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Repro Week 3 > LM 15.2: Normal Placenta > Flashcards

LM 15.2: Normal Placenta Flashcards

1
Q

what structure is the placenta derived from?

A

trophoblasts

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2
Q

how many umbilical arteries and veins are there?

A

2 umbilical arteries and 1 umbilical vein that go to the placenta from the baby via Wharton’s jelly

arteries bring deoxygenated blood from the fetus to the placenta which returns to the fetus via the umbilical vein

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3
Q

where do uterine arteries originate from?

A

they started as the late luteal phase spiral arteries that now continue to develop due to presence of a pregnancy

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4
Q

do maternal and fetal blood mix?

A

no!

there is nutrient exchange via diffusion via the trophoblasts, arteries and veins of the baby in the chorionic plate aka the placenta!

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5
Q

what is the placenta?

A

fetal tissue attaching and intimately juxtaposed to maternal tissue

it’s an alloimmunografTT the uterus allows foreign DNA to attach without rejection while maternal blood is flowing over the fetal syncytiotrophoblasts on the outside of the villi

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6
Q

when does implantation occur>

A

day 6 after conception

the blastocyst comes into contact with endometrium, which is receptive due to absence of antiadhesive glycoprotein which is normally produced later in the luteal phase of the menstrual cycle

the blastocysts then adheres to the decidua and then the blastocyst’s trophoblasts invade the decidua, the inner 1/3 of the myometrium and uterine vasculature

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7
Q

trophoblasts differentiate into which 2 cells?

A
  1. syncytiotrophoblasts

2. cytotrophoblasts

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8
Q

what are syncytiotrophoblasts?

A

one of the 2 cell types that embryonic trophoblasts differentiate into

  1. multinucleated
  2. outer later
  3. transport functions of the placenta
  4. synthesizes hormones
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9
Q

what are cytotrophoblasts?

A

one of the 2 cell types that embryonic trophoblasts differentiate into

  1. mono nucleated cells
  2. inner layer
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10
Q

what are the 2 locations that the embryonic trophoblasts differentiate into?

A
  1. villous trophoblasts create the chorionic villi

some of these become the anchors of the placenta to the basal plate and do not go deeper than Nitabuch’s layer

  1. extravillous trophoblasts—these can penetrate the myometrium

endovascular trophoblast penetrate the spiral artery lumens and replace the endothelial lining and smooth muscle of the arterial wall

interstitial trophoblasts invade decidua and myometrium as well as surround maternal spiral arteries

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11
Q

what are chorionic villi and what is their blood supply?

A

chorionic villa are supplied by the branching temrinal vessels from the umbilical cord that form the base of the fetal side of the placenta

the villi are located on the maternal side of the placenta and are:

  1. lined by ctyotrophoblasts
  2. outside of the villi are covered by syncytiotrophoblast
  3. provide a large surface are of contact between the villi and maternal blood allowing gait and nutrient exchange
  4. maternal blood has direct contact to the syncytiotrophoblast layer
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12
Q

what is a placental cotyledon?

A

a collection of chorionic villi from a main stem villi and supplied by a chorionic artery and drained by a vein

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13
Q

what is the progression of villi development of the placenta?

A

week 1: primary villi develops with a cytotrophoblast core and syncytiotrophoblast sheath

week 2: secondary villus develops that now also has an extramebryonic mesoderm core within the cytotrophoblast layer

week 3: tertiary villi develop that has vessels forming in the mesenchyme aka the umbilical artery and vein branches are spreading into the villi from the chorionic plate

week 4 and beyond: stem villi develop and anchor the villi to the maternal basal plate; there is continued development of the terminal villi

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14
Q

what happens to the spiral arteries during pregnancy? how do they interact with the placenta?

A

spiral arteries of the uterus are lined by extravillous cytotrophoblasts that remodel the arterial wall to remove any decrease in flow of blood into the intervillous space aka they dilate the arterial opening into the intervillous space!

the lumen of the artery is actually increased 5-10 fold, making it a low resistance, large bore vessel.

it does not have contractile properties making it also unregulated

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15
Q

what are the characteristics of the placenta at term?

A
  1. fundal/posterior position in the uterus
  2. cephalic presentation of the fetus (head first)
  3. central insertion of cord into placenta
  4. fetal surface of placenta is smooth and covered by amnion
  5. maternal surface isn’t smooth
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16
Q

how big is a mature placenta?

