2 - early changes in the embryonic disk

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A. The embryonic disk A. The embryonic disk 1. Definition1. Definition2. Significance2. Significance

B. Establishment of the germ layers (gastrulation)B. Establishment of the germ layers (gastrulation)1. Endoderm1. Endoderm

a. Migration of hypoblasts (primitive endoderm)a. Migration of hypoblasts (primitive endoderm) b. Early yolk sac (extraembryonic entoderm) b. Early yolk sac (extraembryonic entoderm)

2. Mesoderm2. Mesoderma. Primitive node (primitive knot)a. Primitive node (primitive knot)

b. Primitive streak b. Primitive streak

c. Primitive pitc. Primitive pitd. Primitive grooved. Primitive groovee. Notochord (notochordal process)e. Notochord (notochordal process)f. Migration and spread of mesodermf. Migration and spread of mesodermg. Intraembryonic vs. extraembryonic mesodermg. Intraembryonic vs. extraembryonic mesodermh. Significance and fate of notochord and primitive streak h. Significance and fate of notochord and primitive streak

3. Ectoderm (intra- versus extraembryonic)3. Ectoderm (intra- versus extraembryonic)

C. General significance of germ layersC. General significance of germ layers1. Ectoderm - differentiates into covering of body, nervous tissue, etc.1. Ectoderm - differentiates into covering of body, nervous tissue, etc.2. Mesoderm - differentiates into connective tissues, muscle, bone, etc.2. Mesoderm - differentiates into connective tissues, muscle, bone, etc.3. Endoderm - differentiates into lining of tubular digestive system, hepatocytes, etc.3. Endoderm - differentiates into lining of tubular digestive system, hepatocytes, etc.

Dr. H. Bragulla, DVM, Ph. D., 2005Dr. H. Bragulla, DVM, Ph. D., 2005


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D. Formation of the neural tubeD. Formation of the neural tube1. Neural plate1. Neural plate2. Neural groove2. Neural groove3. Neural folds3. Neural folds4. Neural crest4. Neural crest5. Significance5. Significance

E. Mesodermal structuresE. Mesodermal structures1. Paraxial mesoderm,1. Paraxial mesoderm,

i.e., somitesi.e., somitesa. Dermatomesa. Dermatomes

b. Myotomes b. Myotomesc. Sclerotomesc. Sclerotomes

2. Intermediate mesoderm2. Intermediate mesoderm3. Lateral mesoderm3. Lateral mesoderm4. Formation of the Coelom4. Formation of the Coelom

I. Splitting of the lateral mesodermI. Splitting of the lateral mesoderma. Somatic mesoderma. Somatic mesoderm

b. Splanchnic mesoderm b. Splanchnic mesodermII. SomatopleureII. SomatopleureIII. SplanchnopleureIII. SplanchnopleureIV. Significance of the coelomIV. Significance of the coelom

5. Significance5. Significance



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A. The embryonic disk, i.e., the embryoblast and extraembryonic membranesA. The embryonic disk, i.e., the embryoblast and extraembryonic membranes1. Definition: Accumulation of blastomers1. Definition: Accumulation of blastomers

(micro- and macromers, i.e., epi- and hypoblast or ecto- and entoblast)(micro- and macromers, i.e., epi- and hypoblast or ecto- and entoblast)2. Significance: Stem cells for the formation of the embryo and the yolk sac, the amnion,2. Significance: Stem cells for the formation of the embryo and the yolk sac, the amnion,

the chorion as well as the allantoisthe chorion as well as the allantois



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B. Establishment of theB. Establishment of the germ layers

germ layers ((GastrulationGastrulation ))a. Primitive streak a. Primitive streak

b. Primitive node (primitive knot) b. Primitive node (primitive knot)c. Primitive pitc. Primitive pitd. Primitive grooved. Primitive groove

