Implantation

Question 1

Describe the effect oestrogen and progesterone have on the endometrium

Answer 1

They are both hydrophobic and so can pass through the cell membrane. Their receptors are transcription factors.

Oestrogen thickens the endometrium.
Progesterone changes the proteins on the endometrial surface to be receptive to embryos

Question 2

State the layers of the uterus

Answer 2

Endometrium
- functionalis
-basalis

Myometrium

Perimetrium

Question 3

State the time period for the window of receptivity?

Answer 3

6-10 days post LH surge

Question 4

What thickness does the endometrium require to be ready for implantation

Answer 4

12-14mm

Question 5

What are steroid response elements?

Answer 5

Specific DNA sequences found within the promoter regions of genes.

They are binding sites for steroid hormone receptor complexes.

Question 6

What 2 factors are important for implantation

Answer 6

Endometrium receptivity
Embryo with ability to implant being released at the correct time

Question 7

Name the steps of implantation

Answer 7

• Hatching - which occurs 1-3 days after entering the uterus
• apposition - which occurs 2-4 days after entering the uterus
  -Attachment
  -Invasion

Question 8

Name the 4 models of Oestrogen receptor interaction with DNA

Answer 8

-Classic model
-Tethered model
-Non-genomic model
-Ligand independent model

Question 9

Describe the classic model of oestrogen receptor interaction with DNA

Answer 9

O receptor interacts directly with DNA once O has attached

Question 10

Describe the tethered model of oestrogen receptor interaction with DNA

Answer 10

DNA binding receptor binds to other scaffolding proteins rather than binding to DNA directly

Question 11

Describe the non-genomic model of oestrogen receptor interaction with DNA

Answer 11

Doesn’t interact with DNA at all. Will interact with other signalling pathways to change gene expression

Question 12

Describe the ligand independent model of oestrogen receptor interaction with DNA

Answer 12

The o receptor binds to DNA based on other factors, not activated by o binding

Question 13

What factors/ receptors does oestrogen play an important role in upregulating?

Answer 13

• Progesterone receptors (endometrium is not receptive to progesterone without oestrogen)
  -VEGF
  -IGF-1
  -HB-EGF
  -L-selectin

Question 14

Describe the two mechanisms of the progesterone receptor action once progesterone has bound

Answer 14

-genomic
-non-genomic - binding to progesterone receptor changes other signalling pathways

Both result in change in gene expression

Question 15

Name three implantation failure causes

Answer 15

• Embyronic factors
  -Endocrine factors
  -Male gamete factors

Question 16

Describe hatching

Answer 16

As the blastocyst expands it stretches and thins the ZP causing hatching.

Both the embyro and the endometrium produce proteases to help break down the ZP.

Under the influence of O and P, both the endometrium and embyro produce factors that interact with each other - such as VEGF, LIF, IGF-1, HB-EGF

Question 17

Describe apposition

Answer 17

Non-permanent interaction with rolling adhesion.

L-selectin on the embyro binds transiently to L-selectin oligosacarride receptors on the endometrium. This way the embryo crawls along the endometrial wall until it reaches the correct site for implantation

Question 18

Describe attachment

Answer 18

The embryo attaches firmly at a specific implantation site.
Mucin proteins line the endometrium and at the implantation site their is less so that the embryo can bind to receptors.

There are pinopodes which maintain the fluid balance within the endometrium by regulating ion transfer. This reduces the amount of fluid in the endometrium making it easier for the embyro to bind.

The embyro binds securely with Integrins. Embryo has complementary receptors.

Question 19

Describe IL1B function

Answer 19

IL1B is a factor produced by the embryo to increase the number of integrin receptors present on the endometrium surface.

It also has autocrine signalling factors that influence the embryo’s ability to produce VEGF.

Question 20

What does Glycodelin A do?

Answer 20

It initibits natural killer activity
Dampens down the immune response
Changes the architecture of immune cells

Question 21

Describe the role of the MMP

Answer 21

Matrix metalloproteiases are a family of enzymes:
- the gelatinases
- MMP 2
- MMP 9

They break down collagen IV and therefore help the embyro to invade into the endometrium.