A

diameter: 20-22 cm

mean weight: 470 gms

thickness: 25 mm

total VILLOUS surface area is 12-14 m2

that’s 11’4” X 11’4” to 12’3” X 12’3”!!

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17
Q

what does the maternal surface of the placenta look like?

A

maternal surface of the intervillous space has developed septa that correspond to the clefts of the cotyledons and derive from the cytotrophoblast of the basal plate

the septa grow into the inter villous space but not across; they probably but help with a more optimized, directed blood flow within the inter villous space

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18
Q

what covers the fetal surface of the placenta?

A

amnion

it covers the fetal surface and the umbilical cord

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19
Q

what is the decidua basalis?

A

it’s the endometrium of pregnancy; the basal plate contains the decidua basalis
it lies directly beneath the implanted blastocyst and is influenced by the invading trophoblastic tissue

it’s triggered by hormones and factors secreted by the blastocyst and it’s central to the allograft of pregnancy

because of the implanted blastocyst, the decidua basalis undergoes the most change via spiral artery growth and invasion

it is shed during the weeks after delivery

20
Q

how does the decidua basalis change after implantation?

A

during the luteal phase of the menstrual cycle, the spiral arteries have become more developed, anticipating implantation of the blastocyst

with implantation, the spiral arteries/arterioles are invaded by trophoblasts

a shell of the original arterial wall remains having lost its endothelial cell and smooth muscle layers

the spiral arteries/arterioles become unregulated compared to normal arteries; they do not respond to vasoactive agents.

note: interestingly, the fetal chorionic blood vessels do have smooth muscle and do respond to vasoactive agents.!

21
Q

what are the 3 parts of the decidua?

A
  1. decidua basalis
  2. decidua capsularis
  3. decidua parietalis
22
Q

what is the decidua capsular?

A

it lies over the implanted blastocyst creating a barrier between blastocyst and endometrial cavity

23
Q

what is the decidua parietals?

A

it lines the rest of the endometrial cavity other than where the blastocyst is implanted

24
Q

what is the decidua vera?

A

it’s created when the enlarging pregnancy causes the decidua capsularis and decidua parietalis to fuse

formation of the decidua vera obliterates the uterine cavity

25
Q

what is the Nitabuch layer?

A

it’s the line that demarcates the trophoblastic invasion from the blastocyst to the decidua basalis

it’s an area of fibrinoid degeneration between trophoblasts and decidua basalis

it is defective or absent in placenta accreta spectrum disorder

26
Q

what is the chorion frondosum?

A

when the blastocyst implants, villi persist where contact of decidua basalis occurs, to form the chorion frondosum where the villi/placenta will develop

chorionic villi that are not involved with the decidua basalis, undergo degeneration due to no longer receiving vascular support which creates the chorion leave

27
Q

what is amnion?

A

an avascular fetal membrane lining the amniotic sac –> no blood vessels, lymphatics, smooth muscle or nerves

it’s lined by a single layer of cuboidal epithelium –> so the amnion lines the amniotic sac which contains the amniotic fluid

as early as 10 days after fertilization, the amniotic cavity is present as a space between the trophoblastic tissue and the embryonic disc and as the amniotic cavity grows, it surrounds the entire embryo and body stalk

28
Q

what is the function of amniotic fluid?

A
  1. fetal movement; creates space for the fetus to move which is key for neuromusculoskeletal development
  2. fetal breathing for normal lung development
  3. fetal swallowing of AF is needed for development of GI tract
  4. umbilical cord flow integrity; prevents compression of the vessels within the cord
  5. bacteriostatic function
29
Q

when does fetal urine production start?

A

8-11 weeks gestation

30
Q

what is the composition of amniotic fluid?

A

it’s hypotonic compared to fetal and maternal osmolality

98% water

contains exfoliated fetal cells/DNA, proteins, etc.

31
Q

how much amniotic fluid is there normally by term?

A

800 cc

32
Q

where does the umbilical cord originate from?

A

the caudal region of the developing embryo

final development leaves 2 arteries and 1 vein in the umbilical cord

it’s located in the middle of the placental disc but can also arise from near the periphery or even be located completely separate from the disc

33
Q

what is Wharton’s jelly?

