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fpp_mss > Musculoskeletal Development - Bolender > Flashcards

Musculoskeletal Development - Bolender Flashcards

1
Q

Recall the precursors for each of the following muscle types:

Smooth

Cardiac

Skeletal

A

Splanchnic mesoderm & local mesenchyme

Splanchnic mesoderm

Paraxial mesoderm

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2
Q

What structure is formed from the paraxial mesoderm late in the third week of development?

A

Somites

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3
Q

Describe the structure of the somite. What does it form?

A

As somites form, they divide into epithelium and mesoderm. Each mesoderm will differentiate into the muscle, bones, cartilage, tendons and skin that comprise the dermatomyotome.

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4
Q

Describe the division of the somite. What forms what?

A

Primaxial muscle domain forms skull & ribs (“scleratome-derived bones”) while abaxial domain forms the muscles of the abdominal wall and limbs.

Note: Epaxial/Hypaxial division falls within the abaxial domain (dermomyotome)

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5
Q

Describe some of the factors involved in myofiber differentiation.

A

“Myogenic regulatory factors (MyoD, MrfH, Myf-5, and Myogenin) are essential for development of muscles.”

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6
Q

How do skeletal muscles become innervated?

A

They are innervated as pre-muscle masses, the take their innervations with them (think of the diaphragm & phrenic nerves)

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7
Q

What are the four myotomes that are superior to the cervical vertebrae?

A

4 occipital myotomes

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8
Q

Are the epaxial muscles innervated by the dorsal or primary rami?

Hypaxial muscles?

A

Epaxial muscles (eg most primaxial muscles) are innervated by the dorsal rami.

Hypaxial muscles are innervated by the ventral primary rami (all abaxial, some primaxial muscles).

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9
Q

At what point in development are muscles “fully” formed & positioned?

A

Week 8

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10
Q

Describe how abnormal development can affect skeletal muscle characteristics.

What is “poland syndrome”?

A

Some variation is normal. Muscles can be fully or partially absent. Dystrophies.

Unilateral abscence of the pectoralis (and webbing of the fingers)

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11
Q

What is “prune-belly syndrome”?

What is a congenital torticollis?

A

Prune-belly syndrome results from malformation of the abdominal muscles (abaxial domain).

Congenital torticollis is a loss of one SCM muscle (head has a charateristic tilt).

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12
Q

What must myoblasts do to complete their maturation process?

A

Th/ey must fuse into multinucleate myotubes.

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13
Q

What is the precursor for bone?

From what is it derived in the trunk and head?

A

Mesenchyme (hence osteosarcoma)

Trunk: Mesenchyme from paraxial/somatic mesoderm.

Head: Mesenchyme from NC ectomesenchyme, head mesoderm.

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14
Q

What factors influence the condensation of STFM into pre-skeletal condensations?

A

Transcription factor and growth factor gradients. Epithelial mesenchymal interactions.

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15
Q

What are the significances of CBFA1 or Sox9?

A

CBFA1 (Runx2) is for osteoblast formation.

Sox9 is a chondroblast-specific transcription factor.

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16
Q

Outline the pathways by which cartilage and bones are formed from STFM.

A

Cartilage: Sox9 activation.

Bone: Runx2 activation (intramembranous), or Runx2 preceded by Sox9 to form cartilage, and then lhh & Vegf (endochondral).

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17
Q

Distinguish between primary and secondary ossification centers.

A

Primary: Initial, first appearing at 7weeks (eg long bone shaft, center of flat bone). One or more in bones.

Secondary: Perinatal/postnatal/postpubertal. Epiphyseal/end of ribs, controlled by hormones (close in 20s-30s).

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18
Q

What is the defect in Marfan’s syndrome? What are the consequences on skeletal development?

A

Fibrillin mutation, leading to arachnodactyly, long limbs, etc.

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19
Q

What is the defect in mucopolysaccharidoses? What are the consequences on skeletal development?

A

Many possible defects of lysosome leading to impaired GAG breakdown. Skeletal dysplasia can result.

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20
Q

What are the consequences of too much growth hormone before puberty? Too little?

Bonus: What are the consequences of too much or little AFTER puberty?

A

Before: Too much = Gigantism. Too little = Pituitary infantilism (dwarfism)

After: Too much = acromegaly, Too little = ???

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21
Q

What is cretinism?

A

Decreased thyroid hormone in development leading to physical and mental stunting.

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22
Q

What is the defect in achondroplasia?

Why does this impair bony development?

A

An autosomal dominant (but usually sporadic) mutation in FGFR3.

No cartilage = no endochondral ossification = dwarfism (most common type!)

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23
Q

Diagnose the following cases:

9y/o boy with angular deformity of a healed fracture; x-ray reveals heavily thickened bone.

