Implantation, Placentas and Hormonal Changes in Pregnancy

Question 1

what is the trophoblast

Answer 1

Cells of the blastocyst that invade the endometrium and myometrium and will become the placenta.
The trophoblast secretes beta-hCG initially

Question 2

what is the chorion

Answer 2

the outermost membrane surrounding an embryo.

goes on to become placenta

Question 3

what is the amnion

Answer 3

the amniotic sac in which the baby sits

Question 4

what happens to the oocyte once it becomes fertilised

Answer 4

1. egg fertilised in ampullary region of uterine tube
2. zygote wafted down uterine tube and starts to divide
3. Day 4 = 32 cells. becomes morula
4. morula is compacted. becomes blastocyst.
5. blastocyst enters uterus at day 5/6

Question 5

what is the morula

Answer 5

early stage embryo consisting of cells (called blastomeres) in a solid ball contained within the zona pellucida.
only 32 cells

Question 6

what is the structure of the blastocyst

Answer 6

• has an inner cell mass stuck to its inner wall
• surrounded on inside by blastocoele
• trophoblast lines structure
• has small zona pellucida around it.

Question 7

what happens if embryo is implanted too early

Answer 7

unable to implant

Question 8

what happens if embryo is implanted too late

Answer 8

if delayed in travelling down uterine tube, can implant in uterine wall = ectopic pregnancy

Question 9

what is the luteal phase

Answer 9

occurs after ovulation and before your period starts

Question 10

at day 20 (period start) of menstrual cycle, what is the structure of the uterus

Answer 10

endometrium is thick, approaching thickest levels

• very vascular. glands well differentiated.
• endometrium ready to receive the blastocyst.
• progesterone levels increasing

Question 11

what are the 4 main stages of implantation and placentation

Answer 11

1. Differentiation of the trophoblast
2. Trophoblastic invasion of decidua and myometrium
3. Remodelling of the maternal vasculature in the uterus
4. Development of vasculature within the trophoblast

Question 12

what is meant by placentation

Answer 12

formation of placenta in a woman’s uterus

Question 13

when, roughly, is the window of implantation

Answer 13

day 5-6

window is about 24-36 hours

Question 14

which structure produced b-hCG

Answer 14

trophoblast

Question 15

what is the role of b-hCG in pregnancy

Answer 15

• is maternal recognition mechanism of pregnancy
• binds to and maintains corpus luteum
• by maintaining CL, progesterone and oestrogen production continues
• former prevents menstruation

Question 16

what is the corpus luteum

Answer 16

corpus luteum is a temporary endocrine structure involved in ovulation and early pregnancy

Question 17

what is meant by decidualisation

Answer 17

a process that results in significant changes to cells of the endometrium in preparation for, and during, pregnancy.

Question 18

what hormone allows for decidualisation

Answer 18

progesterone

Question 19

what hormone is the basis of pregnancy tests

Answer 19

b-HCG

Question 20

for how long is b-hCG needed to maintain the corpus luteum

Answer 20

7-8 weeks.

However hCG doesn’t decrease to zero at all.

Question 21

at what point are b-hCH levels at their peak

Answer 21

usually maximal b-hCG levels by 9-11 weeks

and then start to drop again

Question 22

why may clinicians need a qualitative value of b-hCH and how do they measure it

Answer 22

measure serum b-hCG
useful in monitoring:
early pregnancy complications such as ectopic pregnancy and miscarriage

Question 23

what takes over the role of corpus luteum at 8 weeks

Answer 23

placenta

Question 24

what is b-hCG decreasing in early pregnancy indicative of

Answer 24

miscarriage

Question 25

what is b-hCG increasing very slowly in pregnancy indicative of

Answer 25

ectopic pregnancy

Question 26

when are b-hCG levels clinically useful

Answer 26

hCG is useful clinically immediately for diagnosis of pregnancy, but then only for the next 4-8 weeks to monitor its increase.

Question 27

roles of placenta

Answer 27

• steroidogenesis
• exchange
• barrier

Question 28

role of placenta in steroidogenesis

Answer 28

produce and secrete steroids
such as:
oestrogens, progesterone, hPL, cortisol

Question 29

role of placenta in exchange

Answer 29

act as exchange organ to allow provision of O2, carbohydrates, fats, amino acids, vitamins, minerals and antibodies.
also allows removal of waste such as CO2, urea, ammonia and minerals

Question 30

role of the placenta in being a barrier

Answer 30

even if the mother has a bacterial infection, viral infection or taking certain drugs, placenta does not allow these to reach foetus

Question 31

how is the placenta specialised for its function

Answer 31

huge maternal uterine blood supply (high volume low pressure)

• reserve function (if part gets damaged it can continue to function without harmful effects)
• large SA in contact with maternal blood so well perfused

Question 32

at what stage of pregnancy does implantation occur

Answer 32

day 7

Question 33

how does trophoblast implant

Answer 33

day 7- blastocyst stats to implant
trophoblast invades endometrium and differentiates into syncitiotrophoblast &cytotrophoblast which invade deeper into uterine wall.
- formation of the bilaminar germ disc
- amniotic cavity is bound by the epiblast
——————————————————————————————————————————————————————————to be continued

Question 34

what is the syncitiotrophoblast

Answer 34

a mesh of cells, it contains no cell membranes

formed from trophoblast to invade uterine wall to establish nutrient circulation between the embryo & the mother

Question 35

what is the cytotrophoblast

Answer 35

the inner layer of the trophoblast

Question 36

what does the bilaminar germ disk comprise of

Answer 36

composed of an epiblast and hypoblast

Question 37

what is the epiblast

Answer 37

gives rise to the three primary germ layers (ectoderm, definitive endoderm, and mesoderm)
and to the extraembryonic mesoderm of the visceral yolk sac, the allantois, and the amnion