1. Endoderm1. Endoderm

a. Migration of hypoblastsa. Migration of hypoblasts(primitive endoderm)(primitive endoderm)

b. Early yolk sac b. Early yolk sac

2. Mesoderm2. Mesoderma. Notochord (notochordala. Notochord (notochordal

process) process) b. Migration and spread of b. Migration and spread of

mesodermmesodermI. paraxialI. paraxialII. intermediateII. intermediateIII. lateralIII. lateral

c. Intraembryonic vs.c. Intraembryonic vs.extraembryonic (lateral)extraembryonic (lateral)

mesodermmesodermd. Significance and fate of d. Significance and fate of

notochord and primitive streak notochord and primitive streak

3. Ectoderm3. Ectoderm



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Gastrulation (1): Epiblast (= ectoblast)a. Primitive streak

b. Primitive node (primitive knot)c. Primitive pitd. Primitive groove

TransverseTransverse

LongitudinalLongitudinal



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Gastrulation (2): Migration and spread of mesoderm

I. paraxialII. intermediateIII. lateral

Intraembryonicvs.extraembryonic(lateral) mesoderm



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Gastrulation (3)Gastrulation (3)

Drawing of a pig embryo about 12 days old. TheDrawing of a pig embryo about 12 days old. Theends of the long blastocyst have been cut off.ends of the long blastocyst have been cut off.


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C. GeneralC. General significancesignificance of of germ layersgerm layers (stem cells of tissues)(stem cells of tissues)

1. Ectoderm -1. Ectoderm -differentiates into covering of body,differentiates into covering of body,nervous tissue, etc.nervous tissue, etc.

2. Mesoderm -2. Mesoderm -differentiates into connective tissues,differentiates into connective tissues,muscle, bone, etc.muscle, bone, etc.

3. Endoderm -3. Endoderm -differentiates into lining of tubular differentiates into lining of tubular digestive system, hepatocytes, etc., asdigestive system, hepatocytes, etc., aswell as of the tubular system of thewell as of the tubular system of thelarynx, trachea, and lungs, and others.larynx, trachea, and lungs, and others.

Redrawn by Dr. D. J. Hillmann, 2004 Dr. H. Bragulla, DVM, Ph. D., 2005Dr. H. Bragulla, DVM, Ph. D., 2005


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D. Formation of the neural tube,D. Formation of the neural tube,i.e.,i.e., neurulationneurulation ::

Organisator/inductor:Organisator/inductor: Notochord Notochord !!

1. Neural plate (head and trunk)1. Neural plate (head and trunk)2. Neural groove2. Neural groove3. Neural folds3. Neural folds4. Neural tube with the rostral and4. Neural tube with the rostral and

the caudal neuroporusthe caudal neuroporus

5. Neural crest (head and trunk)5. Neural crest (head and trunk)

6. Significance:6. Significance:A: Neural tube: CNS, i.e., brain andA: Neural tube: CNS, i.e., brain andspinal cordspinal cordB: Neural crest: PNS, i.e., spinalB: Neural crest: PNS, i.e., spinalganglia, peripheral nerves withganglia, peripheral nerves withneura and Schwann cells,neura and Schwann cells,sympathetic nerves, melanocytes,sympathetic nerves, melanocytes,Merkel cells, sacral part of theMerkel cells, sacral part of the

parasympathetic nervous system, parasympathetic nervous system,neural crest cells in various organsneural crest cells in various organsand vessels.and vessels.



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NeurulationNeurulation ::Formation of theFormation of theneural tube and somiteneural tube and somiteformationformation

Drawings from transverse sections of pigDrawings from transverse sections of pigembryos to show the formation and theembryos to show the formation and theearly differentiation of somites:early differentiation of somites:(A) Beginning of somite formation;(A) Beginning of somite formation;(B) seven-somite embryo.(B) seven-somite embryo.


