Early embryogenesis and foetal growth

Question 1

What is the zona pellucida, and what happens if it fails?

Answer 1

The reaction produced by an oocyte when a single sperm penetrates, thus preventing further sperm from penetrating the cell
Failure can lead to polyspermy
Dispermy causes chromosome complement of 69 - leads to partial hydatidiform mole

Question 2

Tubal transport of fertilised egg

Answer 2

Fertilisation occurs in fimbrial end of ovarian tubes
Muscular contraction of the tube + cilia cause movement of egg to uterus
Adhesion molecules also involved

Premature implantation in the tube can occur by abnormal interaction with adhesion molecules

Question 3

What is decidualisation of the uterus

Answer 3

Response of the endometrial wall to progesterone to prepare the endometrium for implantation

Question 4

What is the decidua?

Answer 4

The thick layer of modified mucous membrane making up the endometrium during pregnancy, that is shed with afterbirth (down to deepest layer)

Question 5

Immunotolerance in implantation of a fertilised oocyte

Answer 5

TH-1 response - attacks foreign material at first phase of pregnancy - angiogenesis into decidua, NK cells remodel tissues
TH-2 response suppresses function of NK cells
Progesterone responsible for switch from defence to acceptance processes

Question 6

Normal process of placentation

Answer 6

Trophoblast invasion:
Trimester 1: trophoblasts destroy and replace endothelial and smooth muscle layers of maternal spiral arteries, converting to large, wide bore, low resistance vessels
Trimester 2: trophoblast progresses to invade through outer third of myometrial component of vessels
Trimester 3: no more development of placentation