Anatomy of placental development
trophoblast on outside and pleuriblast on insidetrophoblast contributes to embryonic aspect of placenta, and pleuriblast is what develops into embryo and amnion
development process of blastocyst (just implanting)?
Embryonic disc forms, which will develop into the amniotic cavity and yolk sac cavityinner cell mass (pleuriblast) develops into a couple of layers- hypoblast (yolk sac) and epiblast (amniotic sac)chorion starts to develop (placenta, invading with finger like structures), yolk sac becomes more apparent, and amniotic cavity becomes larger and pushes its way out into space.Other structure becoming apparent is the stalk of mesoderm tissue - connects all the the tissues and eventually the fetus to the developing placenta. Also has the allantois. becomes the umbilical cord.
where does the umbilical cord come from?
the mesoderm stalk, with the allantois in it as well
what is the hypoblast and epiblast?
differentiated from pleuriblast.hypoblast is nearest to the lumen, epiblast is nearest to the uterine walljust after trophoblast has invaded into decidual tissue, and differentiated into syncytiotrophoblast and cytotrophoblast (and completely covered by decidual tissue), we see further differentiation of two tissues, where the hypoblast develops into primitive yolk sac, and the epiblast develops into amniotic cavity
where does the primitive yolk sac come from?
the hypoblast - all animals have it
where does the amniotic cavity come from?
the epiblast
where is the Chorion found and what does it come from?
comes from trophoblast, forms placental plate and also surrounds outside of fetus and amnion. Also contributes to placental tissue.in birds/reptiles - gas exchange function; mammals - forms the placenta (only mammals)
Yolk sac function in birds vs mammals ?
• Yolk sac: birds/reptiles - external gut function; source of nutrients for animals in eggmammals - vestigial/ contributes to embryonic vascular system - part of blood vessels of embryo.
Allantois in birds/reptiles vs mammals
Allantois: birds/reptiles - waste disposal sac; mammals - part of the umbilical cord as development happens
Amnion in birds/reptiles vs mammals
Amnion: birds/reptiles/mammals - forms a fluid-filled shock absorbing sac around the embryo (more important in mammals).- same function in birds/reptiles AND mammals- the only one
steps of development of placenta as embryo develops into a fetus?
1 week after fertilisation, just after implantation, see two layers (hypoblast and epiblast) of inner cell mass differentiating, and trophoblast also differentiates (syncytiotrophoblast (weird cells that don;t have boundaries, which leads the invasion into the decidual tissue through epithelial layer) and cytotrophoblast, which remain as individual cells). Aim is to reach maternal capillaries for nutrient exchange (not blood exchange).extensive invasion by syncytiotrophoblast, which is controlled by decidual tissue (otherwise leads to hemorrhage).
how are the syncytiotrophoblasts so invasive?
number of mechanisms, but a key one = Matrix Metalloproteases (MMPs). Breakdown ECM/ cellular membranes for invasion
how is invasion controlled?
Tissue inhibitors of metalloproteinases (TIMPs) from decidual tissue- inhibit actions of Metalloproteases (MMPs). Breakdown ECM/ cellular membranes for invasion
what are two different types of nutrition ?
haemotrophic nutrition when invading trophoblast begins to make contact with maternal blood vessels- nutrition across blood supplyhistiotrophic nutrition- nutrition from the mucoid secretions (from luteal stage/ secretory stage)- enough to nourish embryo until it can establish haemotrophic nutrition
week 2 in development: Syncytiotrophoblast & cytotrophoblast growth?
develpment of the two types of trophoblast cells- pink = syncytiotrophoblast (developing the most- fingerlike projections and forms some spaces- lacunae) and note Cytotrophoblast.further vasculation from maternal, which fills lacunae with blood. Lakes filled with blood- increasing feature of blood supply to fetus and placenta- not blood vessels but more of a high volume/low pressure lake of blood surrounding fetus.Also see development of yolk sac and amnion. Also cavity begins to fill with mesoderm tissue. Now have maternal blood in contact with trophoblast, and begin to move to Haematrophic nutrition, and mesoderm tissue fills cavity.Mesoderm tissue develops out of epiblast
week 3 in development: Chorionic villi form from syncytiotrophoblast?
begin to get structures called villi- pushing in to established syncytiotrophoblast spaces- at first cytotrophoblasts push in and makes projections into existing space that has been made by syncy, and mesoderm tissue fills up space behind that. Early villi- primary villi become more developed with mesoderm core and become secondary. Mesoderm tissue forms a type of substrate where fetal blood vessels can begin to develop in substrate of mesoderm.
when do primary villi becomes secondary?
when mesoderm fills in core
fetal blood vessels
arteries and veins, which push through mesoderm tissue, with a layer of cytotrophoblast around outside and maybe a thin layer of syncytiotrophoblast as well, but very thinned out (faint pink layer on outside).
what is a stem villi?
when fetal vessel is so well developed that they push through, and cytotrophoblast cells attach to decidual layer on the far side of lacunae, is what is called a stem villi.
what are the different stages of Villus maturation?
syncytiotrophoblast fills space more generally. primary villi with cytotrophoblast filling in space madesecondary villi when mesoderm makes core inside of this. tertiary villi when fetal blood vessels develop inside of that.If it anchors itself to decidual cells on far side = stem villisyncytiotrophoblast becomes very thinned out.note in fetus, deoxygenated blood in the arteries and oxygenated blood in veins because oxygenated blood comes from this exchange.
cross section of tertiary villi?
