embryology nandini
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EMBRYOLOGY
Power point presentation by
Dr. Nandini Dhargalkar
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Embryology
Embryology study of the origin
and development of single
individual
Prenatal period
Embryonic period first 8 weeks
Fetal period remaining 30 weeks
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Fetal Period
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The Basic Body Plan
Skin dermis and epidermis
Outer body wall trunk muscles, ribs,
vertebrae Body cavity and digestive tube (inner
tube)
Kidneys and gonads deep to body wall
Limbs
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The Basic Body Plan
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The Embryonic Period
Week 1 from zygote to blastocyst
Conception in lateral third of uterine tube
Zygote (fertilized oocyte) moves toward the
uterus
Blastomeres daughter cells formed fromzygote
Morulasolid cluster of 1216 blastomeres Mulberry
Blastocyst fluid-filled structure ~ 60 cells
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The Embryonic Period
Stages of first week Zygote
4-cellMorula
Early blastocyst
Late blastocyst (implants at thisstage)
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Fertilization and the Events of the
First 6 Days of Development
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General development
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Stage 1
Facts: Week 1,
size 0.1-0.15 mm
Features: zygote,
fertilized oocyte,
pronuclei, polar
bodies, zonapellucida
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Stage 2
Facts: Week 1, 2-3 days, size 0.1-
0.2 mm
Features: zona pellucida,
blastomeres
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Stage 3
Facts: Week 1, 4 -
5 days, size 0.1-0.2
mmFeatures: zona
pellucida,
trophoblast shell,inner cell mass,
blastoceol
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Stage 4
Facts: Week 1, size 0.1-0.2
mm
Features: adplantation and
implantation commences,increase in hCG
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Stage 5
Facts: Week 1, size 0.1-0.2 mm
Features: implantation
completed, inner cell mass,
bilaminar embryo, trophoblast
development
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Week 2 The Two-Layered Embryo
Bilaminar embryonic disc inner cell mass divided into twosheets Epiblast and the hypoblast
Together they make up the bilaminar embryonic disc
Amniotic sac formed by an extension of epiblast Outer membrane forms the amnion Inner membrane forms the amniotic sac cavity
Filled with amniotic fluid
Yolk sac formed by an extension of hypoblast
Digestive tube forms from yolk sac NOT a major source of nutrients for embryo
Tissues aroundyolk sac Gives rise to earliest blood cells and blood vessels
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Implantation of the Blastocyst
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Implantation of the Blastocyst
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Implantation of the Blastocyst
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Stage 6
Facts
Human embryonic stage 6 occurs towards the end of week2 at approximately 13-14 days.
The embryo is now 0.2 mm diameter in size.
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Week 3 The Three-Layered Embryo
Primitive streak raised groove on the dorsal surface ofthe epiblast
Gastrulation a process of invagination of epiblast cells Begins at the primitive streak
Forms the three primary germ layers Three Germ Layers*
Endoderm formed from migrating cells that replace thehypoblast
Mesoderm formed between epiblast and endoderm
Ectoderm formed from epiblast cells that stay on dorsalsurface
*All layers derive from epiblast cells!
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The Primitive Streak
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The Primitive Streak
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Stage 7
View: embryonic disc, showing the epiblast
viewed from the amniotic (dorsal) side. Head
to tail orientation is Cranial (image top) and
Caudal (image bottom).
Features: embryonic disc, primitive node,
primative streak, primative groove, connecting
stalk Alternate View: embryonic disc, probably
from from the ventral side. Showing the
connecting stalk to the left.
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The Notochord
Primitive node a swelling at one end of
primitive streak
Notochord forms from primitive node and
endoderm
Notochord defines body axis
Is the site of the future vertebral column
Appears on day 16
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Formation of the Mesoderm and
Notochord
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Formation of the Mesoderm and
Notochord
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Neurulation
Neurulation ectoderm starts forming brain and spinalcord Neural plate ectoderm in the dorsal midline thickens
Neural groove ectoderm folds inward
Neural tube a hollow tube pinches off into the body Cranialpart of the neural tube becomes the brain
Maternal folic acid deficiency causes neural tube defects
Neural crest Cells originate from ectodermal cells
Forms sensory nerve cells Induction
Ability of one group of cells to influence developmentaldirection of other cells
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The Mesoderm Begins to Differentiate
Somites our first body segments
Paraxial mesoderm
Intermediate mesoderm begins as a
continuous strip of tissue just lateral to theparaxial mesoderm
Lateral plate most lateral part of the mesoderm
Coelom becomes serous body cavities Somatic mesoderm apposed to the ectoderm
Splanchnic mesoderm apposed to the endoderm
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Stage 8Facts
Human embryonic stage 8 occurs during week 3 between 17 to 19days.
