Implantation and placentation Flashcards
what happens in the week of 2’s?
By 2nd week!>> Day 8
2 distinct cellular layers emerge from:
- outer cell mass
- – syncytiotrophoblast*
- – cytotrophoblast*
- inner cell mass becomes the bilaminar disk
- – epiblast*
- – hypoblast*
Define implantation & what day does it occur? how long does it take? when does it end?
early stage of preganancy in which conceptus adheres to the wall of the uterus (endometreium)
the uterine epithelium is breached and the conceptus implants w/ in the stroma
begins 6-7 days after fertilization!>> when endometrium is propper and ready
takes about 5 days and usually compeltes 12th day after ovulation (normally when the endomterium walls sloughs off)
why does the blastocyst have to wait an extra 1-3 days before it implants on the endometrium? what is keeping it alive until then?
after reaching the uterus, the developing blastocyst just chills there for extra 1-3 days before it implants…until then…it is nourished from the uterine endometrial rich glycoprotein secretion “uterine milk”
bc weyre waiting for the endometrium to be properly ready!
Describe the processes of implantation of the conceptus into the endometrium
describe the blastocyst structure!
what occurs by the end of the 2nd week?
the conceptus has implanted (not yet done with the process tho)
what does implantation acheive?
(explain the 3 different villi)
during implantation, trophoectoderm cells begin to differentiate to cellular subtypes that will characterize the placenta.
its gunna establish the major unit of exchange!
– primary villi: early finger-like projections of trophoblast
– secondary villi: chornionic extensions grows into primary villi
– tertiary villi: fetal BV form in the vill!
Implantation defects r characterized into 2 catagories, name them…
- Implantation in the wrong place
- Incomplete invasion (invasive element of implantation r incomplete!)
Implantation in the wrong place (2 conditions)
– Ectopic pregnancy
– Placenta praevia
cells of the endometrium r critically important for modulating the invasive reaction during implantation.
many of the enzymes released by the trophoblasts allows the the process of implantation to occur and allow access of conceptus into the endometrium!
these enzymes can be extremely invasive…so how does endomterium cope with it?
what does that tell u if u had ectopic pregnancy at a site where u dont have endometrium?…
The decidual reaction provides the balancing force for the invasive force of the trophoblast!!
in ectopic pregancy>> no decidua layer>> no control>> invasion can go right into the wall of the uterine tube and out into the pelvic cavity where uve got a larger room.
thats why its a life-threatening emergency!
Ectopic pregancy
where does it most commonly occur?
most common in fallopian tube
can be peritoneal as well
life threatening
Placenta previa
what can it cause?
implanatatin at lower uterine segment
if it crosses the internal os of cervix>> can cause hemmorhage in preganacy
birth canal is blocked>> requires C- section
what happens to the embryonic spaces during placentation? (yolk sac, amniontic sac, chorionic sac)
- yolk sac dissappears (pinches off and later become gut tube)
- amniotic sac enlarges
- chorionic sac is occupied by expanding amniontic sac! (amniotic sac keeps growing until it closed it up)
what is placentation?
formation of the placenta“flat cake”
a temporary organ that originated both from embryonic & maternal (endometrial) tissues.
the placenta is specialisation of what?
the placenta is specialization of the chorionic membrane
endometrium undergoes “decidual change”
describe it
when the conceptus implants the endometrium, via the continued release of progesterone, the endometrium cells SWELL further & store more nutrients.
these cells r now called Decidual cells and the total mass of cells r called decidua!
decidual reaction is “transformed epithelium”
what is a chorionic villi? chornionic frondosum?
explain the different villi made
major unit of exchange!
– primary villi: early finger-like projections of trophoblast
– secondary villi: chorionic extensions grows into primary villi
– tertiary villi: fetal BV form in the vill!
Describe the structure of the placenta and its explain its adaptation for the exchange of materials between fetal and maternal blood
-has a mass of tree-like placental cotyledons called “villi” which r bathed in maternal blood!
blood enters space btw villi (intervillus space) through high-flow maternal spiral (endometrial) vessels.
fetal vessels r located w/ in the cotyledons (villi)
cytotrophoblast surrounding tip of each villi will make a “outer-trophoblastic shell”
The outer layer of the placental villae is coated by a syncytiotrophoblast.
The syncytiotrophoblast is directly bathed in maternal blood in the mature placenta
The______________is directly bathed in maternal blood in the mature placenta
The syncytiotrophoblast is directly bathed in maternal blood in the mature placenta
Structure of the chorionic villus and thinning of placenta over time (in 1st trimester & 3rd trimester )
1st trimester villus >> thick barrier
3rd trimester villus >> thin barrier
Describe the arrangement of fetal blood vessels within the placenta
- 2 umbilical arteries>> Deoxygenated blood from fetus to placenta
- 1 umbilical vein >> Oxygenated blood from placenta to fetus
umbilical A. winds around the vein
what is the function of the cytotrophoblast surrounding the villia?
it acts as a stem cell layer for the syncitotrophoblast.
allows it to keep growing > so we can build room for growth
(cytyotrophoblast is a specilaised version of the syncitiotrophoblast)
What tissues constitute the placental barrier at the 3rd trimester?