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E. Mesodermal structuresE. Mesodermal structures1. Somites1. Somites

a. Dermatomesa. Dermatomes b. Myotomes b. Myotomesc. Sclerotomesc. Sclerotomesd. Somitocoeld. Somitocoel

2. Intermediate mesoderm2. Intermediate mesoderma. Kidneysa. Kidneys

b. Genital ridge b. Genital ridge3. Lateral mesoderm3. Lateral mesoderm

a. parietala. parietal

b. visceral b. visceralc. Coelomc. Coelom

4. Formation of the celom4. Formation of the celoma. Splitting of the laterala. Splitting of the lateral

mesodermmesoderm b. Somatopleure, i.e., the b. Somatopleure, i.e., the

parietal pleura, the parietal parietal pleura, the parietal pericardium serosum, and the pericardium serosum, and the parietal peritonaeum as well as the parietal peritonaeum as well as the

internal fascia of the trunc, i.e. theinternal fascia of the trunc, i.e. thesomatic mesodermsomatic mesodermc. Splanchnopleure, i.e., visceralc. Splanchnopleure, i.e., visceralserosa and splanchnic mesodermserosa and splanchnic mesoderm



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F. SignificanceF. Significance

1a. Dermis, subcutis, Fascia trunci externa1a. Dermis, subcutis, Fascia trunci externa1b. Skeletal muscles1b. Skeletal muscles1c. Cartilages and bones of the trunk and the of the1c. Cartilages and bones of the trunk and the of the

base of the skull, as well as of the limbs base of the skull, as well as of the limbs

2. Kidneys, gonads, ducts, etc.2. Kidneys, gonads, ducts, etc.

3a. Fascia trunci interna, parietal serosa3a. Fascia trunci interna, parietal serosa

3b. Visceral serosa, Tunica muscularis, Tela3b. Visceral serosa, Tunica muscularis, Telasubmucosa, Lamina muscularis mucosae, Laminasubmucosa, Lamina muscularis mucosae, Lamina

propria mucosae propria mucosae

4. Intraembryonic coelom: Cavum pleurae, Cavum4. Intraembryonic coelom: Cavum pleurae, Cavum pericardii, Cavum peritonaei pericardii, Cavum peritonaeiExtraembryonic celom: replaced by the allantoisExtraembryonic celom: replaced by the allantoisand by the amnion with the growing embryo insideand by the amnion with the growing embryo inside

E. Mesodermal structuresE. Mesodermal structures1. Somites1. Somites

a. Dermatomesa. Dermatomes b. Myotomes b. Myotomesc. Sclerotomesc. Sclerotomes

2. Intermediate mesoderm2. Intermediate mesoderm

3. Lateral mesoderm3. Lateral mesoderma. parietala. parietal

b. visceral b. visceral

4. Formation of the coelom4. Formation of the coelomSplitting of the lateral mesodermSplitting of the lateral mesodermI. Somatic mesodermI. Somatic mesoderm

(Somatopleure)(Somatopleure)II. Splanchnic mesodermII. Splanchnic mesoderm

(Splanchnopleure)(Splanchnopleure)



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Derivatives of the somites, i.e. the segmental paraxial mesoderm:Derivatives of the somites, i.e. the segmental paraxial mesoderm:a) Ventromedial: Sclerotomea) Ventromedial: Sclerotome

b) Dorsolateral: Dermatomyotome b) Dorsolateral: Dermatomyotome b 1) Dermatome (superficial): Dermis, Subcutis, external fascia of the trunk b 1) Dermatome (superficial): Dermis, Subcutis, external fascia of the trunk b 2) Myotome (deep): Myoblasts, forming myotubes, developing into sceletal b 2) Myotome (deep): Myoblasts, forming myotubes, developing into sceletal

muscle cells (striated), postmitotic cellsmuscle cells (striated), postmitotic cells



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Sclerotome:Sclerotome:Resegmentation of the caudal and the following cranial part of the sclerotome forming a vertebraResegmentation of the caudal and the following cranial part of the sclerotome forming a vertebra



