Fate of Embryonic Tissues PDF
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The Fate ofEmbryonic
Tissues
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DEVELOPMENT OF
SYSTEMS AND ORGANS
During vertebrate gastrulation the three germ layerare formed .These differentiate , first into primordial cell massesand then into specific organs and tissues.During this process, cells become increasingly
committed to specific directions of differentiation.
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Ectoderm:
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Derivatives of Ectoderm:
The brain, spinal cord , and nearly all outer epithelial structures of the body develop fromprimitive ectoderm .They are among the earliest organs to appear.
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Derivatives of Ectoderm:Nervous System
o Just above thenotochord, theectoderm thickens
to form a neuralplate.
o The edges of thisplate rise up, fold,
and join together atthe top to create an
elongated, hollowneural tube.
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Derivatives of Ectoderm:Nervous System
o The neural tubegives rise to most ofthe nervous system:
o anteriorly it enlargesand differentiates
into the brain andcranial nerves
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Derivatives of Ectoderm:Nervous System
o The neural tubegives rise to most ofthe nervous system:
o posteriorly it formsthe spinal cord and
spinal motor nerves .
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Derivatives of Ectoderm:Nervous System
o Much of the rest ofthe peripheralnervous system is
derived from neuralcrest cells, which
pinch off from theneural tube before itcloses.
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Derivatives of Ectoderm:Nervous System
o Neural crest tissue isunique tovertebrates and was
probably of primeimportance in
evolution of thevertebrate headand jaws .
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Derivatives of Ectoderm:and other Tissues
Other tissues from theneural crest are:o portions of the
cranial nerveso pigment cells
o cartilage and boneof most of the skull
(including jaws)
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Derivatives of Ectoderm:and other Tissues
Other tissues from theneural crest are:
o ganglia of the ANSo medulla of the
adrenal glando other endocrine
glands
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How are the billions of nerveaxons in the body formed?
1907 embryologistHarrisonGrowing nerve axonterminated in a grow
cone , from which extenumerous tiny threadlikpseudopodial processes(filopodia)
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How are the billions of nerveaxons in the body formed?
cone is steered by an of guidance moleculessecreted along thepathway and by theaxons target. This
chemical guidancesystem, which must, ofcourse, be geneticalldirected
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Endoderm:
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Derivatives of Endoderm:Digestive Tube
In frog embryos theprimitive gut makes itsappearance duringgastrulation with the
formation of thearchenteron.
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Derivatives of Endoderm:Digestive Tube
From this simpleendodermal cavitydevelop the lining of the
digestive tract ,lining of the pharyn
lungs
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Derivatives of Endoderm:Digestive Tube
From this simpleendodermal cavitydevelop the lining of the
most of the liver apancreasthe thyroid andparathyroid glandsthe thymus .
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Derivatives of Endoderm:Digestive Tube
In other vertebrates thealimentary canal developsfrom the primitive gut and isfolded off from the yolk sacby growth and folding ofthe body wall
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Derivatives of Endoderm:Digestive Tube
The ends of the tube opento the exterior and arelined with ectoderm,whereas the rest of thetube is lined with
endoderm. Lungs, liver,and pancreas arise fromthe foregut.
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Derivatives of Endoderm:Survival of Gill Arches
Among the most intriguderivatives of the digesttract are the pharynpouches , which makappearance in the early
embryonic stages of allvertebrates
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Derivatives of Endoderm:Survival of Gill Arches
During development theendodermally-lined pharynpouches interact with overlyectoderm to form gill afishes , gill arches develop gills and supportive struc
and serve as respiratory
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Derivatives of Endoderm:Survival of Gill Arches
When early vertebrates moved onto land , gills were unsuitaaerial respiration and respiratory function was performed by
independently evolved lungs .
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Derivatives of Endoderm:Survival of Gill Arches
Although gill arches serve no respiratory function in either embryos or adults of terrestrial vertebrates, they are necessary primordial for a
variety of other structures .
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Mesoderm:
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Derivatives of Mesoderm:Support, Movement
The mesoderm formsmost skeletal andmuscular tissuesthe circulatorysystemurinary andreproductive organs
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Derivatives of Mesoderm:Support, Movement
As vertebrates haveincreased in size andcomplexity,mesodermally derivedsupportive , movement ,
and transport structureshave become an evengreater proportion ofthe body.
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Derivatives of Mesoderm:Support, Movement
Most musclesarise from themesoderm alongach side of the
neural tube
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Derivatives of Mesoderm:Support, Movement This mesoderm divide
a linear series of blocksomites (38 in hum
which by splitting, fuand migration becomthe axial skeletondermis of the dor
muscles of the babody walllimbs
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Derivatives of Mesoderm: theBeating Heart
Mesoderm gives riseto the first functionalorgan , theembryonic heart .
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Derivatives of Mesoderm: theBeating Heart
Guided by the underlyingendoderm, two clustersof pre-cardiacmesodermal cells moveameba like into position
on either side of thedeveloping gut.
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Derivatives of Mesoderm: theBeating Heart
These clusters differentiateinto a pair of double-walled tubes, which later fuse to form a single, thintube.
As the cells grouptogether, the firsttwitchings are evident.
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Derivatives of Mesoderm: theBeating Heart
In a chick embryo , a fa
animal for experimentalembryological studies, theprimitive heart begins to beon the second day of theday incubation period;it begins beating before atrue blood vessels have forand before there is any bloopump
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Derivatives of Mesoderm: theBeating Heart
As the ventricle primorddevelops , the spontaneoucellular twitchings becomcoordinated into a feeblrhythmical beat .
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Derivatives of Mesoderm: theBeating Heart
New heart chambers , each with a beat faster thanits predecessor, then develop.
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Derivatives of Mesoderm: theBeating Heart
Finally a specialized area of heart muscle calledthe sinoatrial (SA) node develops and takescommand of the entire heartbeat . The SA nodebecomes the hearts primary pacemaker.
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Derivatives of Mesoderm: theBeating Heart
As the heart builds astrong and efficientbeat, vascular channelsopen within the embryoand across the yolk.
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Derivatives of Mesoderm: theBeating Heart
Within the vessels are the first primitive blood cells suspended in plasmadevelopment of the heart and circulation is crucial to continued embryonicdevelopment, because without circulation an embryo could not obtain materials fogrowth .
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Derivatives of Mesoderm: theBeating Heart
Food is absorbed from the yolk and carried to the embryonic body , oxydelivered to all tissues, and carbon dioxide and other wastes are carried aembryo is totally dependent on these extraembryonic support systems, andcirculation is the vital link between them.
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The End