A

a tissue that provides protection to the vessels and substance to the cord to prevent compression from outside forces

34
Q

how is the placenta expelled?

A

once the baby is delivered, the uterus contracts down due to loss of uterine cavity volume

with that contraction, the area of placental attachment decreases relative to the area of the placenta leading to shearing, causing placental detachment

placenta is expelled and as it exits, peeling off the chorion from the uterine cavity, resulting in complete expulsion of placenta and its attached membranes

35
Q

which hormones does the placenta make?

A
  1. steroids
    ex. 17β estradiol, estriol, and progesterone
  2. proteins
    ex. hCG, hPL, adrenocorticotropin, GnRH, TRH, growth hormone variant, neuropeptide y, inhibin, activin

components for production of these steroids and proteins can cross the placenta to or from the maternal or fetal circulation or originate in the placenta

the placenta produces the most steroid and protein hormone in amount and diversity of any human organ

36
Q

where does progesterone come from during pregnancy? what is its function?

A

progesterone is initially produced by the corpus luteum under stimulation by βhCG produced from the implanted blastocyst –> placental production begins at 7 weeks and is the primary source by 10 weeks

production is independent of health status of placenta or fetus

  1. required for successful preparation of endometrium and implantation
  2. may contribute to suppressing maternal immunologic response to fetal tissue
  3. serves as a substrate for the fetal adrenal gland to produce gluco- and mineralocorticoids
37
Q

where does estrogen come from during pregnancy?

A

first 5-6 weeks: corpus luteum

after 5-6 weeks: placenta

precursors are from outside the placenta

38
Q

what do estrogen levels tell you about the pregnancy?

A

estrogen levels can reflect the health of the fetus!

39
Q

what does estrogen influence during pregnancy?

A
  1. progesterone production
  2. uteroplacental blood flow
  3. mammary gland development
  4. fetal adrenal gland function
  5. stimulates maternal and trophoblastic renin-angiotensin systems resulting in increase in maternal blood volume
  6. has vasodilatory effect on uteroplacental blood flow
40
Q

what is hCG?

A

a glycoprotein related to LH, TSH, FSH—they all share a common α-unit

it is produced almost exclusively in the placenta but there are low levels produced in the fetal kidneys

αhCG production is related to placental mass –> there is very little free β hCG; measurement of β hCG is in its combined form with αhCG

41
Q

when does hCG production peak?

A

secretion of total hCG (α and β hCG combined form) production peaks at 8-10 weeks

42
Q

what is the function of hCG?

A
  1. maintains progesterone production by the corpus luteum until placenta can take over
  2. stimulates fetal testicular testosterone secretion

it acts as LH surrogate stimulating Leydig cell replication and synthesis of testosterone–> promotes male sexual differentiation

43
Q

what is hPL?

A

human placental lactogen aka chorionic growth hormone aka chorionic somatomammotropin

it’s produced early in gestation prior to 6 weeks by cytotrophoblasts but then overall production is predominantly by syncytiotrophoblasts

secretion rate noted to be proportional to placental mass up to about 34-36 weeks

96% homologous to prolactin

44
Q

what does hPL do?

A
  1. promotes maternal lipolysis resulting in increased free fatty acids circulating aka an energy source for maternal and fetal needs
  2. aids maternal adaptation to fetal energy requirements by increasing insulin resistance allowing more glucose to cross over to fetus.
  3. hPL increases beta cell proliferation
  4. prepares mammary glands for lactation
45
Q

where is alpha fetoprotein produced?

A

yolk sac

up till about 12 weeks then later largely from the fetal liver

AGP is metabolized by the maternal liver

46
Q

what do elevated AFP levels indicate?

A

it’s highly concentrated in the fetal CNS so any malformation of CNS resulting in less tissue between fetus and amniotic fluid results in increased levels in AFP and resultant increased levels in maternal blood

elevated maternal serum AFP is associated with:
1. CNS malformations

  1. multifetal gestation
  2. preterm birth
  3. pre-eclampsia risk
  4. fetal demise
47
Q

what are the 4 main functions of the placenta?

A
  1. metabolism
  2. transport of oxygen, cO2, nutrients, waste
  3. endocrine signaling
  4. preventing fetal allograft rejection

Repro Week 3 (26 decks)

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