. hCG, oestrogens, progesterone, HPL, cortisol.

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

List some disorders of the placenta.

Answer 9

• Pre-Eclampsia
• Placental Abruption
• Placenta Previa

Question 10

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

Answer 10

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

Question 11

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

Answer 11

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 12

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

Answer 12

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 13

Describe HPL, with regards to hormonal changes in pregnancy.

Answer 13

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

Question 14

Describe prolactin, with regards to hormonal changes in pregnancy.

Answer 14

Prolactin increases during pregnancy.

It is responsible for breast development, for lactation.