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Embryonic Period

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All of the major organs systems begin to develop. Folding of the ... Auricular hillocks are distinct. Eyelids form in face. Seventh week. Umbilical herniation ... – PowerPoint PPT presentation

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Title: Embryonic Period


1
Embryonic Period
  • Montakarn Tansatit,MD.
  • Faculty of Medicine
  • Chulalongkorn University

2
Embryonic period
  • All of the major organs systems begin to develop
  • Folding of the embryo occurs
  • Embryo develops a distinct human appearance

3
Gastrulation
4
Gastrulation
  • is the process that establishes the three
    definitive germ layers of embryo
  • Ectoderm
  • Mesoderm
  • Endoderm
  • these three layers give rise to all the tissues
    and organs of the adult

5
Primitive streak
  • Consists of
  • primitive groove
  • primitive node
  • primitive pit

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Definitive germ layers
  • Ectoderm
  • Intraembryonic mesoderm
  • Endoderm

8
Changes involving ectoderm
  • Neuroectoderm
  • Neural crest
  • Neural tube
  • Surface ectoderm

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Neuroectoderm
  • 1. Neural crest
  • Spinal and autonomic ganglia
  • Ganglia of cranial nerves V, VII, IX and X
  • Schwann cells and meninges (pia and arachnoid)
  • Melanocytes
  • Medulla of suprarenal gland
  • Bones and connective tissues of craniofacial
    structures

11
Neuroectoderm
  • 2. Neural tube
  • Central nervous system
  • Retina
  • Posterior pituitary gland

12
Surface ectoderm
  • Epidermis of the skin and its appendages
  • Mammary glands
  • Anterior pituitary glands
  • Enamel of teeth
  • Inner ear
  • Lens

13
Changes involving endoderm
  • Endoderm is involved in the formation of the
  • Digestive system
  • Respiratory system
  • Urogenital system
  • Pharyngeal pouches

14
Changes involvingintraembryonic mesoderm
  • Paraxial mesoderm
  • Intermediate mesoderm
  • Lateral mesoderm

15
Paraxial mesoderm
  • is a thick plate of mesoderm on each side of the
    midline
  • becomes organized into segments known as
    somitomeres

16
Somitomeres
  • are rounded, whorl-like structures consist of
    disclike paraxial mesodermal cells
  • form in a craniocaudal sequence
  • somitomeres 1-7 do not form somites but
    contribute mesoderm to the pharyngeal arches

17
Somitomeres
  • These 7 pairs of somitomeres give rise to the
    striated muscles of the face, jaw and throat
  • remaining somitomeres condense to form 42-44
    pairs of discrete blocks of segmental mesoderm
    called somites

18
Somites
  • first pair of somites forms on day 20 new
    somites appear at a rate of three per day
  • somites closest to the caudal end disappear to
    give a final count of approximately 35 pairs of
    somites
  • number of somites is one of the criteria for
    determining age of the embryo during embryonic
    period

19
Somites
  • Somites further differentiate into these
    components
  • 1. Sclerotome - cartilage and bone component
  • 2. Myotome - muscle component
  • 3. Dermatome - dermis of skin component

20
Intermediate mesoderm
  • connects the paraxial mesoderm and lateral
    mesoderm
  • urogenital ridges (future kidneys and gonads)

21
Lateral mesoderm
  • is a thin plate of mesoderm
  • intraembryonic coelom forms, diving the lateral
    mesoderm into 2 layers
  • 1. Intraembryonic somatic mesoderm
  • 2. Intraembryonic visceral mesoderm

22
Intraembryonic coelom
  • At the end of the third week intercellular clefts
    appear in the lateral mesoderm

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Intraembryonic coelom
  • begins when spaces coalesce within the lateral
    mesoderm and form a horseshoe-shaped space that
    opens into the extraembryonic coelom on the right
    and left side

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Intraembryonic coelom
  • Divides the lateral plate mesoderm into two
    layers
  • 1. Intraembryonic somatic mesoderm
  • 2. Intraembryonic visceral mesoderm

29
Notochord
  • is a solid cylinder mesoderm in the midline of
    the trilaminar embryonic disc

30
Notochord
  • is important for the following
  • 1. Induces the overlying ectoderm to
    differentiate into neuroectoderm to form the
    neural plate
  • 2. Induces the formation of the vertebral bodies
  • 3. Forms the nucleus pulposus of each
    intervertebral disc

31
Folding of the embryo
32
Folding of the embryo
  • Craniocaudal folding
  • is caused by the development of the central
    nervous system and amnion
  • Lateral folding
  • is caused by the development of the somites,
    amnion and other components of the lateral body
    wall

33
Craniocaudal folding
34
Craniocaudal folding
  • Cranial (head) folding
  • Caudal (tail) folding

35
Results
36
Results
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Lateral folding
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Results
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Highlights of embryonic period
49
Fourth week
  • Fusion of the neural folds begins
  • Neuropores are closed
  • Folding of the embryo

50
Fourth week
  • Oropharyngeal membrane ruptures
  • Upper limb buds appear
  • The otic pit develops and pharyngeal arches 12
    are visible on the surface

51
Fourth week
  • Cardiac loop begins to appear
  • Intermediate mesoderm becomes visible

52
Fifth week
  • Lens pits appear
  • Lower limb buds appear

53
Sixth week
  • Hand plates are forming
  • Retinal pigment is visible

54
Seventh week
  • Head is relatively larger and trunk is straighter
  • Finger rays become visible and toe rays begin to
    appear

55
Seventh week
  • Auricular hillocks are distinct
  • Eyelids form in face

56
Seventh week
  • Umbilical herniation
  • Urogenital membrane ruptures

57
Eighth week
  • The trunk is elongated and straightening
  • Upper limbs are longer and are bent at elbows
  • Hands approach each other at the midline
  • Eyelids and external ears are better developed

58
The end
The end
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