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embryology > week 2: bilaminar disk and embryo annexes > Flashcards

week 2: bilaminar disk and embryo annexes Flashcards

1
Q

factors affecting successful implantation

A
  • 25% morphology
  • 25% kinetics
  • 50% genetics
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2
Q

immunogenic dilemma

A
  • systematic immunocompetence and protection vs. uterine immunotolerance
  • symbiosis between semi-allogenic individuals
  • how fetus avoids immune rejection remains paradox
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3
Q

factors preventing host-versus-graft rejection

A
  • fetal and maternal cells are physically separated from one another
  • embryo is antigenically immature: poor MHC molecules expression
  • maternal immune system is locally immunosuppressed
  • extracellular vesicles and microRNAs
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4
Q

chorionic gonadotropines

A
  • major role in LOCAL suppression
  • hCG produced by trophoblast suppress the immune reactions of maternal WBCs
  • embryo produced immunisuppressors
  • additional molecules
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5
Q

proliferation of trophoblast

A
  • stimulated by interaction with uterine mucosa
  • decidua: endometrium in pregnant woman
  • implantation occurs on the side of embryonic plate
  • trophoblast differentiates while invading the endometrium into syncytio-trophoblast and cyto-trophoblast in implanting blastocyst of 6 days
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6
Q

additional differentiation of ICM in blastocyst

A
  • epiblast: cylindrical epithelium like tissue
  • and hypoblast: flat epithelium like tissue
  • bilaminar disk
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7
Q

prechordal plate

A
  • not all cells of hypoblast are equal
  • a thickening of endoderm at the cranial end of primitive streak
  • origin of rostral cranial mesoderm
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8
Q

two cavities formed in the second week

A
  • amniotic cavity
  • yolk sac
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9
Q

primitive amniotic cavity

A
  • by 8 days the amniotic cavity has appeared within the epiblast
  • epiblast cells differentiate into amnioblasts that line cavity and form amniotic membrane
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10
Q

day 9 and primary yolk sac

A
  • by 9 days the embryo is completely implanted
  • hypoblast cells proliferate and migrate out over cytotrophoblast to form Heuser’s membrane around yolk sac and extraembryonic mesoderm
  • trophoblastic lacunae appear in syncytiotrophoblast which now completely surrounds embryo
  • point of implantation is marked by a transient coagulation plug in endometrial surface
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11
Q

formation of extraembryonic mesoderm

A
  • day 10-11: space between Heuser’s membrane and the cytotrophoblast fills with loosely associated extraembryonic mesodermal cells
  • 11-12: mesoderm expands between amnion and cytotrophoblast also
  • forms between embryo and yolc sac in CTB
  • initially continuous layer then spaces appear causing separation into two
  • splanchnopleuric (visceral) and somatopleuric (parietal) mesoderm
  • splanchno around yolk sac and embryo
  • somato lining the cytotrophoblast
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12
Q

which tissue forms extra-embryonic mesoderm

A
  • from hypoblast/contribution from trophoblast in humans
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13
Q

extra-embryonic cavity

A
  • squeezes the yolk sac
  • chorionic cavity:
  • ex-e coelom and medoserm
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14
Q

secondary yolk sac

A
  • primary yolk sac breaks up and is reduced to a collection of vesicles at the abemrbyionic end of the chorionic cavity
  • secondary (definitive yolk sac) is formed
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15
Q

trophoblast derivatives

A
  • syncytiotrophoblast erodes the endometrium, forms lacunae
  • cytotrophoblast provides additional cells to syncy
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16
Q

lacunae

A
  • fill with maternal blood
  • within a few days, as syncy erodes uterine vessels
  • finger like projections of syncy covering a core of cyto project into blood filled regions: primary villi: most form on the embryonic pole
  • 12 days
  • embryo now susceptible to infections
17
Q

