GENERAL EMBRYOLOGY

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GENERAL EMBRYOLOGY

• 1. Development of embryology
• 2. Germ cell and fertilization
• 3. Blastocyst and implantation
• 4. Formation of the germ layer
• 5. Differentiation of trilaminar germ and
  formation of embryo
• 6. Fetal membrane and placenta
• 7. Twins and multiple birth

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• Preembryonic period 1st week to end of 2nd week
• fertilization to formation of bilaminar germ
  disc
• Embryonic period 3rd week to end of 8th week
• formation of embryo
• Fetal period 9th week to birth
• growth
• Perinatal stage 26th week to 4 week after birth

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• Animal

• Plant

Human ?
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Development of embryology

• Aristotle, B.C 384-322

Semenmenstration

• Harvey, 1651

All life from oocyte

• Malpighi, 1675

A micro-chicken in an egg

• Leewenhoek, 1677

A micro-human in a sperm
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• Haeckel, 1868
• Biogenetic law

• Spemann, 1869-1941
• Experimental embryology

• Wilmut,1997
• Dolly

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Germ cell and fertilization

• Germ cell
• spermatozoon and ovum
• 1. Spermatozoon
• CapacitationIn female reproductive tract, the
  sperms were enabled to bind to the zona pellucida
  receptors.
• removal of glycoproteins (decapacitation
  factor) which cover the sperms
• 2. Ovum
• secondary oocyte arrested at metaphase in
  the second meiotic division

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Fertilization The process in which the
spermatozoon penetrates
into the ovum to form fertilized ovum.
In the ampulla of
oviduct
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Process of fertilization
Sperm bind to sperm receptor ZP-3 induce Acrosome
reactionrelease of acrosomal enzyme
Cell membrane of ovum
Penetration and release of acrosomal enzyme
nucleus
acrosome
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ovum
fertilized ovum
sperm
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• Zona reaction Cortical granules?perivitelline
  space ?degrade ZP-3, alteration of zona pellucida
  ?barrier for sperm penetration

• The second meiotic division of the secondary
  oocyte is rapidly lifted and the second polar
  body is released, leaving a haploid female
  nucleus.

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Contac of sperm and ovum
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Sperm penetrate into the ovum
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Formation of female and male pronucleus
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Fusion of pronuclei
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Process of fertilization
? The nucleus of sperm penetrate
into ovum
? Formation of pronuclei
? Fusion of pronuclei
? Fusion of the membrane of
sperm and ovum
24 h
Alteration of ovum
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• 2.Condition of fertilization
• ? Normal ovum
• ? Normal sperm
• sufficient numbers
• ? Certain time
• 12-24h
• ? Free reproductive tract

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• 3.Significance of fertilization
• ? A new life
• ? Diploid
• inheritance and aberrance
• ? Sex determination

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Formation of blastocyst and implantation

• Cleavage and formation of blastocyst
• 1. Cleavage early division of fertilized egg
• 2. Blastomeredaughter cells from cleavage
• 3. Morula12 to 16- cell stage, enclosed in the
  zona pellucida,
• like morus
• 4. Blastocystabout 100 blastmeres
• blastocoele?inner
  cell mass and trophoblast
• polar
  trophoblast

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Phase of cleavage
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Morula
12 to 16-cell stage The third day
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Appearance and inner structure of blastocyst
Appearance
Inner structure
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Movement of fertilized egg in the oviduct
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• Implantation (imbed)
• The process by which the blastocyst
  settles
• into endometrium. 6th day to 11th day
• Fundus and body of uterus
• zona pellucida disappear at the 5th day
• 1.Trophoblastproliferate and differentiate into
  two layers
• ?Syncytiotrophoblastouter layer, fused each
  other, cell boundaries disappear
• ?Cytotrophoblastinner layer, cell boundaries
  distinct, simple cuboidal cells

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Movement and implantation of fertilized egg
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Implantation at 7th day
Cytotrophoblast
Inner cell mass
Polar trophoblast
Endometrium
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• 2.Decidua
• endometrium implantation decidua
• decidual response
• Decidua basalisunder the implantation site
• Decidua capsularisbetween the implantation
• site and the uterine lumen
• Decidua parietalisremaining endometrium

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Decidua
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Formation of germ layer

• Bilaminar germ disc
• 1.Bilaminar germ disk
• Inner cell mass?2 layers of cell in disc
  (7th day)
• Epiblast columnar cells adjacent to
  trophoblast
• Hypoblast cuboidal cells adjacent to
  blastocoele

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Epiblast
Columnar cells
Bilaminar germ disc
Hypoblast
Cuboidal cells
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• 2. Amnion8th day
• epiblast ? amnioblast ? aminiotic membrane ?
  amniotic cavity ? amniotic fluid
• 3.Primary yolk sac 9th day
• hypoblast ?extraembyronic endoderm ?primary
  yolk sac

