8.1: Reproductive system (embryo, lecture) 1

Question 1

in very early embryonic development, what takes precedence?

Answer 1

establishment of the placenta

Question 2

why is establishment of the placenta so important?

Answer 2

ensures support for the pregnancy

Question 3

what happens in week two? (the week of twos)?

Answer 3

differentiation:

2 distinct cellular layers emerge

Question 4

what are the outer cell mass of week 2? (2 of 2)

Answer 4

outer cell mass:
syncytiotrophoblast
cytotrophoblast

Question 5

what do the inner cell mass form in week 2?

Answer 5

bilaminar disk

Question 6

what are components of the bilaminar disk?

Answer 6

inner cell mass:
epiblast
hypoblast

Question 7

what are the cavities early on (1 week post fertilisation)?

Answer 7

at first blastocyst cavity (blastocoele) - within trophoblast
then amniotic cavity appears within the epiblast cellular layer

Question 8

what happens at around day 6 of fertilisation?

Answer 8

syncytiotrophoblast invade the maternal uterine epithelium layer
(breaching of endometrium)

Question 9

what happens post implantation?

Answer 9

the syncytiotrophoblast makes contact with glands of endometrium and communicate
e.g. lacuna and uterine gland

there is rich vascularisation within endometrium - establish new circulation and units of exchange

Question 10

what has happened by the end of week 2?

Answer 10

conceptus has implanted

embryo and its cavities (amniotic cavity and yolk sac) suspended via CONNECTING STALK within chorionic cavity

Question 11

what does the connecting stalk suspending the embryo and its cavities become?

Answer 11

modified to become umbilical cord

communicate between embryo and internal maternal circulation

Question 12

what is the amniotic cavity arising from epiblast of embryoblast also known as?

Answer 12

amion

where the embryo grows

Question 13

what are the 3 major cavities during embryonic development?

Answer 13

yolk sac
amniotic cavity
chorionic cavity

Question 14

as the embryo develops what happens to the yolk sac, amniotic sac and chorionic sac?

Answer 14

yolk sac disappears

amniotic sac enlarges within the chorionic sac

Question 15

how can you describe implantation?

Answer 15

interstitial (occupies interstitium space) as uterine epithelium is breached

Question 16

where does the conceptus implant?

Answer 16

within the stroma

Question 17

what happens to the placental membrane as the foetus develops?

Answer 17

becomes progressively thinner as NEEDS of foetus increases

Question 18

how is the human placenta?

Answer 18

haemomonochorial

Question 19

what is haemomonochorial (human placenta)?

Answer 19

1 layer of trophoblast ultimately separates maternal blood from foetal capillary wall
(maternal blood bathing: trophoblast + foetal endothelium)

Question 20

what are the 3 aims of implantation?

Answer 20

1. establish basic unit of EXCHANGE
2. ANCHOR the placenta
3. establish MATERNAL blood flow within placenta

Question 21

how is basic unit of EXCHANGE between mother and foetus achieved?

Answer 21

via primary, secondary and tertiary villi

Question 22

what are primary villi in basic unit of exchange from implantation?

Answer 22

early finger-like projections of TROPHOBLAST (outer cell mass)
(cytotrophoblast surrounded by syncytiotrophoblast)

Question 23

what are secondary villi in basic unit of exchange from implantation?

Answer 23

INVASION of MESENCHYME into cytotrophoblast core

now mesoderm core within cytotrophoblast, surrounded by syncytiotrophoblast

Question 24

what are tertiary villi in basic unit of exchange from implantation?

Answer 24

invasion of mesenchyme core by foetal vessels

now vessels within mesenchyme < cytotrophoblast < syncytiotrophoblast

Question 25

how does implantation anchor the placenta?

Answer 25

establishment of the outermost cytotrophoblast shell

Question 26

what is the cytotrophoblast shell (anchor placenta)?

Answer 26

the external layer of cytotrophoblasts from the foetus that is found on the maternal surface of the placenta

Question 27

what are the 2 major excessive implantation defects?

Answer 27

ectopic pregnancy | placenta praevia

Question 28

what is ectopic pregnancy?

Answer 28

implantation at site other than uterine body (most commonly fallopian tube) although can be peritoneal or ovarian can v quickly become life-threatening emergency

Question 29

what is placenta praevia?

Answer 29

implantation in lower (1/3) uterine segment can cause haemorrhage in pregnancy requires C-section

Question 30

why does placenta praevia require C-section?

Answer 30

placenta grows across internal os internal os completely occluded by placenta birth canal cannot function, therefore requires c-section

Question 31

histology of the endometrium: how does endometrium prepare for implantation? (cells and arterial blood supply)

Answer 31

'pre-decidual cells' elaboration of spiral arterial blood supply (endometrium prepared for implantation)

Question 32

what is decidualisation?

Answer 32

the decidual reaction provides the balancing force for the invasive force of the trophoblast (syncytiotrophoblast invade endometrium - uterine lining) a response of maternal cells

Question 33

where are desidual cells present?

Answer 33

only in maternal endometrium therefore can control invasive process of implantation within endometrium by preventing syncytiotrophoblast implanting further than endometrium, into myometrium then pelvis (surrounding blood vessels etc.)

Question 34

describe the process of desidualisation within ectopic pregnancy

Answer 34

there aren't decidual cells within the fallopian tube (ONLY in endometrium), therefore in ectopic pregnancy, there is no control over the invasive process, leading to trophoblast continue to invade into vessel within the pelvis, causing risk of haemorrhage within ectopic pregnancy

Question 35

why is remodelling of the spiral arteries necessary?

Answer 35

create low resistance vascular bed maintains high flow required to meet foetal demand (particularly late in gestation) HIGH FLOW, LOW RESISTANCE (relationship between spiral arteries of endometrium with trophoblast of embryo)

Question 36

histologically, where are decidual cells found?

Answer 36

surrounds myometrium like a cuff

Question 37

what are the 2 major incomplete invasion defects?

Answer 37

placenta insuffciency | pre-eclampsia

Question 38

what are the differences in presentation between placenta insufficiency and pre-eclampsia?

Answer 38

both have poor growth / development of foetus, but pre-eclampsia has maternal symptoms AS WELL

Question 39

what are the maternal symptoms of pre-eclampsia?

Answer 39

high blood pressure, sometimes with fluid retention, proteinuria

Question 40

what happens to the spiral arteries in pre-eclampsia?

Answer 40

inadequate modification of vessel wall | invasion not enough