Department of Anatomy-Histology Brawijaya...

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


Week 2, days 8 – 14 Week 3 -8 [embryonic periode]


• 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

Day by day of the conceptus



Formation of Germ Layers and Early Tissue and Organ Differentiation: Third Week

Organogenetic Period: Fourth to Eighth Weeks


• = 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



Female infant with a large

sacrococcygeal teratoma that

developed from remnants of the

primitive streak

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


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

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


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.

Department of Anatomy-Histology Brawijaya...

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