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Bilaminar germ disc at 9th day
Primary yolk sac
Hypoblast
Epiblast
Amniotic cavity
Syncytio-trophoblast
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Bilaminar germ disc
Decidua
Syncytiotrophoblast
Cytotrophoblast
Amniotic cavity
Epiblast
Hypoblast
Primary yolk sac
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• 4. Extraembryonic mesoderm 10th-11th day
• 5. Extraembryonic cavity 12th-13th day
• Extraembryonic mesoderm visceral layer
• 
  parietal layer
• 6. Secondary yolk sac 13th day
• 7. Body stalk 14th day

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Embryo at 10th day
Primary yolk sac
Extraembryonic mesoderm
Germ disc
Amnion
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Bilaminar germ disc
Decidua
Amniotic cavity
Epiblast
Primary yolk sac
Hypoblast
Cytotrophoblast
Extraembryonic mesoderm
Syncytiotrophoblast
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Embryo at 13th day
Extraembryonic cavity
Primary yolk sac
Secondary yolk sac
Body stalk
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Bilaminar germ disc
Primary stem villus
Body stalk
Extraembryonic mesoderm Visceral layer
Secondary yolk sac
Extraembryonic cavity
Extraembryonic mesoderm Parietal layer
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Formation of trilaminar germ

• Trilaminar germ disc
• primitive streak, primitive groove 3rd
  week
• primitive node, primitive pit
  3rd week
• 1. Endoderm primitive groove ?hypoblast ?
  endoderm
• 2. Mesoderm primitive groove ?between epiblast
  and hypoblat ?mesoderm
• 3. Ectodermepiblast ?ectoderm

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Primitive streak
Epiblast
Hypoblast
Epiblast
Primitive streak
Hypoblast
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• Determine the
• direction of the
• embryo
• notochord

Significance of primitive streak
Primitive node
Primitive pit
Primitive groove
Primitive streak
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Formation of endoderm
Epiblast
Primitive streak
Endoderm
Hypoblast
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Formation of mesoderm
Epiblast

Mesoderm
Endoderm
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Trilaminar germ disc
Ectoderm
Mesoderm
Endoderm
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proliferation
Head process
Notochordal tube
Neurenteric canal
Notochord
Epiblast
Primitive pit
Significance of notochord ?
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No mesoderm
Buccopharyngeal membrane
Cloacal membrane
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Differentiation of trilaminar germ and formation
of embryo

• Differentiation of trilaminar germ
• 1.Differentiation of ectoderm
• ?Neural tubeblastema of CNS
• neural plate (18th-19th day)
• Neuro-epithelium (neural ectoderm)
  pseudostratified columnar
• ?neural groove , neural fold
• ? neural tube (closed at 22nd
  day)

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Neural groove
Paraxial mesoderm Intermediate
mesoderm
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Neural groove Paraxial
mesoderm intermediate mesoderm
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Neural groove
Neural crest
Notocord
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1?Differentiation of ectoderm
Anterior neuropore closed at 25th
Neural fold
Neural tube
closed at 22nd day, from 4th somite
Posterior neuropore closed at 27th
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Unclosed Anterior neuropore
Unclosed Posterior neuropore
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• ?Neural crest blastema of PNS
• chromaffin cell,
  parafollicular cell
• some of bone,
  cartilage and
• muscle of head
• ?Superficial ectoderm after formation of neural
  tube
• epidermis

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• 2.Differentiation of mesoderm 17th day
• ?Paraxial mesodermsomite at 20th day, from
  the head
• Dermotome?
  dermis, hypodermis
• Myotome
  ? skeletal muscle,
• 
  Sclerotome ? axial skeleton.
• ?Intermediate mesodermurinary and
  
• 
  reproductive system
• ?Lateral mesodermparietal mesoderm,
• viseral
  mesoderm,
• 
  intraembryonic coelomic cavity

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Somite
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Differentiation of lateral mesoderm
Dermatome
Sclerotome
Parietal mesoderm
Intraembryonic coelomic cavit
Visceral mesoderm
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Differentiation of lateral mesoderm
Intraembryonic coelomic cavity
Extraembryonic coelomic cavity
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• 3. Differentiation of endoderm
• Epithelium of primitive gut ?
• epithelium of digestive tract, digestive
  gland,
• respiratory tract and lung
• Primitive pharynx ?5 pairs of pharyngeal pouch

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Formation of primitive gut
A
B
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Parietal mesoderm
Intraembryonic coelomic cavity
Visceral mesoderm
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• Formation of embryonic body (4-8th week)

20-30th day
Disc
Column
folds
the number of somite increase face
development, formation of branchial pouch
breach of buccopharyngeal membrane 5th week
upper and lower limb buds 6th week hand and foot
plates 7th week formation of face, disappear
of somite 8th week breach of cloacal membrane
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At the end of 8th week
a small human
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Fetal membrane and placenta

