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Microanatomy > Mesoderm (3 germ layers) > Flashcards

Mesoderm (3 germ layers) Flashcards

1
Q

Gastrulation

A

Begins with the formation of the P.S.
Ends with the formation of the 3 embryonic germ layers (ectoderm, endoderm and mesoderm)

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2
Q

Delamination

A

Detachment of blastomeres from inner cell mass into blastocoel forming hypoblasts
Remaining cells proliferate and form epiblast (source of germ layers)

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3
Q

Hypoblast

A

Detached cells that line the inner side of blastocoel
Presumptive endoderm cells
Line the yolk sac

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4
Q

Epiblast

A

Remaining cells of the inner cell mass
Gives rise to the ectoderm and mesoderm

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5
Q

Formation of the mesoderm

A

Proliferation of epiblast cells
Cells move through the P.S. occupying the space ebtween epiblast and hypoblast
Formed first caudally then expands laterally and cranially

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6
Q

What does the mesoderm expand to form?

A

Paraxial
Intermediate
Lateral (splanchnic and somatic)
Extraembryonic

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7
Q

How is the cr. mesoderm formed?

A

Accumulation of multipotential cells at the cr. end of the P.S.
Forms Hansen’s/ Primitive Node, head mesoderm and plays a role in forming the notochord

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8
Q

Extraembryonic mesoderm

A

Expands between the trophoblast and extraembryonic endoderm
Continuous with embryonic germ layers

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9
Q

Where is the rate of mesoderm expansion the slowest?

A

In horses

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10
Q

Early embryo

A

Mesoderm is a loose aggregation of cells (mesenchyme)

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11
Q

Later embryo

A

Differentiation begins
Mesodermal “fate map” is possible

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12
Q

Lateral mesoderm

A

Lateral plate splits to form somatic and splanchnic mesoderm
Cavity between the two is coelom

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13
Q

Somatic mesoderm

A

Somatopleure (mesoderm + ectoderm)
Parietal
Forms pelvic and shoulder girdles, long bones of the limbs, sternum

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14
Q

Splanchnic mesoderm

A

Splanchnopleure (mesoderm + endoderm)
Visceral
Must be present for BVs to form
GI tract of thorax and abdomen

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15
Q

Intermediate mesoderm

A

Runs lengthwise along the entire “trunk” of the embryo
Later in development cell clusters (nephrotomes) and nephrogenic cord form

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16
Q

What does the intermediate mesoderm give rise to?

A

Most but not all of the urinary system and parts of the reproductive system

17
Q

Paraxial mesoderm

A

Aggregation of mesoderm to form 2 parallel columns
Beginning cranially, transverse fissures appear and form somites

18
Q

What does the somite number indicate?

A

the age of embryo and is constant for a species

19
Q

Myotome

A

Forms skeletal muscles of body

20
Q

Dorsal (epaxial) part of myotome

A

Muscles of the back
Muscles of vertebral column dorsal to transverse process

21
Q

Ventral (hypaxial) part of myotome

A

Ventro-lateral muscles (intercostal and abdominal)
Limb muscles

22
Q

Formation of the multinucleate cell

A

Mesenchyme –> myogenic cells –> myoblast –> cells fusion to form multinucleate cell

23
Q

Sclerotome

A

Verterbrae and ribs

24
Q

Dermatome

A

Dermis (not epidermis)

25
Q

Mesoderm of the head

A

No lateral mesoderm or coelom
Mesoderm migrates to the “brachial arches”
Neural crest cells contribute (ectomesenchyme)

26
Q

Occipital somites

A

Somites that extend only into the cd. regions of the head

27
Q

Somitomeres

A

Rostral to occipital somites,
Formed by paraxial mesoderm
Extend only as far as the rostral extent of the notochord (cd. forebrain/ infundibulum)

28
Q

Skeletal system

A

Somatic mesoderm
Sclerotome
Occipital somites
Neural crest cells

29
Q

What do neural crest cells form?

A

Ectomesenchyme
Face and skull bones

30
Q

How are bones formed?

A

Via endochondral and intramembranous ossification

31
Q

Skeletal dysplasia

A

Cranio-facial defects- abnormal neural crest migration

32
Q

T/F: After the formation of the mesoderm, P.S. regresses and has no derivative structures in the adult

A

TRUE

33
Q

How is the notochord formed?

A

Mesodermal cells from Hensen’s node migrate toward the pre-cordal plate forming the notochordal plate
Plate folds to form notochord (solid mass of cells)
Formed cr. to cd. as the primitive streak regresses

34
Q

Function of the notochord

A

Inductor for ectoderm to form neuroectoderm (neural plate, CNS, somite)
Organizing center for vertebral bodies

35
Q

Formation of the neural tube

A

Thickening of the ectoderm overlying notochord neural plate
Folding of neural plate
Formation of neural tube

Microanatomy (18 decks)

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