8. Placental function and dysfunction (workbook) Flashcards
what does the placenta contain?
both materal and fetal components
what does a good placenta determine?
a good pregnancy
what does the placenta represent?
the surface interface between the mother and developing child
what is the function of the placenta?
the structure through which nutrients are supplied from the mother and waste is removed from the embryo / foetus
when does development of the placenta begin?
soon after fertilisation at compaction
from which cells does the placenta develop?
trophoblast
outer cell mass destined to develop into the structures that support the embryo / foetus during pregnancy
what is the embryo / foetus enclosed by?
the amnion and chorion membranes in a protective sac
what does the placenta develop as?
a specialisation of the outer membrane, the chorion
when does the development of the placenta as the chorion begin? (specialised outer membrane)
begins as implantation gets underway
what does the chorion take the form of? (post-fertilisation)
finger-like projections: chorionic villi
what are chorionic villi?
functional units of the placenta
what do chorionic villi represent?
point of exchange between the maternal and fetal circulations
what do chorionic villi consist of?
a vascularised core covered by 2 epithelial layers
how does materno-fetal exchange occur?
both simple and facilitated diffusion,
active transport,
receptor mediated endocytosis
what ensures materno-fetal exchange is efficient and simply regulated?
combined utero-placenta and feto-placental circulations
represent a counter-current supply
what does the placenta act as?
a selective barrier to the fetal circulation that regulates access to the fetal circulation
considerable protection from harmful agents
what is a flaw of the placenta as a barrier?
not complete, can be breached
how can the placental barrier be breached?
by simple ‘leakage’
Number of infectious agents may utilise existing transport systems e.g. HIV
Actively penetrate e.g. Treponema
Opportunistically exploit gaps in the epithelium
how can the placental barrier be breached?
by simple ‘leakage’
number of infectious agents may utilise existing transport systems e.g. HIV
what (else) is placenta responsible for?
Provision of passive immunity that affords immune protection in the neonatal period
Endocrine support of pregnancy
(nutrient supply + waste removal)
why does the placenta mature?
to meet the increasing demands of the growing fetus
what happens as the placenta matures?
it adapts by decreasing the interhaemal distance
how is the interhaemal distance decreased?
by thinning of the trophoblast layer (s)
Margination of the fetal capillaries of the core of the villi
Increasing the SA for exchange
how does the placenta increase the SA for exchange?
through increasing branch of villus tree
when is decreasing of interhaemal distance exaggerated?
in situations where the demand for transported materials or restriction on the maternal side leads to a deficit
when does the demand for transported materials or restriction on the maternal side lead to a deficit?
e.g. placentae from pregnancies in women who smoke / live at high altitude - have reduced interhaemal distances when compared to ‘normal’
(interhaemal distance decreased MORE than normal)
is there a limit to the decrease of interhaemal distance?
yes, can have circumstances when the placenta’s power of compensation is exceeded
what is placenta defect one of the major risk factors of?
intrauterine growth restriction
what does impaired fetal growth link to?
long-term adult health problems
what is impaired fetal growth linking to long-term adult health problems called?
Barker hypothesis
the fetal origins of adult disease
when is the placenta shed?
at parturition (birth)
what happens at parturition? (birth)
the massive blood supply to the implantation is shut down
what happens if the placenta fragments during labour?
can result in retained placenta which impairs shut-down of the utero-placental circulation
what happens if the shut-down of utero-placental circulation is impaired?
can cause serious post-partum haemorrhage
post birth
