Implantation and Maternal Recognition

Question 1

What are the key stages in the establishment of pregnancy?

Answer 1

Pre-implantation development
Implantation
Signals its presence
Maternal recognition of pregnancy

Question 2

How long do blastocysts stay in the free living phase?

Answer 2

Depends on the animal (in humans its short 4-6 days).

Question 3

How is the blastocyst and embryo maintained - what are the two types of nutrition?

Answer 3

Histiotrophic nutrition (material secreted into uterine lumen by endometrium and transfers to trophectoderm). If this becomes inadequate…

Haemotrophic nutrition occurs (needs adjacent maternal and fetal curculations in the placenta for diffusion, endocytosis fluid uptake, carrier based mechanisms e.g active transport).

Question 4

Is the timing of implantation important?

Answer 4

Yes

Question 5

What are the 3 phases of the implantation window?

Answer 5

Pre-receptive - mucin coat resists implantation

Receptive - thining of mucin, microvilli shorten and low surface change, integrin and extracellular matrix interactions - inplantation can happen

Refractory - resistant to implantation

Question 6

Is degree of twinning reliant on the timing of the split?

Answer 6

Yes

Question 7

What are the implantation steps?

Answer 7

1) Hatching
2) Apposition (adhesion molecules and signals help it bind)
3) Adhesion (adhesion molecules and signals help it bind)
4) Invasion (this is the placenta - can cause miscarriage if doesnt happen or if it goes to far can be dangerous)

Question 8

What is attachment?

Answer 8

Tethering by carbohydrates - lectin binding

Heparin binding EGF-like growth factor with trophoblasts expressing EGF and heparin suphate proteoglycans - stimulates invasion.

Integrins

Question 9

Leukemia inhibitory factor (LIF) - what does this do?

Answer 9

If knocked out the mice is still fertile but there is no implantation. If you were then to put this mouses blastocyst into a wildtype then pups would be born.

This is critical for mice pregnancies but not human

Question 10

How does invasion happen?

Answer 10

After blastocysts has burrowed into endometrium decidualisation response occurs - cells are secretory

Angiogenesis happens

Tissue is broken down and remodelled (matrix metalloproteinases)

There is cell-cell interactions which are critical to ensure appropriate amount of invasion for placentation

Question 11

What cells invade?

Answer 11

Trophoblasts which will then form the placenta

Question 12

What are the three maternal recognition of pregnancy system?

(these signal to mother to maintain progesterone and function of the corpus luteum (CL))

Answer 12

Luteotrophic

Anti-luteolytic

Coitus initiates maintenance of CL

Question 13

How does the luteotrophic mechanism help with maternal recognition of pregnancy? (what hormones are important here)

Answer 13

Chorionic gonadotrophin (hCG) is secreted by trophoblasts which have high homology with LH and FSH.

It binds to LH receptor on large luteal cells of the CL to maintain and stimulate progesterone secretion.

Question 14

How does the anti-luteolytic mechanism work?

Answer 14

Interferon is secreted by trophoblasts and inhibits endometrial PGF alpha secretion (would normally break down the CL and lose progesterone)

Normal in sheep and cows

Question 15

How does the coitus initiation maintain the CL?

Answer 15

This happens in mice and rats and coitus stimulates a nocturnal surge of prolactin which maintains the CL.

Pseudopregnancy can be initiated using infertile males

Question 16

What is the luteul placental shift?

Answer 16

The placenta at around 6 weeks will secrete enough progesterone to maintain the pregnancy without the CL.

Rodents still need the CL

Question 17

What mechanism do woman and mares use?

Answer 17

Luteotrophic

Question 18

What mechanism do cow, eye and sow use?

Answer 18

Anti-luteolytic

Question 19

Is the CL essential throughout pregnancy for women?

Answer 19

No (read question - if crucial at start but not end).