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Derivatives of the somites, i.e.,Derivatives of the somites, i.e.,

of the sclerotome, of the myotome and of the dermatome, as well as of the somatic mesodermof the sclerotome, of the myotome and of the dermatome, as well as of the somatic mesoderm



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Some questions:Some questions:

1) The three germ layers in an embryo are:1) The three germ layers in an embryo are:a) epidermis, dermis, and subcutisa) epidermis, dermis, and subcutis

b) epicardium, myocardium, and endocardium b) epicardium, myocardium, and endocardium

c) ectoderm, mesoderm, and entodermc) ectoderm, mesoderm, and entoderm2) The development of the stem cells of the nerve tissue (neurulation) is induced by:2) The development of the stem cells of the nerve tissue (neurulation) is induced by:a) notochorda) notochord

b) entoderm b) entodermc) primitive streak c) primitive streak

3) The three parts of the germ layer in-between the ectoderm and the entoderm are:3) The three parts of the germ layer in-between the ectoderm and the entoderm are:a) the dorsal, the lateral, and the cranial mesenchymea) the dorsal, the lateral, and the cranial mesenchyme

b) the paraxial, intermediate, and the lateral mesoderm b) the paraxial, intermediate, and the lateral mesodermc) the inner, the outer, and the extraembryonic cell massc) the inner, the outer, and the extraembryonic cell mass

4) The space in-between the somatopleure and the splanchnopleure is:4) The space in-between the somatopleure and the splanchnopleure is:a) the primitive guta) the primitive gut

b) the celom b) the celomc) the yolk sacc) the yolk sac

5) The three parts of the segmented paraxial mesoderm (somite) are:5) The three parts of the segmented paraxial mesoderm (somite) are:a) the sclerotome, the myotome, and the dermatomea) the sclerotome, the myotome, and the dermatome

b) the ectoderm, the mesoderm, and the entoderm b) the ectoderm, the mesoderm, and the entodermc) the epiblast, the mesoblast, and the endoblastc) the epiblast, the mesoblast, and the endoblast



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Some more questions:Some more questions:

6) The skeletal muscles are characterized by6) The skeletal muscles are characterized bya) the striationa) the striation

b) the innervation b) the innervation

c) the sizec) the size7) The splanchnic mesoderm will provide7) The splanchnic mesoderm will providea) the nerve cells of the guta) the nerve cells of the gut

b) the epithelium of the gut b) the epithelium of the gutc) the connective and muscular tissues as well as the serosa of the gutc) the connective and muscular tissues as well as the serosa of the gut

8) The sclerotome cells will develop into8) The sclerotome cells will develop intoa) the bones of the trunca) the bones of the trunc

b) the bones of the heart and in the penis b) the bones of the heart and in the penisc) the bones of the jawsc) the bones of the jaws

9) The nervous tissue derives from9) The nervous tissue derives froma) entodermal stem cellsa) entodermal stem cells

b) mesoderm stem cells b) mesoderm stem cellsc) ectodermal stem cellsc) ectodermal stem cells

10) The development of the fertilized ovum into an embryo is divided (for descriptive purposes) into10) The development of the fertilized ovum into an embryo is divided (for descriptive purposes) intoa) gastrulation, neurulation, and cleavagea) gastrulation, neurulation, and cleavage

b) cleavage, neurulation, and gastrulation b) cleavage, neurulation, and gastrulationc) cleavage, gastrulation, and neurulationc) cleavage, gastrulation, and neurulation


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Some answers:Some answers:

1 c1 c

2 a2 a

3 b3 b4 b4 b

5 a5 a

Redrawn by Dr. D. J. Hillmann, 2004 Dr. H. Bragulla, DVM, Ph. D., 2005Dr. H. Bragulla, DVM, Ph. D., 2005

6 b6 b7 c7 c

8 a8 a

9 c9 c

10 c10 c

2 - early changes in the embryonic disk

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