The embryo is now 1.0 - 1.5 mm in size.
Events
Gastrulation is continuing as cells migrate from the epiblast,
continuing to form mesoderm.
Mesoderm lies between the ectoderm and endoderm as acontinuous sheet except at the buccopharyngeal and cloacal
membranes. These membranes have ectoderm and endoderm only
and will lie at the rostral (head) and caudal (tail) of the
gastrointestinal tract.
From the primitive node a tube extends under the ectoderm in the
opposite direction to the primitive streak. This tube forms first the
axial process then notochordal process, then finally the notochord.
The notochord is a key to embryonic folding and regulation of
ectoderm and mesoderm differentiation. It lies in the rostrocordal
axis and the embryonic disc will fold either side ventrally, pinching
off a portion of the yolk sac to form the lining of the
gastrointestinal tract.
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Changes in the Embryo
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Changes in the Embryo
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Stage 9
FactsHuman embryonic stage 9 occurs during week
3 between 19 to 21 days.
The embryo is now 1.5 to 2.5 mm in size and
somites have begun to form and number
between 1 to 3 somite pairs during this stage.
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Stage 9 contd
Events
Ectoderm - Neural plate brain region continues to expand, neural plate begins
folding over the notochord. Gastrulation continues through the primitive
streak region.
Mesoderm - Paraxial mesoderm segmentation into somites begins (1 - 3
somite pairs). Lateral plate mesoderm begins to vacuolate, dividing it into
somatic and splanchnic mesoderm and to later form the intra-embryonic
coelom. Prechordal splanchnic mesoderm begins to form the cardiogenic
region, from which the primordial heart will develop.
Endoderm - Notochordal plate still visible which will form the notochord.
Endoderm is still widely open to the yolk sac and germ cells form part of
this layer. Extra-embryonic mesoderm on the yolk sac surface begins to
form "blood islands".
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Week 4 The Body Takes Shape
Folding of embryo laterally and at the head
and tail
Embryonic disc bulges; growing faster than yolk
sac
Tadpole shape by day 24 after conception
Primitive gut encloses tubular part of the yolk
sac Site of future digestive tube and respiratory structures
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Week 4 The Body Takes Shape
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Stage 10Facts
Week 4, 22 - 23 days, 2 - 3.5 mm, Somite
number 4 - 12
Features
Somite Number 4 - 12, rostral neuropore,
neural folds in region of developing brain,
neural tube, somites, caudal neuropore, neural
fold fuses, remnant of amniotic sac
Events
Ectoderm: Neural fold deeepens, edges
approach midline, neural fold fuses, neural
plate folds ventrally in brain region
Mesoderm: Somitogenesis, continuedsegmentation of paraxial mesoderm (4 - 12
somite pairs)
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Stage 11
FactsWeek 4, 23 - 26 days, 2.5 - 4.5 mm, Somite Number 13 - 20
Events
Ectoderm: Neural tube continues to close, Rostral neuropore
closes
Mesoderm: continued segmentation of paraxial mesoderm (13 -
20 somite pairs), heart tube bending
Features
rostral neuropore closing, forebrain, neural tube in region of
developing spinal cord, somites, caudal neuropore, connecting
stalk, amnionIdentify: heart, rostral (cranial, anterior) neuropore closing,
forebrain, neural tube in region of developing spinal cord,
somites, caudal neuropore, connecting stalk, amnion
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Stage 12Facts
Week 4, 26 - 30 days, 3 - 5 mm, Somite Number 21 - 29Events
Ectoderm: Neural tube continues to close, Caudal
neuropore closes, forebrain
Mesoderm: continued segmentation of paraxial mesoderm
(21 - 29 somite pairs), heart prominence
Head: 1st, 2nd and 3rd pharyngeal arch, forebrain, site oflens placode, site of otic placode, stomodeum
Body:
heart, liver, umbilical, early upper limb bulge
Features
Features: day 26, 27 somites, forebrain, site of lens
placode, site of otic placode , stomodeum, 1st pharyngeal
arch, 2nd pharyngeal arch, 3rdpharyngeal arch, heart