membranes functions

A
  • mechanical protection and hydration: amnion
  • nutrition and vascularisation: yolk sac (umbilical cord + hemopoiesis + PGC)
  • waste disposal: allantois: ambilical cord ligament
  • delimitation and respiration: chorion: fetal part of placenta
18
Q

development of amnion

A
  • amniotic fluid (water/liquor amnii) protects embryo
  • 25 ml at 10wks to 400ml at 20wks
  • contains electrolytes, proteins, carbs, phospholipids, urea…
18
Q

trophoblast and the embryo at the end of w2

A
  • 2 germ layers
  • 2 cavities
  • 2 out of 3 embryo annexes: yolk sac, chorion (placenta) and yet to come the allantois
  • the amnion
  • the extra-embryonic cavity will be taken over by embryo and amnion
19
Q

yolk sac development

A
  • ultimately yolk sac is incorporated into umbilical cord
  • hosts primitive angiogenesis: primitive cardiovascular system
  • yolk sac mesenchyme cells - blood islands - central and peripheral cells
  • central to primitive blood cell - blood cell
  • peri to endothelial cell - vessels
  • endothelial tubes of intra and extraembryo are connected by connective body stalk
  • yolk sac hosts information of the PGC
20
Q

development of allantois

A
  • waste disposal
  • allantoid is initially a canal that drains the urinary bladder of fetus that runs within umbilical cord
  • contributes to the formation of umbilical cord vessels
  • provides ligaments and vessels to UC
  • support: postnatal remnant of allantois: converted to a fibrous structure: the umbilical ligament supporting the bladder
21
Q

early trophoblast (placental development)

A
  • uteroplacental circulatory system begins 11-13 days: cytotrophoblast cells proliferate budding into overlaying syncy:
  • formation of the primary chorionic stem villi occurs
  • extraembryonic mesoderm penetrates core transforming them to secondary chorionic stem villi
  • at end of W3 villous mesoderm forms blood vessels establishing uteroplacental circulaion
  • villi w blood vessels are tertiary
22
Q

tertiary villi

A
  • vessels greatly increase efficiency
  • mean diffusivity is higher in uterine wall than placenta: high levels of perfusion in maternal vessels
23
Q

amniochorionic membrane

A
  • at 12 weeks the chorion laeve (smooth chorion) fuses with the decidua parietalis compressed by the amnios and getting poorly vasculorised
  • expansion of amnion: fusion with smooth chorion: amniochorionic membrane: ruptures before birth
23
Q

cotyledons

A
  • The maternal cotyledons, or lobes, of the placenta are on the maternal side of the surface
  • Each cotyledon is a perfusion chamber partly or wholly separated from adjacent chambers by a wall of connective tissue, which may be lined by trophoblast cells
24
Q

cotyledon development

A
  • 4-5 months
  • decidual septa outgrow into intervillous spaces without reaching the chorionic plate
  • as a result placeneta is divided into compartments: cotyledons
25
Q

functions of the placenta

A
  • gas exchange
  • nutrient and electrolyte exchange
  • transmission of maternal antibodies
  • hormone production: progesterone, oestrogen, hCG, somatotropin
26
Q

placenta

A
  • made up by embryonic chorion frondosum (villous chorion) and maternal decidua basilis
  • maternal and fetal tissues form two closely bound units
  • chorionic plate consists of the amnion, extra-embryonic mesoderm, cytotrophoblast and syncytiotrophoblast
  • decidua basalis contains uterine vessels and glands
27
Q

cellular bases of placental barrier

A
  • barrier formed by the endothelium of fetal capillaries, connective tissue, trophoblasts
  • permeable to many viruses, bacteria and teratogens
28
Q

spontaneous twinning

A
  • monozygotic (3-4/1000)
  • dipolyzygotic (7-11/1000 increasing w maternal age
  • only 29% women pregnant w twins give birth
  • 10-20% die at birth
  • 12% premature infants are twins

embryology (9 decks)

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