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I n d r i a t i D w i R
Department of Anatomy-Histology
Faculty of Medicine
Brawijaya University
– Production of egg and sperm
gametogenesis
– Transport gametes and fertilization
– Cleavage
– Embryo transport and implantation
– Formation of germ layers
– Establishment of the Basic Embryonic Body Plan
Embryonic stage (2 to 2)
1st week development
Counting the days…
• Day by day of the conceptus
Week 2, days 8 – 14
Week 3 -8 [embryonic periode]
Month 3 to birth [fetus] : OOT
• The Placenta and Fetal Membranes
Implantation of the
blastocyst is completed
during the second week
• Day by day of the conceptus
Week 2, days 8 – 14
Week 3 -8 [embryonic periode]
Month 3 to birth [fetus] : OOT
• The Placenta and Fetal Membranes
• Day by day of the conceptus
Week 2, days 8 – 14 Week 3 -8 [embryonic periode]
Month 3 to birth [fetus] : OOT
• Day 8
– The blastocyst embeded partially in endometrium
– Trophoblast has differentiated into 2 layer :
• Inner layer of mononucleated cellCytotrophoblast
• Outer layer of multinucl Syncytiotrophoblast
– Embryoblast also differentiated into 2 layer :
• An upper layer of cuboidal cells epiblast
• A lower layer of collumnar cells hypoblast
• Day 9
– The blastocyst more deeply embeded
– Penetration defect closed by fibrin
coagulum
– Appear vacuole at syncytiotroph fuse
lacunae
– extraembryonic endoderm→exocoelomic
membrane → primary yolk sac
(exocoelomic cavity)
Formation of Bilaminar GermDisc
• Day 11 and 12
– decidual response of endometrium /stroma cell→
predecidual cell→ decidual cell(cell become larger
and rich in glycogen and lipid droplet)
• Day 13
– The hypoblast produce cells that migrate along the
inside of exocoelomic cavity secondary yolk sac,
large portion exocoelomic cyst
– Extraembryonic cavity expand chorionic cavity
– Conecting stalk : formed by extraembryonic
mesoderm
– the primitive streak appears for the first time
Formation of Bilaminar Germ Disc
• Choriocarcinoma :
mallignant tumor derived from embryonic
cytotrophoblast and syncytiotrophoblast.
– Highly invasive into maternal deciduas
– Contain only paternal chromosome parental
imprinting
Clinical corellation
Clinical corellation
Day by day of the conceptus
Week 2, days 8 – 14
Week 3 -8 [embryonic periode]
Formation of Germ Layers and Early Tissue and Organ Differentiation: Third Week
Organogenetic Period: Fourth to Eighth Weeks
Month 3 to birth [fetus] : OOT
• = Early Tissue and Organ Differentiation
• Trophoblast cells continue to invade uterine wall in the process of early placentation. Primary villi 2nd
dst
• Within the conceptus, gastrulation converts the bilaminar embryo into the trilaminar embryo
• Formation of notochord
Third Week
Trilaminar germ disc= endoderm + mesoderm
+ ectodermdetermination of head and tail
of germ disc
• endoderm: hypoblast cells are replaced by
epiblast cells
• ectoderm: epiblast changed the name into
ectoderm
• mesoderm: intraembryonic mesoderm
Formation of Trilaminar Germ Disc
[ Third week of development]
Formation of mesoderm: early of 3 weeks Gastrulation :
– primitive streak: cells of epiblast proliferate to form a
longitudinal arranged cell cord
– primitive groove
– primitive node
– primitive pit
• Head process (The notochordal process gives an
appearance of being a prolongation of the primitive
streak in the direction of the future head region of the
embryo) →notochordal tube → notochord :
– buccopharyngeal membrane
– cloacal membrane
Formation of Trilaminar Germ Disc
• The notochordal process immdiately rostral to the primitive
node and streak
• blood islands of the umbilical vesicle
• Teratogenesis associated with gastrulation :
– Holoprosencephaly :
• High dose alcohol kill cells in the anterior midline of germ disk deficiency of the craniofacial structures
– Sirenomelia (caudal dysgenesis)
• Genetic abN/toxicdisrupted gastrulation insufficient mesoderm at caudal region
– Situs inversus (transposition of viscera at thorax and abdominal cavity)
– Saccococcygeal teratomas :
• Remnant of primitive streak persist in sacrococcygeal region
• Also arise from PGCs
Clinical corellation
Clinical corellation
Female infant with a large
sacrococcygeal teratoma that
developed from remnants of the
primitive streak
Clinical corellation
Differentiation of trilaminar germ disc: 4th –
8th weeks
• differentiation: same cells which are
primordial and immature differentiate into
different cells which have specific structure
and function
• induction: some tissues effect the
differentiation, and determine the
differentiating orientation of another tissue
Fourth to eight week
4 to 8 week of development (organogenesis)
• Differentiation of ectoderm: CNS
• Differentiation of mesoderm: dermis, bone, cartilage, CT, muscles, pleura, peritoneum and pericardium, cardiovascular and lymph system
• Differentiation of endoderm: digestive, respiratory and urinary system
Differentiation of ectoderm: from 18th –19th days
• neural plate: neuro-epithelium(neural ectoderm):
pseudostratified columnar epithel.
