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S2 E2 KCU COB Andersen Courses > Embryology Lecture 10 Establishment of Body Plan II > Flashcards

Embryology Lecture 10 Establishment of Body Plan II Flashcards

1
Q

What are the three zones of the mesoderm?

A

Paraxial mesoderm
Intermediate Mesoderm
Lateral Plate mesoderm

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2
Q

What is described by a thick column of mesoderms, closest to and parallel with the notochord, and becomes segmented into somites?

A

Paraxial Mesoderm

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3
Q

What is described by a narrow column of mesoderm, lateral to the paraxial mesoderm, and gives rise to urogential system?

A

Intermediate mesoderm

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4
Q

What is described by a thing plate of mesoderm, lateral to intermediate mesoderm, splits to form the lining of body cavities and mesoderm of most internal organs as well as limbs?

A

Lateral plate mesoderm

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5
Q

Where do the somitomeres begin to develop and where are they added?

A

Develop in the paraxial mesoderm and new ones are added caudally

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6
Q

What event happens simultaneously as somites are being created?

A

Creation of new somitomeres at the anterior end of the primitive node (primitive streak: caudal end)

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7
Q

How many pairs of somitomeres are kept constant at the caudal end of the paraxial mesoderm?

A

11 pairs (Possible 12)

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8
Q

Which vertebrae are made from the cells migrating through the primitive streak?

A

Cervical, thoracic, and lumbar vertebrae

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9
Q

At what point does the somitomere become a somite?

A

At the 7th somitomere at the expense of the 8th

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10
Q

Cells migrating from the tail bud will form ____

A

The sacrum and coccyx

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11
Q

What are the 4 steps of somite history and organization?

A
  1. Epithelial Stage
  2. Epitheliomesenchymal Transformation stage
  3. Separation of the myotome
  4. Breakup of epithelial dermatome into dermal fibroblasts
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12
Q

What is happening during the epithelial stage of somite organization?

A

Cells are bunched together

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13
Q

What is happening during the epitheliomesenchyal transformation stage of somite organization?

A

Some of the cells lose their binding to each other

They become more mobile and diffuse out

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14
Q

What happens during the separation of the myotome during somite organization?

A

Split up into three regions

Dermatome, myotome, and sclerotome

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15
Q

What signaling balance causes myotome portion to commit to the myogenic lineage?

A

Shh from the notochord and Wnt from the dorsal tube

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16
Q

What is the function of BMP-4 and what inhibits it?

A

Stimulates somites to migrate to the limb bud

Inhibited by Noggin

17
Q

What signaling molecule from the myotome tells the sclerotome to produce scleraxis?

A

FGF

18
Q

What is the purpose of scleraxis

A

Causes the anterior and posterior border of somties to form the syndetome (The precursor of tendons)

19
Q

What creates gaps that allow nerves to grow in the neural tube?

A

Sclerotomal break up

It breaks up into an anterior and posterior portion

20
Q

In sclerotomal breakup, what portions fuse?

A

The posterior portion fuses with the adjacent anterior portion

21
Q

What model of somite differentiation is described below?
Be able to pick out the defining characteristics.
-Expressed along a timeline: 90 minutes/somite
-At each critical location that will serve to divide adjacent somites, lunatic fringe will become more concentrated at the future anterior border of a somite and c-hairy will be concentrated at the future posterior border of a somite

-cells at the anterior border will express Eph A (receptor)
-cells at the posterior border will express Eph B (ligand)
(These two will result in a fissure between the two adjacent somites)

A

Segmental Clock model

Refer to fig. 6.9

22
Q

What model of somite differentiation is described below?
Be able to pick out the defining characteristics.

  • There is an increase in [FGF-8] that leads to mitosis in the mesenchymal cells in posterior PRIMITIVE STREAK
  • Increase in [RETINOIC ACID] more anteriorly as opposed to FGF-8 (which opposes mitosis)
  • A balance becomes of the two which leads to a determination front. (this then leads to differentiation)
  • Mesp-2 is expressed because of the balance
A

Wavefront Mechanism

23
Q

Retinoic acid opposes what in the wavefront mechanism of somite differentiation?

A

FGF-8 which leads to the inhibition of mitosis

24
Q

What is cessation of somitogenesis?

A

A balance between FGF-8 and Retinoic Acid in the wavefront model of somite differentiation

25
Q

What are the steps in somite differentiation?

A
  1. Ectoderm dorsal to somites –> Wnt -6 –> Paraxis in somite
  2. Paraxis + decrease in Snail –> Mesenchymal cell to epithelial cell conversion
  3. Formation of somitocoel
  4. Notochord –> Shh + Noggin –> Pax1 + Pax9 in ventral part of somite
    (=sclerotome: Note that it forms around the notochord)
  5. Wnt genes in dorsal neural tube –> transformation of dorsal half of somite into dermomyotome
  6. Demomyotome –> Expression of Pax3, Pax7, paraxis –> Separation of dermomyotome into dorsal and ventral myotome
26
Q

What does the future intermediate mesoderm respond to?

A

BMP from lateral ectoderm
Activin from paraxial mesoderm
These two will make it become the intermediate mesoderm

27
Q

What does the intermediate mesoderm express?

A

Pax-2

28
Q

What is the intermediate mesoderm associated with?

A

The formation of pronephros and, later, the mesonephros

29
Q

What is the cranial and caudal extent dependent on in the intermediate mesoderm?

A

Hox-4 through Hox-11 genes

Think Hox genes

30
Q

What does the formation of the heart arise from?

A

Epiblast

31
Q

In the formation of the heart, cells that migrate through the ANTERIOR part of the primitive streak become____

A

The outflow track

32
Q

In the formation of the heart, cells that migrate through the MIDDLE part of the primitive streak become____

A

Ventricles

33
Q

In the formation of the heart, cells that migrate through the POSTERIOR part of the primitive streak become____

A

Atria

34
Q

What are the steps in heart formation?

A
  1. Anterior visceral endoderm is acted upon by BMPs and FGFs
  2. Cardiac Crest forms
    (movement through the anterior, middle, and posterior primitive streak)
  3. Expression of Nkx2-5, MEF2, and GATA4 genes
    Expression of these genes by cells allow for heart formation
35
Q

What are the cardiac tubes?

A

Bilaterally paired tubes that form the cariogenic mesoderm (Fuse beneath foregut to form one tube)`

36
Q

What are the two layers of the cardiac tube?

A

Inner layer: Endocardium
Outer layer: Myocardium
Cardiac Jelly forms between them (A specialized matrix)

37
Q

What is the source of pericardium and myocardium fibroblasts?

A

Proepicardial primordium

S2 E2 KCU COB Andersen Courses (14 decks)

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