Placentation and implantation Flashcards
what are the 3 stages of the mother foetus link
invasion
decidualisation
placentation
what is decidaulisation
endometrial remodeling: secretory transformations of the uterine glands, influx of natural killer cells and vascular remodeling
what is the embryoninc placenta formed from
outermost layer of trophoblast- the chorion
what is the maternal placenta derived from
the endometrium underlying the chorion
describe blood flow in the placenta
chorionic villi extend from the chorion to the endometrium. villi have cappiliaries
endometrium changes so that it forms a pool of maternal blood around each villi
what is the blood supply of the placenta
uterine artery and vein from the mother
umbilical arteries and veins from the foetus
what is the zona pellucida
the membrane surrounding the ovum before implantation
when does the blastocyst leave the zona pellucida
day 7
is bathed in uterine secretions for 2 days
what hormones are involved in attachment and implantation
progesterone prepares the uterine environment and increases glandular tissue
oestrodiol releases glandular secretions
describe implantation
syncytiotrophoblast cells flow into the endometrium and erode the maternal capillaries which bleed into the spaces.
oedema, glycogen synthesis and increased vascularisation(decidualisation).
what is the term for the pregnant endometrium
decidua
what do the villi form from
syncytiotrophoblast
describe the features of villi
contain a fetal capillary loop with a slow flow rate
villi become localised at the embryonic pole
when is maternal circulation functional by
10-12 weeks
hence the first trimester embryo is dependent on uterine tissues
what makes up the placental membrane
fetal capillary endothelium
basement membrane
cytotrophoblast
syncytiotrophoblast
what might cause early pregnancy losses
lack of hormonal support (luteal deficit)
endometrium is too thin,
what are the components of a secondary villi
an inner core of extraembryonic mesoderm
a middle cytotrophoblast layer
an outer syncytiotrophoblast
what is the function of HCG
maintains progesterone secretions from the corpus luteum until the placenta can synthesise its own progesterone
when is hCG secreted
when the embryo implants at 8-10 weeks by the syncytiotrophoblast
when is hCG measurable
7-8 days post conception
by urine tests after 2 weeks
what is the function of hCG
mimics LH
supports steroid synthesis of the CL
prevents menstruation and follicular development
prevents menstruation and follicular development
stimulates leydig cells to produce testosterone in male foetuses
describe the development of the placenta
month 1- villus formation
month 2 - increasing surface area and circulation
month 3- grows
when does the placenta thin
20 weeks with loss of the cytotrophoblast
what is the renal function of the placenta
regulates fluid volume and disposes of waste metabolites
what is the endocrine function of the placenta
synthesises steroids and proteins that affect both foetal and maternal metabolism
what is the function of progesterone in pregnancy
increases throughout pregnancy
suppresses follicular growth and ovulation
suppresses the immune response
maintains the endometrium
how long is the CL required for
5 weeks which is the point at which the placenta is able to secrete all steroid hormones
what substance is the substrate for progesterone
maternal cholesterol
what is the main type of oestrogen in pregnancy
oestriol
what is the function of oestriol
stimulates growth of myometrium and breast ducts
along with relaxin, relaxes and softens maternal pelvic ligaments and pubic symphysis which allows uterine expansion
stimulates LDL cholesterol uptake and p450 enzymes which helps to synthesise progesterone
provides an indication of the function of the placenta
how are nutrients exchanged across the placenta
water and electrolytes diffuse freely
glucose is via facilitated diffusion
amino acids are via active transport
lipids cross as free fatty acids
describe gas exchange
foetal hb has a greater affinity for o2 than maternal
towards the end of pregancy placenta is less able to meet the demands
what might cause ectopic pregnancies
pelvic inflammatory disease
endometriosis
where are the vast majority of ectopics
ampulla/isthmus
where does attachment normally occur
posterior wall of fundus of the uterus
what are the features of ectopics
increasing in incidence - 1 in 150 approx
rupture of the uterine tube may cause fatal blood loss
symptoms may be confused with appendicitis