0
How does the trophoblast remodel maternal blood vessels?
into high volume, low pressure lake like structures- all the trophoblasts doing.slowly invading out.some of the trophoblast manages to work independently- extravilli trophoblast, migrating its way across existing blood vessels, converting them into large diameter, low pressure- not connected to embryo but converts blood vessels.The vessels lose their ability to vasoconstrict so cease to function as blood vessels, but become large, low pressure structures
function of "Extravillous" trophoblast (EVT)?
migrates along maternal spiral arteries, dilating them and converting them to a low pressure, high capacity passage. The vessels lose their ability to vasoconstrict
Metabolic exchange at villi
spaces are filled with highly oxygenated blood from the mother, and the mature villi (stem villi).Sprial arteries feed the large, low pressure system with veins that drain them as well
8-12 weeks features: Chorion well defined; amnion and the amniotic cavity surrounds fetus
chorion forming a placental structure, along with maternal decidual cells with amnion and amniotic cavity surrounds an identifiable fetus.villi system very identifiable have the chorion frondosum (carpet like appearance) and chorion lavae (smooth like structure with amnion facing into cavity of uterus).so a smooth and rough part
what is the chorion frondosum?
the functional part of the placenta with all the villi - villi structure with a carpet like appearance
what is the chorion laeve?
smooth like structure with amnion facing into cavity of uterus
3-4 months: Placenta well established; umbilical vessels established
also don't really have a cavity outside the chorion anymore- become so large its pushed right up walls of uterus. can still identify decidua interacting with placenta. chorion / placenta becomes a plate-like structureamnion fused with chorion; uterine cavity obliteratedumbilical cord has 2 arteries and a vein
how many arteries and veins does the umbilical cord have?
2 arteries and 1 vein
Hormones of pregnancy: progesterone- role?
absolutely essential for pregnancy maintenance- keeps uterus in secretory state•prevents uterine muscle contraction •supports development of mammary gland tissuekeep going up throughout pregnancy to about 300progesterone made by corpus luteum and syncytiotrophoblast after a month or two-therefore the CL becomes redundant after 5-6 weeksi.e. as the placenta develops, maintainance of pregnancy becomes independent from the ovary and pituitary
Hormones of pregnancy: oestrogens, lactogens, growth hormones- where are they produced from?
The placenta also produces: •oestrogens (mostly oestriol) •placental lactogen •growth hormone variantsOestriol levels are therefore an indicator of fetal and placental health
what hormones does the placenta produce?
•oestrogens (mostly oestriol) •placental lactogen •growth hormone variants•progesterone
can the placenta produce androgens?
no- the fetal adrenal and liver does this from progesterone which is produced by the placenta doesnt have enzyme to make androgenOestriol levels are therefore an indicator of fetal and placental health (because oestriol is made from androgens)
function of Oestrogens during pregnancy?
Oestriol levels are therefore an indicator of fetal and placental health- increase blood flow to placenta- increase myometrial hypertrophy and hyperplasia - increase maternal prolactin production (lactation)- support mammary duct development (in breast)
variations of placental formation- bilobes placenta- battledore placenta
Bilobed placenta Placenta with two equal-sized lobes connected by a thin bridge. No identified risks.Battledore placenta Umbilical cord is attached at the margin off to the side. Occurs in up to 10% in singleton pregnancies and up to a third of twin pregnancies. May effect placental function/fetal growth because fetal blood vessels can't really all connect from the other side- only part of placenta really used- restricted growth?.
what is Placenta Increta?
an abnormality of placental formationPlacenta penetrates into uterine myometrium muscle- only meant to invade into basalis layer of endometrium17% of all placental abnormalities
what is Placenta Percreta?
Placental villi penetrate the myometrium and through to uterine serosa.advanced form of Placenta Incretacan lead to hemorrhage5%
what is Placenta Accreta?
Abnormal adherence, with absence of decidua basalis. Risk factors: prior cesarean section Detection by ultrasound (usually only in late pregnancy)75-78%
what is placenta previa?
abnormality of placenta placement normally attached to side, but can be variations. placenta previa is where it is down at base of uterus- can block cervixAttachment of placenta to lower uterus, blocking cervix Risk factors: multiparity; prior cesarean section Symptoms: painless bleeding in any trimester May require cesarean delivery
Different placental types of different species
Human and mouse have discoids placentasOther species have different shapes - cotyledons are lots of disc like onesZonary = circles around babyDiffuse = like lots of cotyledons
Maternal immune recognition of pregnancy- how is a fetus not rejected by the immune system?
Despite the fact that the uterus can mount an immune attack against bacterial infection, the "foreign" component of the fetus does not usually become a target for cytotoxic T-lymphocytes.
why does the "foreign" component of the fetus does not usually become a target for cytotoxic T-lymphocytes?
The trophoblast/placenta has features that are likely to minimize an immune response, creating an immunologically privileged site for the fetus. e.g. - Lack of normal MHC antigens? - Syncytiotrophoblast lacks extracellular spaces, which limits the immune cell exchange between the embryo and mother
Which of the following statements is correct? A. Tissue inhibitors of metalloproteinases (TIMPs) drive invasion of the trophoblast while matrix metalloproteases (MMPs) restrain this process. B. The syncytiotrophoblast invades the uterine wall, establishing the maternal-fetal interface. C. The cytotrophoblast invades the uterine wall, establishing the maternal-fetal interface. D. The decidua invades the uterine wall, establishing the maternal-fetal interface.
pretty sure B. The syncytiotrophoblast invades the uterine wall, establishing the maternal-fetal interface.