Implantation And Formation Of Germ Layers

Question 1

Decidual reaction

Answer 1

Oestrogen and progesterone signalling leads to decidualisation throughout uterus;
Bone morphogenetic protein (BMP2) non-active precursor protein is cleaved by pro protein convertase (PC6) to produce active form;

Deletion or knockdown of BMP2 or PC6 inhibits decidualisation - implantation failure and female infertility;

Question 2

Cervical mucus plug

Answer 2

Oestrogen stimulate production of mucus from glands at cervix;
A plug which acts in a mechanical and antibacterial manner;

Question 3

Twins

Answer 3

Division of zygote into 2 embryos;
99% within 8 days of fert;
Normally 2 separate curious and amnions

Question 4

Dichorionic-diamniotic

Answer 4

DiDi;
Lowest mortality rate - 9% (more than singletons);
Split by 3rd day;
Almost all cases of monozygotic twins (identical)

Question 5

Monochorionic

Answer 5

Same placenta;
Risk of twin to twin transfusion syndrome;
60-70% of mz twins;

Question 6

Monoamniotic

Answer 6

Same amniotic sac;
Umbilical cord may tangle around babies - increased miscarriage or suffer from cerebral palsy due to brain due to lack of oxygen;
Split on 9th day of fert;

Question 7

Conjoined twins

Answer 7

Division of zygote occurs later than 12 days post fert;
Complications due to shared organs;
Highest mortality rate;

Question 8

Hydatidiform mole

Answer 8

Only trophoblastt layers proliferate - no embryo develops;
Trophoblast secretes HCG as in normal pregnancy;
Appears maternally and by preg test to be normal;
Diagnosis by ultrasound - absence of embryo;
Forms: partial, complete, persistent gestational trophoblastic tumour;
Arise from haploid sperm fertilizing an egg without a female pronucleus;
1% risk of second molar pregnancy;

Question 9

Blastocyst implantation

Answer 9

6 days post fert;
Adheres to endometrium;
Closer to fundus than cervix;
Posterior wall of uterus;

Question 10

Blastocyst gives rise to

Answer 10

Inner cell mass - primitive endoderm and primitive ectoderm;

Trophoblast - invasive, digestive, ingestive;

Question 11

When does implantation begin?

When is the blastocyst completely implanted?

Answer 11

6 days post fert;

10 days post fert;

Question 12

Abnormal implantation

Answer 12

Ectopic pregnancy - implantation in uterine tube;
If not spontaneously aborted, embryo removed surgically;
Tends to occur if uterine epithelium is damaged (scarring, pelvic inflammatory disease), if zona pellucida lost too early, allows premature tube implantation;

Embryo may develop through early stages, can erode through the uterine horn and reattach within peritoneal cavity (external surface of uterus, ovary, bowel, gastrointestinal tract)

Question 13

Third week

Answer 13

3 germ layers;

Notocord, neural tube, primitive streak;