5/yo boy with multiple fractures and blue sclerae.

A

Osteopetrosis (X-ray is a giveaway…)

Osteogenesis imperfecta (blue sclerae due to visibility of choroidal veins)

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24
Q

What specifies for the division of the somite into epaxial/hypaxial divisions? (or was it abaxial/primaxial)

A

Growth factor gradients from the notochord & neural tube (eg Shh)

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25
Q

What is a sclerotome?

A

A sclerotome is a portion of a somite which forms the vertebra and ribs.

(somites split into sclerotomes and dermatomyoblasts)

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26
Q

Why is every vertebra the result of fusion of two different sclerotomes?

A

Each scleratome organizes into cranial and caudal subdivisions, these become divided by spinal nerves and each fuses with the scleratome above or below.

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27
Q

Describe the subdomains of scleratomes and what they form.

A

Central: Pedicle & Proximal rib

Ventral: Vertebral body & IV disc

Dorsal: Neural arch & spine

Lateral: Distal rib

Somitocoel cells: Vertebral joint/IV disc, Proximal rib

28
Q

Does the neural arch arise mostly from the cranial or caudal half of the scleratome? The rib?

A

Both arise mostly from the caudal half.

29
Q

Describe how different vertebra develop different morphologies.

A

Axial patterning along the cranial-caudal axis is facilitated by growth factor gradients (eg retinoic acid, hox genes).

30
Q

What is the neurocentral junction? When does it close?

A

It is a cartilaginous growth plate (primary ossification center) in the vertebra. It closes at 3-6yrs.

31
Q

What is Klippel-Feil syndrome?

A

A failure of spinal development where any of the cervical vertebrae become fused.

32
Q

What is the consequence is the two neural arches fail to fuse?

A

Dysraphisms (open vertebral columns), eg Rachiscisis or Spina bifida.

33
Q

Distinguish between a hemivertebra and a block vertebra.

Which are “worse”?

A

Hemivertebrae are incomplete and wedge shaped, introducing flexures into the spine. Block vertebrae are fusions of vertebrae through the IV discs.

Hemivertebrae are more likely to cause neurological problems because of the angulation.

34
Q

A patient has an abnormal spinal flexure such as to give the impression that he is humpbacked. What is this conditon called?

A

Kyphosis (Lordosis is the reverse).

35
Q

Summarize how the ribs and sternum form.

A

Ribs are extensions of the costal processes that develop adjacent to the neural arches. The sternum results from the fusion of sternal bands, followed by ossification.

36
Q

Describe some abnormalities of rib or sternal development.

A

Accessory ribs can form, or they may be forked/fused.

The sternum may be cleft (Pectus Excavatum or Carinatum)

37
Q

What precursor tissues contribute to limb development?

A

Surface ectoderm and “limb mesenchyme” (somatic/somitic mesoderm).

38
Q

Which develops sooner: the upper limb or lower limb?

A

Upper limb development precedes lower limb by 1-2 days.

39
Q

What is the very first step in limb development?

A

Establishment of a bilateral limb field.

40
Q

As the limb buds, what is present at its tip?

What drives budding?

A

The apical ectodermal ridge, a thickening of ectoderm.

Budding is driven by mesoderm, not ectoderm. This is facilitated by interactions between the two at the AER/mesoderm surface.

41
Q

Limb tissue differentiation and organization occur during weeks 5-9 of development. In what direction does it proceed?

A

Proximal-to-distal.

42
Q

Define the three developmental axes in limbs.

A

Proximal-distal (important for elongation of the limb)

Anterior-posterior (eg radial-ulnar)

Dorsal-ventral (eg volar-dorsal, or flexor-extensor compartments)

43
Q

What signaling factors are present at the proximal and distal poles in limb development?

A

Proximal: Retinoic acid

Distal: Fgf, Wnt

44
Q

Which tissue controls upper vs lower limb determination?

Which tissue maintains the 3 axes?

A

Mesenchyme determines limb type.

AER maintains axes via signaling centers or protein gradients.

45
Q

The mesenchyme that is adjacent to the AER is called the “progress zone”. What is its developmental fate?

A

To form skeletal and connective tissue elements…?

46
Q

What are the consequences of the following:

AER removal

AER duplication

Translocation of AER to truncal mesenchyme

A

Removal results in truncation (Amelia/Meromelia)

Duplication will cause limb duplication (eg syndactyly)

Translocation will cause a new, ectopic limb to grow.

47
Q

What is the significance of the zone of polarizing activity?

What are the consequences of its duplication?

A

The ZPA is an organization center located along the posterior border of the limb. It helps define the A-P axis via signaling factors Shh and retinoic acid.