prominence, somite
Identify: forebrain, site of lens placode, site of otic placode,
stomodeum, 1st pharyngeal arch, 2nd pharyngeal arch, 3rd
pharyngeal arch, heart prominence, somite
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Week 4 The Body Takes Shape
Derivatives of the germ layers
Ectoderm forms
Brain, spinal cord, and epidermis
Endoderm forms
Inner epithelial lining of the gut tube
Respiratory tubes, digestive organs, and urinary bladder
Notochord gives rise to nucleus pulposus within intervertebral discs
Mesoderm forms
Muscle
Bone Dermis
Connective tissues (all)
Mesoderm differentiates further and is more complex than the other two
layers
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Week 4 The Body Takes Shape
Mesoderm (continued) Somites divides into
Sclerotome
Dermatome
Myotome
Intermediate mesoderm forms Kidneys and gonads
Mesoderm (continued) Splanchnic mesoderm
Forms musculature, connective tissues, and serosa of the digestive andrespiratory structures
Forms heart and most blood vessels
Somatic mesoderm forms Dermis of skin Bones Ligaments
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Derivatives of Germ Layers
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Stage 13
FactsWeek 4-5, 26 - 30 days, 3 - 5 mm, Somite
Number 21 - 29
Events
Ectoderm: Neural tube continues to close,
Caudal neuropore closes, forebrainMesoderm: continued segmentation of
paraxial mesoderm (21 - 29 somite pairs),
heart prominence
Head: 1st, 2nd and 3rd pharyngeal arch,
forebrain, site of lens placode, site of otic
placode, stomodeum
Body:
heart, liver, umbilical, early upper limb bulge
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Stage 13 contnd
Features
day 26, 27 somites, forebrain, site of lensplacode, site of otic placode , stomodeum, 1st
pharyngeal arch, 2nd pharyngeal arch, 3rdpharyngeal arch, heart prominence, somites
Identified: forebrain, site of lens placode, siteof otic placode, stomodeum, 1st pharyngealarch, 2nd pharyngeal arch, 3rd pharyngealarch, heart prominence, somite
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Stage 14
Facts
Week 5, 31 - 35 days, 5 - 7 mm
View: Lateral view. Amniotic
membrane removed.
EventsEctoderm: sensory placodes, lens
pit, otocyst, nasal placode,
primary/secondary vesicles, fourth
ventricle of brain,
Mesoderm: continued
segmentation of paraxial
mesoderm (more than 30 somite
pairs), heart prominence
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Stage 14 contnd
Head: 1st, 2nd and 3rd pharyngeal arch, forebrain, siteof lens placode, site of otic placode, stomodeum
Body: heart, liver, umbilical cord, mesonephric ridge
Limb: upper and lower limb buds
Features
midbrain, nasal placode, lens pit, 1,2,3 pharyngealarches, fourth ventricle of brain, 1st pharyngeal
groove, heart prominence, cervical sinus, upper limbbud, mesonephric ridge, lower limb bud, umbilicalcord.
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Stage 15
FactsFacts: Week 5, 35 - 38
days, 7 - 9 mm
Events
Ectoderm: sensory
placodes, lens pit,
otocyst, nasal pit,
primary/secondary
vesicles, fourth
ventricle of brain,Mesoderm: heart
prominence
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Stage 15 contd
Head: 1st, 2nd and 3rd pharyngeal arch, forebrain, siteof lens placode, site of otic placode, stomodeum
Body: heart, liver, umbilical cord, mesonephric ridge
Limb: upper and lower limb buds, hand plate
Features Identify: midbrain region, nasal pit, lens pit, 1st, 2nd
and 3rd pharyngeal arches, 1st pharyngeal groove,maxillary and mandibular components of 1st
pharyngeal arch, fourth ventricle of brain, heartprominence, cervical sinus, upper limb bud,mesonephric ridge, lower limb bud, umbilical cordLabelled Stage 15
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Stage 16
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Stage 16
FactsWeek 6, 37 - 42 days, 8 - 11 mm
Events
Ectoderm: sensory placodes, lens pit, otocyst,nasal pits moved ventrally, fourthventricle of brain
Mesoderm: heart prominence
Head: 1st, 2nd and 3rd pharyngeal arch, forebrain, eye, auricular hillocksBody: heart, liver, umbilical cord, mesonephric ridge
Limb: upper and lower limb buds, hand plate, developing arm
Features
