Embryology Nandini

8/4/2019 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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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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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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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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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


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


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

Embryology Nandini

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