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Embryology > Lecture 4 (musculoskeletal development) > Flashcards

Lecture 4 (musculoskeletal development) Flashcards

1
Q

Which germ layer gives rise to the most body parts?

A

mesoderm

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2
Q

Which type of mesoderm is the greatest contributor to body parts?

A

paraxial (somitic) mesoderm

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3
Q

What gives rise to segmented epithelial somites?

A

paraxial mesoderm

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4
Q

What are the 4 types of somites? What does each give rise to?

A
  1. dermatome -> dermis of back
  2. myotome -> skeletal muscle
  3. syndetome -> tendons
  4. sclerotome -> vertebrae, ribs, cartilage
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5
Q

What day does the 1st somite appear?

A

around day 20

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6
Q

How do somites appear?

A

ordered sequence cranial to caudal along neural tube

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7
Q

A new somite arises once every:

A

90 minutes

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8
Q

The neural tube begins to close at which somite level?

A

4th

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9
Q

How many pairs of somites exist?

A

44

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10
Q

Somites differentiate into what two types?

A

sclerotome and demomyotome

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11
Q

Upper and lower halves of __________ form vertebrae during the _____ wk.

A

sclerotome, 4th

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12
Q

Dermomyotome divides in:

A

dermotome and myotome

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13
Q

What two components does myotome become?

A
  • epaxial division (dorsal side)

- hypaxial division (ventral side)

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14
Q

What are the three muscle types? What do they form from?

A
  1. skeletal -> paraxial
  2. smooth -> splanchic (visceral) layer of lateral plate mesoderm
  3. cardiac -> splanchic (visceral) layer of lateral plate mesoderm
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15
Q

The epaxial division of the myotomes become: ________. What innervates these?

A

muscles of back and neck

dorsal primary ramus

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16
Q

The hypaxial division of the myotomes become: ________. What innervates these?

A

trunk, back, and limb muscle

ventral primary ramus

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17
Q

What role does BMP4 play in somite differentiation?

A

produced by ectodermal region and activates WNT from neural tube

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18
Q

In somite differentiation, the notochord releases ___________. This leads to:

A

SHH and Noggin

formation of sclerotome and expression of PAX1 (vertebral formation)

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19
Q

WNT and SHH acting on somites produce lead to expression of ________ and formation of:

A

PAX3

dermatome

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20
Q

WNT and SHH act on the epaxial region of myotome to express:

A

MYF5

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21
Q

WNT and BMP4 act on the hypaxial region of myotome to express:

A

MYOD

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22
Q

MYF5 and MYOD are:

A

transcription factors that activate pathways for muscle development

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23
Q

Hox genes are for:

A

patterning of axes and the vertebrae

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24
Q

Vertebrae are formed by:

A

fusion of the upper and lower halves of two successive sclerotomes

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25
Q

What are the two types of bone formation?

A

endochondrial ossification

intramembranous ossification

26
Q

Outline steps to endochondrial ossification:

A
  1. mesenchymal cells in sclerotomal core condense and commit to cartilage lineage
  2. chondrocytes condense to form template (6th wk)
  3. chondrocytes in center express VEGF and undergo apoptosis
  4. extracellular matrix of apoptotic cells mineralize
  5. blood vessels invade space, osteoblasts differentiation
27
Q

What happens in premature bones once osteoblasts differentiate?

A
  • osteoblasts secrete mineral matrix on template
  • continues
  • blood vessel enters @ secondary sites and start other ossification centers
  • epiphyseal plate continues to produce cartilage
28
Q

Endochondrial ossification allows for what w/ long bones? How long does it continue?

A
  • allows for long bones to lengthen

- continues until 20 years old roughly

29
Q

What occurs in intramembranous ossification? Does it require a cartilage template?

A

mesenchymal cells directly differentiate into osteoprogenitor cells

no template

30
Q

What two structures are formed through intramembranous oss?

A
  1. neurocranium

2. viscerocranium (face)

31
Q

The neurocranium consists of what two things?

A
  • membranous neurocranium (flat bones)

- cartilaginous neurocranium (base of skull)

32
Q

The viscerocranium originates from what cell type?

A

neural crest cells

33
Q

the membranous neurocranium is derived from:

A

neural crest cells and paraxial mesoderm

34
Q

The fissures that separate the flat bones of the skull are called:

A

sutures

35
Q

what are fontanels?

A

areas of the skull where >2 sutures meet

36
Q

When do sutures usually close?

A

during 1st or 2nd year of life

37
Q

What is craniosynostosis? What’s a major cause?

A

premature closure of at least one cranial suture

mutations in FGFRs

38
Q

Scaphocephaly is a result of:

A

premature closure of sagittal suture

39
Q

Brachycephaly is a result of:

A

premature closure of coronal suture

40
Q

Plagiocephaly is a result of:

A

premature closure of unilateral coronal and lamboid sutures

41
Q

Cloverleaf skull is a result of:

A

premature closure of most cranial sutures

42
Q

When do limb buds become visible?

A

by wk 5

43
Q

Limb development begins with the formation of the:

A

apical ectoderm ridge (AER)

44
Q

What initiates limb outgrowth?

A

FGF10 secreted by lateral plate mesoderm

45
Q

What molecules lead to AER formation?

A

induced by bMP and restricted to distal portion of radical fringe -> induces SER-2 expression in cells destined to b AER

46
Q

What molecules does the AER express to maintain progress/undifferentiated zone?

A

FGF4 and FGF8

47
Q

What molecule is antagonistic to FGF and produced by differentiated cells?

A

retinoic acid

48
Q

In limb development, RA is expressed in which region?

A

stylopod

49
Q

In limb development, Shh is expressed in which region?

A

Zuegopod

50
Q

The autopod is differentiated thanks to this molecule:

A

FGF

51
Q

the AER creates separate digit ridge by day:

A

48

52
Q

digits begin to separate by day _____ thanks to:

A

51, cell death

53
Q

digit separation is complete by day ______.

A

56

54
Q

What region of the limb is responsible for anterior-posterior patterning?

A

ZPA

55
Q

What molecule does the ZPA produce? Do higher levels lead to anterior or posterior digits?

A

Shh

posterior

56
Q

When does limb rotation occur?

A

8th week

57
Q

The upper limbs rotate:

A

laterally

58
Q

Lower limbs rotate:

A

medially

59
Q

TBX5 leads to development of the _____limb.

A

fore

60
Q

TBX4 leads to development of the ____limb.

A

hind

Embryology (8 decks)

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