Embryology of Musculoskeletal System ✅ Flashcards

1
Q

What does development of the MSK system require?

A

Differentiation into specific cell types, and co-ordination to produce an integrated and functional system

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2
Q

What does the MSK system develop from?

A

Mainly the mesodermal germ layer, with some neural crest contribution

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3
Q

What is mesoderm subdivided into?

A
  • Paraxial
  • Intermediate
  • Lateral
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4
Q

What happens to the mesoderm in the 3rd week of gestation?

A

The paraxial mesoderm forms ‘little balls’ (somites), which are paired each side of the neural groove

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5
Q

What happens to the somites?

A

They differentiate differently in different regions

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6
Q

What can the somites differentiate into?

A
  • Sclerotome

- Dermomyotome

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7
Q

What happens to the sclerotome in development?

A

It splits segmentally, giving rise to the vertebral column

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8
Q

What does the dermomyotome develop into?

A

Dermal and muscle components

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9
Q

What creates the limb buds?

A

The migration of the lateral mesoderm and the dermomyotome to the limb field

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10
Q

What gives rise to the mesenchyme?

A

Mesodermal cells

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11
Q

What is the mesenchyme?

A

Loosely organised connective tissue

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12
Q

What do mesenchymal cells differentiate into?

A

They are pluripotent, and differentiate into many different cell types, including bones and cartilage

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13
Q

What are the ways that bones can develop?

A
  • Direct ossification of the mesenchyme

- Endochondrial ossification

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14
Q

What bones form from direct ossification of the mesenchyme?

A
  • Cranial bones of the skull

- Clavicle

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15
Q

What bones form from endochondrial ossification?

A

The bones of the limb and girdle

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16
Q

What is endochondrial ossification?

A

The ossification of a cartilaginous precursor of the long bones of the skeleton

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17
Q

What is the first step in endochondrial ossification?

A

Condensation of lateral plate mesenchyme occurring in a rod-like structure along the axis of the limb bud

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18
Q

What happens after the condensation of lateral plate mesenchyme in the limb buds?

A

Chondrocytes (cartilage cells) respond to growth factors and differentiate in a process called chondrification.

19
Q

What do the chondrocytes secrete?

A

Proteoglycans and collagen

20
Q

What is the result of the proteoglycan and collagen secretion by chondrocytes?

A

Formation of cartilage

21
Q

Where is there deposition of cartilage initially?

A

Around the entire limb condensations

22
Q

Where does further chondrification occur after the initial deposition of cartilage?

A

Limited to future bone sites, sparing the inter-zone regions

23
Q

What does the sparing of inter-zone region in further chondrification lead to?

A

Site of future joints

24
Q

What is the initial step in the formation of the joints of the long bones?

A

Mesenchymal cells at the interzones of long bones differentiate into multiple fibroblastic connective tissue layers

25
Q

What happens to the fibroblastic connective tissue layers at the interzones of long bones?

A

They differentiate further to provide the articular cartilage at either end of the joint, and connective tissue in the middle forms the internal structures of the joint

26
Q

What internal structures of the joint are produced from connective tissue in the middle of the fibroblastic connective tissue layers?

A
  • Synovial tissue
  • Menisci
  • Ligaments
27
Q

How is the joint cavity formed?

A

Vacuoles form within the connective tissue, which then becomes the joint cavity

28
Q

How is the joint capsule formed?

A

The mesenchymal sheath becomes the joint capsule

29
Q

How are fibrous joints, or immobile joints which connect bones (e.g. skull, pelvis), formed?

A

Also developed from interzones, which differentiate into a single layer of fibrous connective tissue

30
Q

What happens following chondrification?

A

Ossification

31
Q

Where does ossification occur from?

A

The primary ossification centre

32
Q

What happens to mesenchymal cells in the primary ossification centre?

A

They differentiate into bone cells (osteoblasts) in response to growth factors

33
Q

What do the osteoblasts secrete?

A

The calcium matrix of mineralised bone

34
Q

What appears alongside the osteoblasts?

A

Osteoclasts

35
Q

What do osteoclasts do?

A

Reabsorb bone, enabling remodelling of growing bone

36
Q

What does the limb musculature develop from?

A

Two condensations of somitic mesoderm

37
Q

How does the somitic mesoderm form the limb musculature?

A

In the 5th week, the condensations of somitic mesoderm invades the limb bud, one ventrally and one dorsally

38
Q

What does the ventral somatic mesoderm give rise to?

A

Mainly flexors, pro atoms, and adductor muscles

39
Q

What does the dorsal somatic mesoderm give rise to?

A

Mainly extensors, supination, and abductor muscles

40
Q

What do cells in the condensations of somitic mesoderm differentiate into?

A

Myoblasts (muscle cell precursors)

41
Q

What happens to myoblasts?

A

They fuse together to form syncytial

42
Q

How does the inner action of the limb muscles develop?

A

From branches that develop from spinal nerve axons in a multi step process

43
Q

What do branches of the ventral spinal nerve inner age?

A

Ventral muscles

44
Q

What do branches of the dorsal spinal nerve innervate?

A

Dorsal muscles