Only syncytiotrophoblast & fetal capillary endothelium
(its gotten thinner cuz baby metabolic needs r high and we need good transfer)
what gives the placenta its glossy appearnece?
the amniotic transparent memebrane
Placental functions
list hormones secreted by placenta?
- secretes progesterone & estrogen
- HcG & HcS
Human Chorionic Gonadotrophin (hCG)
produced by? how many days after fertilization is it secreted for? how long is it secreted for? function?
- produced during the first 2 months of pregnancy
- supports the secretory function of CL
- produced by syncytiotrophoblast therefore is pregnancy specific
- excreted in maternal urine therefore used as the basis for pregnancy testing
- used to diagnose trophoblast disease
when does placenta take over the function of the CL
by the 11th week (1st trimester)
what r the placental hormones that influence metabolism?
- Progesterone
- hCS/hPL
how does progesterone influence metabolism?
how does hCS/hPL influence metabolism?
In early pregnancy, progesterone stimulates appetite and promotes maternal deposition of fat
How is this beneficial to the mother in later pregnancy and after birth ?
Maternal preparation
- e.g. breast growth, and also may provide a reserve for later pregnancy when fetal demands are greater.
- In later pregnancy mom relies on FAT for energy stores isntead of glucose! ( cuz baby used up all the glucose!)
Explain the factors influencing the passive diffusion of substances across the placenta
• Simple diffusion
– molecules moving down a concentration gradient
- water
- electrolytes
- urea & uric acid
• gases
Facilitated diffusion
– applies to GLUCOSE transport
why is adequate blood flow essential to placenta? (in term of transport functions of placenta)
bs gas exchange is FLOW- limited! not diffusion limited!
Identify the major substances which are actively transported across the placenta
specific“transporters”expressed by the syncytiotrophoblast
– amino acids
– Fe2+
– vitamins
Explain the function of the placenta as a provider of passive maternal immunity to the neonate
fetal immune system is very immature, it takes weeks to monthe for the baby to develop a good immune system!
mum comes to rescue!
ONLY IgG goes to baby via recepter mediated proess!!
IgG concentrations in fetal plasma exceed those in maternal circulation !! olaaaaa
Explain the maternal physiological adaptations to pregnancy
what r teratogens?
an agent or factor which causes malformation of an embryo. (can cross placenta)
what is the most senstive period in teratogenesis? why?
Embryonic period
time where we r building all the imporant organs and structure in the body!
what happens if there is rhesus incompatibility btw mum and fetus?
MTD antibodies can cross placenta (bc they r from an IgG class)
and can cause hemolytic disease in baby!
this is why rhesus testing is tested out!
name some harmful substances that can cross placenta
• thalidomide
– Limb defects
• Alcohol
– FAS > fetal alchoholic syndrome
- ARND> Alcohol-Related Neurodevelopmental Disorder
therapeutic drugs
– Anti-epileptic drugs
– Warfarin
– ACE inhibitors
drugs of abuse
– Dependency in the fetus and newborn
• maternal smoking
what r some theruputic drugs that can cross the placenta?
- warfarin
- antiepileptics
- ACE inhibitors
How does alcohol cross the placenta? What implications does this have for the development of a baby whose mother drinks significantly during pregnancy?
By diffusion – lipid soluble
Possible cause of Fetal Alcohol Syndrome in which the maternal (mis)use of alcohol leads to a fetus of low weight and with growth retarded (potentially with mental retardation, head and facial abnormalities).
what is the baby infected with?
cytomegalovirus!
can cause fetal death
some common pathogens related to babies?
- listeria monocytogenes
- cytomegalovirus
In the third stage of labour, what tissue of maternal genetic origin is shed with the afterbirth?
The decidua
What effects would you expect maternal smoking to have upon the placenta? What effect may this have upon the baby?
May reduce placental blood flow and growth.
Poorer fetal nutrition will reduce birth weight, by on average, 200g.
Draw a graph showing the levels of hCG in the blood of a woman throughout pregnancy and into the immediate post-natal period.
Late pregnancy is associated with venous distension and engorgement. What factors contribute to it?
- smooth muscle relaxation by progesterone.
- Mechanical pressure from the uterus compressing the IVC may increase lower limb venous pressure, but only when mother is recumbent.
why does insulin resistence occur in mum? what makes this happen?
to make sure that glucose is availble for the fetus!
HCS
what happens to tidal volume in pregnancy?
Increases!
what happens to maternal respiratory rate?
UNCHANGED!
what happens to GFR?
increases by 55%
