8.1: Reproductive system (embryo, lecture) 1 Flashcards
in very early embryonic development, what takes precedence?
establishment of the placenta
why is establishment of the placenta so important?
ensures support for the pregnancy
what happens in week two? (the week of twos)?
differentiation:
2 distinct cellular layers emerge
what are the outer cell mass of week 2? (2 of 2)
outer cell mass:
syncytiotrophoblast
cytotrophoblast
what do the inner cell mass form in week 2?
bilaminar disk
what are components of the bilaminar disk?
inner cell mass:
epiblast
hypoblast
what are the cavities early on (1 week post fertilisation)?
at first blastocyst cavity (blastocoele) - within trophoblast
then amniotic cavity appears within the epiblast cellular layer
what happens at around day 6 of fertilisation?
syncytiotrophoblast invade the maternal uterine epithelium layer
(breaching of endometrium)
what happens post implantation?
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
what has happened by the end of week 2?
conceptus has implanted
embryo and its cavities (amniotic cavity and yolk sac) suspended via CONNECTING STALK within chorionic cavity
what does the connecting stalk suspending the embryo and its cavities become?
modified to become umbilical cord
communicate between embryo and internal maternal circulation
what is the amniotic cavity arising from epiblast of embryoblast also known as?
amion
where the embryo grows
what are the 3 major cavities during embryonic development?
yolk sac
amniotic cavity
chorionic cavity
as the embryo develops what happens to the yolk sac, amniotic sac and chorionic sac?
yolk sac disappears
amniotic sac enlarges within the chorionic sac
how can you describe implantation?
interstitial (occupies interstitium space) as uterine epithelium is breached
where does the conceptus implant?
within the stroma
what happens to the placental membrane as the foetus develops?
becomes progressively thinner as NEEDS of foetus increases
how is the human placenta?
haemomonochorial
what is haemomonochorial (human placenta)?
1 layer of trophoblast ultimately separates maternal blood from foetal capillary wall
(maternal blood bathing: trophoblast + foetal endothelium)
what are the 3 aims of implantation?
- establish basic unit of EXCHANGE
- ANCHOR the placenta
- establish MATERNAL blood flow within placenta
how is basic unit of EXCHANGE between mother and foetus achieved?
via primary, secondary and tertiary villi
what are primary villi in basic unit of exchange from implantation?
early finger-like projections of TROPHOBLAST (outer cell mass)
(cytotrophoblast surrounded by syncytiotrophoblast)
what are secondary villi in basic unit of exchange from implantation?
INVASION of MESENCHYME into cytotrophoblast core
now mesoderm core within cytotrophoblast, surrounded by syncytiotrophoblast
what are tertiary villi in basic unit of exchange from implantation?
invasion of mesenchyme core by foetal vessels
now vessels within mesenchyme < cytotrophoblast < syncytiotrophoblast
how does implantation anchor the placenta?
establishment of the outermost cytotrophoblast shell
what is the cytotrophoblast shell (anchor placenta)?
the external layer of cytotrophoblasts from the foetus that is found on the maternal surface of the placenta
what are the 2 major excessive implantation defects?
ectopic pregnancy
placenta praevia
what is ectopic pregnancy?
implantation at site other than uterine body (most commonly fallopian tube)
although can be peritoneal or ovarian
can v quickly become life-threatening emergency
what is placenta praevia?
implantation in lower (1/3) uterine segment
can cause haemorrhage in pregnancy
requires C-section
why does placenta praevia require C-section?
placenta grows across internal os
internal os completely occluded by placenta
birth canal cannot function, therefore requires c-section
histology of the endometrium: how does endometrium prepare for implantation? (cells and arterial blood supply)
‘pre-decidual cells’
elaboration of spiral arterial blood supply
(endometrium prepared for implantation)
what is decidualisation?
the decidual reaction provides the balancing force for the invasive force of the trophoblast
(syncytiotrophoblast invade endometrium - uterine lining)
a response of maternal cells
where are desidual cells present?
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.)
describe the process of desidualisation within ectopic pregnancy
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
why is remodelling of the spiral arteries necessary?
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)
histologically, where are decidual cells found?
surrounds myometrium like a cuff
what are the 2 major incomplete invasion defects?
placenta insuffciency
pre-eclampsia
what are the differences in presentation between placenta insufficiency and pre-eclampsia?
both have poor growth / development of foetus, but pre-eclampsia has maternal symptoms AS WELL
what are the maternal symptoms of pre-eclampsia?
high blood pressure,
sometimes with fluid retention,
proteinuria
what happens to the spiral arteries in pre-eclampsia?
inadequate modification of vessel wall
invasion not enough
