Download Blastogenesis

Blastogenesis
DCT 144
Cleavage
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Zygote
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Blastomeres
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Morula
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Blastocyst
Cleavage
Cleavage – mitotic division without cell growth and
without proteosynthesis
Doughter cells (blastomeres) become smaller and embryo
does not change its size, being surrounded by zona
pellucida
Mitotic division is total and equal
Formation of 2 cells (24 hours)
4 cells (40 hours)
6 – 12 cells (3ED)
16 – 32 cells (4ED) . This stage is called morula
Differentiation blastomeres
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Blastomeres start to differentiate on the stage
consisting 8 cells – expression of adhesive proteins
– association and polarization of cells
Tight and gap junction – outer cell mass trophoblast
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Cells in centre – inner cell mass – embryoblast
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Cavity in blastocyst comprises fluid
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Blastocyst – Embryonic pole
Vegetative pole
Blastocyst
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Trophoblast – outer cell mass
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Embryoblast – inner cell mass
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Blastocyst cavity
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– from ED 4
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) Imprinted genes, that are active from
father, cause chorion development
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
Prenatal losses
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Implantation tests embryos
Chromosomal abnormalities are the
most frequent causes of spontaneous
abortion
Immune reason - auto-antibodies
More that 50% embryos are unable to
implant
Only 25 – 30% zygotes survive to birth
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
Development of embryoblast
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Inner cell mass
differentiates in
two layers even
before
implantation epiblast and
hypoblast
Epiblast – columnar
cells
Hypoblast – cubic
cells
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)
−
Production of serum proteins, metabolism of
nutrients
−
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)
Placenta
Fetal organ providing nutrition and other
function to embryo:
Functions:
Metabolism (synthesis – glycogen)
Transport of gases and nutrients
Excretion of vaste products
Hormone production (hCG)
Structure
Fetal part – chorion
Chorionic plate
Chorionic villi
Maternal part
Endometrium – part
functionalisdecidua basalis
Structure
Placental shape – discoid (olliformis) +
haemochorial
Placental septa – rests of decidua basalis.
They separate placenta from maternal
side in lobes - cotyledons
Cotyledons – contain 2 and more anchoring
villi
Diameter – 15 -20 cm, thickness 2-3 cm,
weight 500 to 600 g
Placental villus
Function of trophoblast
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Transport of respiratory gases
Transport of metabolites and
electrolytes
Transport of maternal antibodies (IgG)
Production of hormones: progesteron,
estriol, hCG, somatomammotropin
(placental lactogen)
Placental transport
Difusion
Facilitated difusion
Active transport
Pinocytosis
Other types of transfer:
Damage of placetal barrier – blood cellas
Own activity – Treponema pallidum
Damage due to infection - toxoplasmosa
Transport
Many substances from maternal blood may
transfer placental barrier including drugs
Nutrients – glucose, AK, fatty acids, water,
vitamines, electrolytes
Hormones – only steroid unconjugates
Maternal antibodies, transferin+ iron
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
Twins
Dizygotic versus monozygotic
Dichorial x monochorial
Diamniotic x monoamniotic
Conjointed twins