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MSCT > Musculoskeletal Embryology > Flashcards

Musculoskeletal Embryology Flashcards

1
Q

Embryo folding

A

Occurs between days 18-24 after fertilization, trilaminar embryo undergoes cranial-caudal and lateral folding

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2
Q

After folding - endoderm

A

The yolk sac becomes the gut tube and is suspended in the body cavity, will become the epithelial lining of the gut

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3
Q

After folding - mesoderm

A

Suspends gut tube within tube of the body and surrounds the gut tube, will become the wall of the gut. and under the ectoderm will become the components of the body wall and limbs

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4
Q

After folding - ectoderm

A

Brought around the embryo with mesoderm to form anterior body wall and encase embryo in amniotic cavity, will become the epithelium of the skin

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5
Q

Paraxial mesoderm

A

On either side of the neural tube, forms the axial skeleton and skeletal muscle in the body wall and limbs

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6
Q

Intermediate mesoderm

A

Next to the the paraxial mesoderm

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7
Q

Lateral plate mesoderm

A

Lateral to the intermediate mesoderm, divided into somatic mesoderm and splanchnic mesoderm

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8
Q

Somatic mesoderm

A

In contact with ectoderm, and will form the connective tissue and smooth muscle of then body wall and limbs, as well as the appendicular skeleton

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9
Q

Splanchnic mesoderm

A

In contact with endoderm, and will form the wall of the gut

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10
Q

Limb development time and location

A

Between weeks 4-8 and from the lateral plate mesoderm

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11
Q

Limb embryonic induction

A

Intermediate mesoderm produces FGF8, which induces lateral plate to produce FGF10, which induces overlying ectoderm to form the apical ectoderm ridge (AER)

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12
Q

Apical ectodermal ridge

A

Thickened ectoderm, maintains proliferation of the progress zone (somatic mesoderm) by producing FGF4 and FGF8, promotes outgrowth of limb bud along proximal/distal axis (shoulder to fingers)

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13
Q

Cells leaving progress zone

A

As the limb elongates they are no longer under the control of AER and stop dividing and differentiate into cartilage and bone

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14
Q

Removal of AER

A

Results in distal truncation of the limb (meromelia or amelia)

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15
Q

Direction cells of the limb proliferate

A

Proximal to distal pattern

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16
Q

Selective loss of AER

A

How digits form, reduces amount of FGF in interdigital spaces, causing apoptosis and cessation of cell proliferation

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17
Q

Zone of polarizing activity

A

Specialized mass of cells in base of limb bud that regulate development along cranial/caudal axis

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18
Q

ZPA role in maintaining AER

A

Induced by FGF8, produces retinoic acid which initiates expression of SHH to regulate the anteroposterior axis

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19
Q

Sonic hedgehog

A

Establishes gradient of homeobox gene expression across developing limb

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20
Q

Hox genes

A

Transcription factors that define pattern of differentiation from thumb to little finger

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21
Q

Polydactyly

A

Formation of extra digits due to transplantation of the ZPA or implantation of a Shh ectopically expressed in anterior limb bud (as well as the usual posterior expression)

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22
Q

Two methods by which bones develop

A

Intramembranous or endochondral ossification

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23
Q

Intramembranous ossification bones formed

A

Flat bones of the skull and bones of the face

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24
Q

Intramembranous ossification mesenchyme cell characteristics

A

Loosely organized, mainly mesodermal embryonic tissue that will develop into connective and skeletal tissues (like blood and lymph)

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25
Q

Intramembranous ossification mesenchyme cell differentiation

A

Into osteoblasts that produce primary or woven bone (irregularly arranged collagen fibers)

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26
Q

Intramembranous ossification woven bone

A

Remodeled to lamellar bone (parallel alignment of collagen into sheets)

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27
Q

Endochondral ossification bones formed

A

Long bones, vertebral column, pelvis, sternum, skull base

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28
Q

Endochondral ossification mesenchyme cell differentiation

A

Into chondroblasts that produce a cartilage model

29
Q

Endochondral ossification cartilage

A

Becomes vascularized and is replaced by bone matrix

30
Q

Endochondral ossification remaining cartilage

A

Found at surface of epiphysis as articular cartilage, then between epiphysis and diaphysis as the epiphyseal plate