• Fetal membrane
• Chorion
• Amnion
• Yolk sac
• Allantois
• Umbilical cord

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Amnion
Yolk sac
Umbilical cord
Placenta
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• 1.Chorion
• Secondary stem villus chorinic plate
• Primary stem villus2nd week
• Outer
  syncytiotrophoblast
• Inner
  cytotrophoblast
• Chorinic plate extraembryonic mesoderm
• trophoblast

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• Secondary stem villus3rd week
• Outer syncytiotrophoblast
• Intermedial extraembryonic
  mesoderm
• Inner cytotrophoblast
• Tertiary stem villusend of 3rd week, Blood
  vessels
• Anchoring villus, Free villus
• cytotrophoblastic cell column ?
• cytotrophoblastic shell

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Primary stem villusat 2nd week,cytotrophoblast
Secondary stem villusat 3rd
week,extraembryonic mesoderm
Tertiary stem villusat the end of 3rd
week,blood vessels
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Stem villus

Free villus
Anchoring villus
Cytotrophoblastic column
Cytotrophoblastic shell
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• Evolvement of chorion

Chorion laeveadjacent to decidua
capsularis Chorion frondosum adjacent to decidua
basalis
6th weeks
Chorion laeve
Chorion frondosum
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• Abnormility of chorion

• Hydatidiform

Picture

• Chorion carcinoma

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Hydatidiform
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Hydatidiform
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Hydatidiform
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Chorion carcinoma
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Chorion carcinoma
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Chorion carcinoma
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• 2. Yolk sac5th-6th week, atresia
• Abnormality
• ? Meckels diverticulum
• ? Umbilical fistula
• ? Primitive blood cells
• ? Primordial germ cells

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• 3. Amnion
• amniotic membrane 0.2-0.5mm
• amniotic epithelium extraembryonic
  mesoderm
• amniotic fluid 500-1000ml
• abnormality lt500 ml, oligohydramnios
• gt2000 ml,
  polyhydramnios
• protection

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• 4. Allantoisdegeneration
• Abnormality
• Urachal fistula
• 2 pairs of blood vessel?
• 1 umbilical vein
• 1 pair of umbilical
  artery

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• 5. Umbilical cord50 cm
• (CT, umbilical vein, umbilical artery,
• degenerated yolk sac and allantois)
• covered with amniotic membrane
• Abnormality gt80 cm,
• lt35 cm
• connect fetus with
  placenta

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Fetal membrane
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• Placenta
• 1.Placenta Chorion frondosum Decidua basalis
• disk 15-20cm
• Sandwich chorinic plate (fetus)
• villi
• basal plate (mother)
• basal plate decidua
  cytotrophoblastic shell
• placental septa ? cotyledon (incomplete)

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Umbilical artery
Umbilical vein
Decidua bsalis
Placenta septa
Spiral artery
Uterus vein
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• 2.Placental membrane
• Structure between the blood of mother and
  fetus
• ?Syncytiotrophoblast
• ?Cytotrophoblast and its basal lamina
• ?Connective tissue
• ?Endothelium and its basal lamina
• protection

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Fetal membrane
Syncytiotrophoblast
Cytotrophoblast
???
Basal lamina
Blood of mother
Connective tissue
Basal lamina
Endothelium
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• 3.Function
• ? Substance exchange
• O2, nutriment, CO2, waste
• ? Hormone
• Human chorionic gonadotropin, HCG
• Human placental lactogen, HPL
• Human placental progesterone, HPP,
• Human placental estrogen, HPE

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Placenta
Function

• ? Substance exchange

Capillary of fetus Blood of mother
O2
Nutriment
water?salt?others water?salt?others
CO2
Metabolic waste
Placenta membrane
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Placenta
Function

• ? Barrier

Capillary of fetus Blood of mother
s




Most of microorganism
No way!
Placenta barrier
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Placenta
Function

• ? Barrier

Capillary of fetus Blood of mother
Most of drugs




Most of microorganism
Some of microorganism
Placenta barrier
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Placenta
Function

• ? Endocrine

Hormone Function Appearance Fastigium
HCG Corpus luteum Pregnancy 3rd week 8th week
HCS Mammary gland 2nd month 8th month
HPE Corpus luteum 4th month 8th month
HPP Corpus luteum 4th month 8th month
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• Twins and multiple birth
• 1.Twins
• monozygotic twins
• dizygotic twins

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• 2.Multiple birth
• monozygotic multiple birth
• polyzygotic multiple birth
• mixed multiple birth

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• Dizygotic twins

Blastocyst Blastocyst 2 Amnion
2 Amnion 2 Chorion 2
Chorion 2 Placenta 2 Placenta
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• Monozygotic twins
• 
  separation of blastomere, of ICM,
  of primitive streak
• 
  
• Blastocyst 2 ICM
  2 primitive streak
• 2 Amnion 2 Amnion
  1 Amnion
• 2 Chorion 1 Chorion
  1 Chorion
• 2 Placenta 1 Placenta
  1 Placenta