Somites and Embryonic Folding Flashcards

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1
Q

What are the three parts of the intraembryonic mesoderm?

A

paraxial mesoderm
intermediate mesoderm
lateral plate mesoderm

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2
Q

What is the paraxial mesoderm?

A

mesoderm lying either side of the notochord. Forms gut, axial skeleton, voluntary musculature, dermis

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3
Q

What is the intermediate mesoderm?

A

lateral to paraxial mesoderm. Forms urinary and genital

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4
Q

What is the lateral plate mesoderm?

A

remainder of lateral mesoderm.

  1. layer adjacent to ectoderm - somatopleuric mesoderm
  2. layer adjacent to endoderm - splanchnopleuric mesoderm
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5
Q

What does the somatopleuric mesoderm and splanchnopleuric mesoderm become?

A
  1. striated voluntary muscle

2. smooth muscle of the gut

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6
Q

What forms somites?

A

paraxial mesoderm

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7
Q

What do the medial, intermediate and later parts of the somite form?

A

medial - sclerotome
intermediate - myotome
lateral - dermatome

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8
Q

Derivatives of somites

A
3 occipital
8 cervical
12 thoraic
5 lumbar
5 sacral
1-5 coccygeal
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9
Q

What do somites do?

A

precursor populations of cells which receive a segmental spinal nerve which follows the tissure wherever it migrates

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10
Q

What is the intraembryonic coelom?

A

clefts in lateral plate mesoderm, infront of prochordal plate
fuses to form horse shape cavity

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11
Q

What happens in week 4?

A

rapid growth (particularly lengthwise) which allows lateral and longitudinal folding to occur

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12
Q

Which parts grow?

A

embryonic disc and amnion grow vigorously, but yolk sac hardly grows.
YS is attached ventrally to the embryo, lack of growth causes it to form a 3D cylinder

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13
Q

Why does growth mainly occur in the thin flexible outer rim of the embryo?

A

developing neural tube and somites stiffen the dorsal axis of the embryo

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14
Q

What occurs in longitudinal folding?

A
reversal
cranial end develops first 
rapid growth of neural tube
1,2,3,4,5 to 5,4,3,2,1
(brain, mouth, heart, diaphragm)
yolk sac pinched - endodermally lined tube (gut)
amniotic cavity enlarging lots
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15
Q

Lateral folding

A

edges of amnion grow downwards, putting pressure on the yolk sac
gut tube cut off and suspended in mesoderm
reduced comms between intra and EEM

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16
Q

What is the vitelline duct?

A

connection between gut tube and yolk sac

17
Q

What does ectoderm form?

A

skin

18
Q

What does mesoderm form?

A

dermatomes, own nerve supply