31
Q

Epiphyseal plate role

A

Regulates the growth in length of long bones

32
Q

Epiphyseal plate proliferation

A

Occurs at the epiphyseal side of plate, replacement by bone is on the diaphyseal side

33
Q

Epiphyseal plate bone growth duration

A

As long as the rate of cell division is equal to that of cell death and ossification, typically until the 20th year of life

34
Q

Somitomeres

A

Segments of paraxial mesoderm

35
Q

Somitomere mesoderm contributions

A

1-7 to the head and neck, the rest condense into somites

36
Q

Somites

A

Differentiate into sclerotome, myotome, and dermatome

37
Q

Sclerotome

A

Axial skeleton, formed by cells of the ventral and medial wall of somite that lose epithelial arrangement and migrate towards the notochord

38
Q

Dermomyotome

A

Remaining cells following sclerotome migration, will turn into dermatome and myotome

39
Q

Dermatome

A

White, dermis of skin

40
Q

Myotome

A

Red, skeletal muscle

41
Q

Myotome - two splits

A

Dorsal epimere, ventral hypomere

42
Q

Epimere

A

Develops into intrinsic back muscles

43
Q

Hypomere

A

Develops into limb and body wall muscles

44
Q

Dorsal and ventral condensation

A

Hypomere cells that migrate into the limb bud to become skeletal muscles of the limbs

45
Q

Dorsal condensation

A

Gives rise to extensor muscles

46
Q

Ventral condensation

A

Gives rise to flexor muscles

47
Q

Skeletal muscle differentiation cause

A

Caused by growth factors inducing the expression of transcription factors

48
Q

Skeletal muscle differentiation steps

A

Somatic epithelium, myogenic progenitor cells (mitotic phase), myoblast, myotube, myofiber with muscle satellite cells/stem cells (postmitotic phase)

49
Q

Growth factors in skeletal muscle differentiation

A

FGF, TGF-B

50
Q

Transcription factors in skeletal muscle differentiation

A

Myf-5, Pax-3

51
Q

Myf-5

A

Gives rise to Myogenin and MyoD

52
Q

Pax-3

A

Gives rise to MyoD

53
Q

MyoD

A

Gives rise to myoblast genes (actin, myosin) or myogenin

54
Q

Myogenin

A

Gives rise to myotube genes (troponin, tropo-myosin, etc) or MRF-4

55
Q

MRF-4

A

Gives rise to myofiber genes

56
Q

Axons of motor neurons

A

Enter limb bud in 5th week of development, grow into dorsal and ventral muscle masses

57
Q

Axons of sensory neurons

A

Enter limb bud after motor axons, supply dermatomes, which are areas of skin innervated by a single spinal nerve and its dorsal root ganglion

58
Q

Weeks 4-5

A

Most susceptible to teratogen induced limb malformations

59
Q

Three categories of human limb defects

A

Reduction defects, duplication defects, and dysplasia

60
Q

Reduction defect definition

A

Part of (meromelia) or entire limb (amelia) is missing, phocomelia is a type where hands of feet project directly from shoulder or hip

61
Q

Reduction defect example

A

Thalidomide (a teratogen) causes meromelia (at 5 weeks) and amelia (at 4 weeks)

62
Q

Critical period of limb development

A

24-36 days

63
Q

Reduction defect thalidomide mechanism

A

Disruption of the AER

64
Q

Duplication defect definition

A

Extra limb elements are present (polydactyly)

65
Q

Duplication defect mechanism

A

Duplication of the ZPA

66
Q

Dysplasia definition

A

Malformation of part of the limb (syndactyly)

67
Q

Dysplasia mechanism

A

AER doesn’t break down between digits, so apoptosis doesn’t occur normally when forming digits

68
Q

Syndactyly

A

Abnormal fusion of digits due to reduced apoptosis

MSCT (28 decks)

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