Eye showing retinal pigment, nasolacrimal groove, nasal pit, fourth ventricle of brain,umbilical cord, 1st and 2nd pharyngeal arches, cervical sinus, heart, developing
arm with hand plate, foot plateIdentify: nasal pit, nasolacrimal groove, eye, 1st, 2nd and 3rd pharyngeal arches, 1st
pharyngeal groove, maxillary and mandibular components of 1st pharyngeal arch,auricular hillocks, fourth ventricle of brain, heart prominence, upper limb bud,mesonephric ridge, lower limb bud, umbilical cord Labelled Stage 16
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Stage 17
Facts
Week 6, 42 - 44 days, 11 - 14 mm
Events
Ectoderm: sensory placodes, lens pit,
otocyst,nasal pits moved ventrally, fourth
ventricle of brain
Mesoderm: heart prominence
Head: 1st, 2nd and 3rd pharyngeal arch,
forebrain, eye, auricular hillocks
Body: heart, liver, umbilical cord, mesonephric
ridge
Limb: upper and lower limb buds, hand digitalraysFeaturespigmented eye, nasal pit, nasolacrimal
groove, external acoustic meatus,
auricular hillock, heart, digital rays, liver
pronminance, thigh, ankle, foot plate,
umbilical cord
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Stage 18Facts
Week 7, 44 - 48 days, 13 - 17 mm
Events
Ectoderm: sensory placodes, lens pit,
otocyst,nasal pits moved ventrally, fourth
ventricle of brain
Mesoderm: heart prominenceHead: 1st, 2nd and 3rd pharyngeal arch,
forebrain, eye, auricular hillocks
Body: heart, liver, umbilical cord
Limb: upper and lower limb buds, foot plate,
wrist, hand plate with digital rays
Features
Identify: pigmented eye, eyelid, nasolacrimal groove, external acoustic meatus,
heart, digital rays, liver prominance, thigh, ankle, foot plate, umbilical cord
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Stage 19
Facts
Week 7, 48 - 51 days, 16 - 18 mm
Events
Ectoderm: sensory placodes, lens pit, otocyst, nasal
pits moved ventrally, fourth ventricle of brain
Mesoderm: heart prominence, ossification continues
Head: forebrain, eye, external acoustic meatus
Body:straightening of trunk, heart, liver, umbilical cord
Features
eyelid, eye, external acoustic meatus, auricle of
external ear, digital ray, wrist, liver prominence
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Stage 20
FactsWeek 8, 51 - 53 days, 18 - 22 mm
Events
Events Ectoderm: sensory placodes, lens pit,
otocyst, nasal pits moved ventrally, fourth
ventricle of brain
Mesoderm: heart prominence, ossificationcontinues
Head: forebrain, eye, external acoustic meatus
Features
scalp vascular plexus, eylid, eye, nose, external
acoustic meatus, auricle of external ear, arm,
elbow, wrist, liver prominence, digital rays
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Stage 21
Facts
Week 8, 53 - 54 days, 22 - 24 mm
Events
Ectoderm: sensory placodes, nasal pits moved
ventrally, fourth ventricle of brain
Mesoderm: heart prominence, ossificationcontinues
Head: nose, eye, external acoustic meatus
Body:straightening of trunk, heart, liver,
umbilical cord
Limb: upper limbs longer and bent at elbow,
foot plate with digital rays begin to separate,wrist, hand plate with webbed digits
Features
scalp vascular plexus, eylid, eye, nose, auricle
of external ear, arm, elbow, wrist, knee, notch
between digital rays, umbilical cord
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Stage 22
FactsWeek 8, 54 - 56 days, 23 - 28 mm
Events
Ectoderm:
Mesoderm: heart prominence, ossification
continues
Head: nose, eye, external acoustic meatusBody:straightening of trunk, heart, liver,
umbilical cord
Limb: upper limbs longer and bent at elbow,
foot plate with webbed digits, wrist, hand
plate with separated digits
FeaturesIdentify: straightening of trunk, pigmented
eye, eyelid, nose, external acoustic meatus, ear
auricle, scalp vascular plexus, separated digits
(fingers), thigh, ankle, umbilical cord
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Stage 23Facts
Week 8, 56 - 60 days, 27 - 31 mm
Events
Ectoderm:
Mesoderm: ossification continues
Head: eyelids, external ears, rounded head
Body: straightening of trunk, intestines
herniated at umbilicus
Limbs: hands and feet turned inward
Features
scalp vascular plexus, eylid, eye, nose, auricle
of external ear, mouth, sholder, arm, elbow,
wrist, toes separated, sole of foot, umbilical
cord
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