Download Embryology II 2008 Cleavage Zygote Blastomeres Morula Blastocyst

Embryology II
2008
Cleavage
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Zygote
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Blastomeres
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Morula
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Blastocyst
Blastocyst
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Trophoblast – outer cell mass
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Embryoblast – inner cell mass
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Blastocyst cavity – from ED 4
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ED5 - loss of zona pellucida – “hatching” possibility of implantation
Cells of trophoblast express adhesive molecules –
adhesion to the epithelial lining of uterus
(secretory phase of menstrual cycle)
Implantation
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Adhesion to the endometrium – embryonic pole
Trophoblast – proliferation and cell coalescence –
syncytium
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Cytotrophoblast – proliferating cells
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Syncytiotrophoblast – loss of inter-cellular borders
Implantation – proteolytic enzymes
(metalloproteinases) – cytotrophoblast
Syncytiotrophoblast – penetrates among epithelial
cells = it pull embryo in the endometrium
Implantation
Implantation
Implantation
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ED 9 – blastocyst is implanted in mucosa
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It is covered by the coagulation plug
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Syncytiotrophoblast develops in contact places
with maternal tissue, successively surrounds
whole blastocyst
Maternal reaction on embryo – decidual reaction
– secretion of mucus, glycogen accumulation
and oedema
Decidua basalis, marginalis, capsularis and
parietalis
Immune reaction
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Endometrium – immunologically favored tissue
Progesterone – decreases nonspecific immune reaction –
(complement)
Secretion of Interleukin-2 – decreases specific reaction
Syncytiotrophoblast and cytotrophoblast does not
express common antigens – or they are covered - both
form barrier between maternal and fetal tissues
Cytotrophoblast shell – cells of cytotrophoblast penetrate
stem villi and form barrier between maternal and fetal
connective tissues
Ectopic implantation
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Abdominal cavity (Douglas pouch – retro-uterine
cavity), ovary (primary ovarian pregnancy),
uterine tube (95%) - most frequent in ampulla,
intestitiale – in uterine horn
Placenta previa
Placenta accreta, percreta – penetrates into the
zona basalis and myometrium
Prenatal losses
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Implantation tests embryos
Chromosomal abnormalities are the most frequent
causes of spontaneous abortion
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Immune reason - auto-antibodies
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More that 50% embryos are unable to implant
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Only 25 – 30% zygotes survive to birth
Development of embryoblast
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Inner cell mass differentiates in two layers even
before implantation - epiblast and hypoblast
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Epiblast – columnar cells
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Hypoblast – cubic cells
Amnion
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Amniotic cavity (ED8)
– appears among cells
of epiblast –
differentiation into
amnioblasts and
columnar cells of
epiblast
Cavity is small, later
surrounds whole
embryo
Hypoblast
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Cell proliferation and migration along the
cytotrophoblast - (squamous epithelium) lining
of blastocyst cavity – exocoelomic Heuser´s
membrane
Blastocyst cavity is also called exocoelomic
cavity or primary yolk sac
Extraembryonic reticulum (extracellular matrix)
is produced between Heuser´s membrane and
cytotrophoblast
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ED12 – cells – extraembryonic mesoderm
(probably from epiblast)
Exocoelomic vesicles – they fuse in new
chorionic cavity – extraembryonic coelom –
between yolk sac and cytotrophoblast
Cavity growth separates amnion and yolk sac
from chorion – junction – connecting stalk
Mesoderm – visceral and parietal layers
Yolk sac
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ED12 - hypoblast proliferates again – cells
migrate along Heuser´s membrane – secondary
definitive yolk sac (smaller than primary)
Primary yolk sac – exocoelomic vesicules disappears
Function
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Haematopoesis and development of vessels –
vitellinne vasculature (blood islands)
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Production of serum proteins, metabolism of
nutrients
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Germ cells
Embryonic nutrition
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Resource in embryo – for first 4 – 8 blastomers,
only
Nutrition – diffusion from fluid in uterine tube
and uterus
Growth (proliferation) needs effective transport of
gases (oxygen and carbon dioxide) and
metabolites into the cells – development of
vessels and placenta
Development of chorionic villi, cardiovascular
system, contact with maternal blood
Development of chorion - placenta
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Development of lacunae in trophoblast (ED9)
Contact with maternal vessels – blood into the
lacunae – intervillous spaces
Vascular system needs adaptation for pregnancy –
development of utero-placental vessels from
spirale arteries (under influence of hormones) –
otherwise IUGR develops
Implantation is regulated by hormones – takes
place in the lamina functionalis, only
Development of chorion
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Chorion frondosum, chorion laeve
Primary stem villi – syncytiotrophoblast and
cytotrophoblast (ED 11 to 13)
Secondary stem villi – syncytiotrophoblast,
cytotrophoblast, extraembryonic mesoderm
(ED16)
Terciary stem villi (definitive) –
syncytiotrophoblast, cytotrophoblast,
extraembryonic mesoderm and vessels (ED21)
Function of trophoblast
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Transport of respiratory gases
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Transport of metabolites and electrolytes
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Transport of maternal antibodies (IgG)
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Production of hormones: progesteron, estriol,
hCG, somatomammotropin (placental lactogen)
Development of embryoblast gastrulation
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Development of 3 germ layers: ectoderm,
mesoderm and endoderm
Proliferation – formation of primitive knot and
primitive streak
Loos of
intercellular
junctions
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Bottle cells
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Cell migration
Formation of embryonic axis
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Antero-posterior
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Embryonic – vegetative pole
Embryonic axes
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Antero-posterior
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Left-right
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Dorso-ventral
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Cells are determinated
for different structures
of the body
Fate map
Basic morphogenetic processes
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Proliferation
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Apoptosis
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Association – cells express intercellular junctions
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Migration – loss of intercellular contacts – cells
express adhesive molecules for attachment to the
intercellular matrix
Induction → determination and differenciation
Regulatory genes
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Transcription factors – specific – in certain types
of cells or stages of development (promoter or
enhancer) genes beginning developmental
cascade or network – signal transduction pathway
- basic helix-loop-helix or zinc finger
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Signaling molecules – growth factors
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Receptors for signaling molecules are also needed
Cascade of regulatory genes
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Maternal effect
genes – anteroposterior axis, germ
cells
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Zygotic:
Segmentation genes
– gap, pair-rule,
segment-polarity
genes
Homeotic (Hox)
Homeodomain proteins
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Hox genes – in clusters
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Cranio-caudal segmentation of the body

Genes are activated and expressed according to a
strictly sequence
Pax genes – development of CNS, senses and
epithelial cells
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Sox genes
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Other – Lim
Signaling molecules –
cytokines, growth factors
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TGF-β, FGF, BMP4
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Hedgehog, Wnt (wingless)
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Chordin, noggin, follistatin,
activin, lefty
Cell surface receptors
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Receptor kinases (tyrozin, serin-threonin)
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Notch – lateral inhibition - prevent cells from
differentiation into the same cell type - neurons
Signaling molecules
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Retinoid acid (vitamine A) binding to CRABP
(cellular retinol-binding protein) – transcription
factor
Function – regulation of hox genes, cell
differenciation (epithelial cells, blood cells)
Vitamine A is strong teratogene.