• neural fold
• neural groove
• neural tube: →CNS
/anterior neuropore: closed by 25th days
/posterior neuropore: closed by 27th days
• neural crest(mesoectoderm): two lines of cell
cords→ganglion
organogenesis
• Anencephaly:
anterior nurophore
fail to elevate fuse
• Meningocele :defect
of neural tube
Clinical corellation
embryonic
Differentiation of mesoderm: 17th days
• paraxial mesoderm
– somite: 20th days, 3 pairs/per day, 42-44 pairs by the
end of 5th weeks
– sclerotome: →bone, cartilage
– myotome: →skeletal muscle
– dermatome: dermis and hypodermis
• Intermediate mesoderm:→kidney and
reproductive gland
– nephrotome: segmentation
– nephrogenic cord:
organogenesis
• lateral mesoderm:
– intraembryonic coelom: →body cavity
– somatic or parietal mesoderm: →muscle, CT,
parietal layer of pleura, peritoneum and
pericardium
– splanchnic or visceral mesoderm: →muscle, CT
of digestive tract, visceral layer of pleura,
peritoneum and pericardium
– mesenchyme: →cardiovascular and lymph
system
organogenesis
Differentiation of endoderm:
• primitive gut: →digestive, respiratory and
urinary system
organogenesis
• Day by day of the conceptus
Week 2, days 8 – 14
Week 3 -8 [embryonic periode]
Month 3 to birth [fetus] : OOT
Third month to birth :
• Fetal period
• Its characterized by maturation of tissues and rapid growth of the body
• Monthly changes :
– Third month : face more like human, primary ossification, intestine withdraw into abdominal cavity
– Fourth to fifth week : the fetus lengthens rapidly, movement of the fetus can be felt by the mother
• Sixth month :
– 50% full term weight is added
– The respiratory system and CNS have not
differentiated sufficiently
• Seventh to ninth month :
– Deposition of subcutananeous fat
– At the end of ninth month : the skull has largest
circumference, weight normal fetus 3000-3400g
– Sexual characteristics are pronounced
Fetal period
Time of birth
• The length of pregnancy is considered to be 280 days or 40 weeks after the onset of last normal menstrual period or more accurately 266 days or 38 weeks after fertilization
• If they are born much earlier : premature; if born later : postmature
• The age of embryo or small fetus determined by combining data of the onset last menstrual period with fetal length, weight, and morphological characteristic
• Valuable tool for assisting determination is ultrasound CRL and biparietal diameter
• Low birth defect :
– 1 in 10 babies has IUGR
– Fetally malnourished or dysmature
– Increased risk of neurogical deficiencies, congenital
malformation, meconeum aspiration, hypoglycemia,
hypocalcemia, RDS.
– Fetuses that weight less than 500 g seldom survive,
500-1000 g survive with expert care
Clinical corellation
• Day by day of the conceptus
Week 2, days 8 – 14
Week 3 -8 [embryonic periode]
Month 3 to birth [fetus] : OOT
• The Placenta and Fetal Membranes
The Decidua three regions of the decidua are named according to their relation
to the implantation site :
• The decidua basalis is the part of the decidua deep to the
conceptus that forms the maternal part of the placenta.
• The decidua capsularis is the superficial part of the decidua
overlying the conceptus.
• The decidua parietalis is all the remaining parts of the
decidua.
components:
• The fetal part : formed by the villous chorion.
The chorionic villi that arise from it project into the
intervillous space containing maternal blood.
• The maternal part : formed by the decidua basalis
By the end of the fourth month, the decidua basalis is almost
entirely replaced by the fetal part of the placenta.
The placenta and fetal membranes perform the following
functions and activities: protection, nutrition, respiration,
excretion, and hormone production
The Placenta
Development of the Placenta
• Early placental development is characterized by the rapid
proliferation of the trophoblast and development of the
chorionic sac and chorionic villi
• A complex vascular network is established in the placenta
by the end of the fourth week, which facilitates maternal-
embryonic exchanges of gases, nutrients, and metabolic
waste products.
• The formation of the placenta requires a precise
developmental progression of the trophoblast cells.
• Trophoblast cells, generate most of the placental
structures.
• Proliferation of these trophoblast cells produces a two-
layered wall consisting of an inner cytotrophoblast layer
and an outer syncytiotrophoblast layer.
• The syncytiotrophoblast will eventually become the only
cellular layer separating the fetal capillaries within the
placental villi from the maternal blood.