Duplicating it will cause loss of A-P differentiation (eg mirror imaging)

48
Q

Hemimelia is a failure along which limb developmental axis?

Amelia is a failure along which limb developmental axis?

What is phocomelia?

A

Hemimelia results from failure along the A-P axis.

Amelia results from failure along the P-D axis.

Phocomelia is characterized by limb attachment close to the body (shoulder, pelvic dysplasia). Classically seen with thalidomide, it also has some genetic causes.

49
Q

Name 2-3 conditions that can result from failure of apoptosis in limb development.

A

Sirenomelia (legs fail to separate, “mermaid”-like)

Syndactyly (webbing between fingers)

Triphalangeal thumb (third phalanx normally ablates)

50
Q

What factors mediate dorsal-ventral patterning?

A

Secreted factors (eg Wnt 7a)

Engrailed (En) transcription factor

51
Q

Try to summarize the 7 forms of abnormal limb development.

A
  1. Failure of formation
  2. Failure of separation (apoptosis)
  3. Duplication
  4. Overgrowth
  5. Undergrowth
  6. Amniotic constriction banding
  7. Generalized skeletal abnormalities
52
Q

What are some consequences of hip developmental dysplasia?

A

Increased joint laxity. Dislocations?

53
Q

What is a sprengel deformity?

A patient can abduct her arms such that her two humerus bones touch under her chin. What part of the upper limb girdle is affected?

A

Failure of descent of one shoulder–the scapulas are uneven

“Cleidocranial dysplasia”, no clavicles!

54
Q

What is Talipes Equinvarus?

A

AKA Club foot. Deformity involving internal ankle rotation. If untreated, patients would walk on their ankles and lateral foot surfaces.

55
Q

What ultimately happens to the AER?

Where do limb muscles originate from, again?

A

As limb maturation completes, it probably forms dermis & connective tissue distally.

Condensations of mesoderm from somites.

56
Q

Folic Acid Deficiency

What are the consequences?

What are some risk factors?

How much is recommended?

A

Folic Acid Deficiency

Needed for cell differentiation (single-carbon transfers). Deficiency during pregnancy will result in CNS malformations eg spina bifida and anencephaly.

Gluten-free diets (grains & legumes provide B-vitamins)

400mcg for women of childbearing age, 600mcg for pregnancy.

57
Q

Why is cod liver oil contraindicated in pregnant women?

A

Cod liver oil contains retinol (animal form of vitamin A), which is teratogenic*. Replace it with plant sources (beta-carotene)

*This seems controversial.

58
Q

What is the fetal-origins hypothesis of chronic disease risk?

A

Nutritional conditions in the womb can “program” the fetus in a way as to increase risk for certain chronic illnesses.

(google “thrifty phenotype”)

59
Q

Why is a modern, breastfed baby at potential risk of vitamin D deficiency?

How should vitamin D levels be tested?

A

Breastmilk does not contain adequate vitamin D. Modern babies are presumably slathered in sunblock which can stop vitamin D activation in the skin.

Test for 25-OH D3 (calcifediol) in blood.

60
Q

What are the symptoms of essential fatty acid deficiency?

A

Compromised wound healing, slowed growth, and dry scaly skin, occurring after 2-10/10-20 days (infants/adults) without fat.

Humans require >3% fat-derived calories.

61
Q

What are some risk factors involved in calcium deficiency?

A

Being african american or hispanic.

Avoidance of dairy products.

High grain/iron diets.

Being a teenager, apparently.

62
Q

definitions:

  1. DRI
  2. EAR
  3. RDA
  4. AI
  5. UL
A
  1. Dietary reference intake
  2. Estimated Average Requirement - average nutrient intake estimated to meet requirements of 50% of healthy individuals in a group
  3. Recommended dietary allowances - average nutrient intake estimated to meet reuqirements of nearly all (97-98%) healthy individuals in a group
  4. Adequate intake - mean intake needed to cover all healthy individuals in a group
  5. Tolerable upper intake level - highest level to pose no risk of adverse health effects in all individuals
63
Q

Recall 3 different types of joints.

A

Fibrous (eg lumbosacral)

Cartilaginous (eg IV discs)

Synovial (eg elbow)

64
Q

What factors specify for joint development? How is this accomplished?

A

The space between bones is rich in Wnt9a and Noggin, which inhibit BMPs.

65
Q

What is the consequence of a joint is not allowed to move during prenatal development?

A

A normal joint will not form; the joint becomes immobile/fixed.

66
Q

What is the interzone? Is it present in every immature joint?

A

Interzone is an area between the cartilage caps of bones, in which Wnt9a is expressed. Some joints (eg interphalangeals) do not feature interzones.

fpp_mss (30 decks)

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