ANATOMY (Development of MSK System) Flashcards
Musculoskeletal system (MSK) consists of:
-bones
-cartilage
-muscles
-ligaments
-tendons
Main functions of MSK:
-support the body
-provision of motion
-protection of vital organs (brain, viscera)
-main storage system for calcium and phosphorus
Early germ layer derivatives:
-particular pole of the blastocyst differentiates into embryonic disc (epiblast)
>beginning of gastrulation
3 germ layers:
-ectoderm: epiblast, blue, ex. skin
-mesoderm: cells that enter, orange/red, ex. muscle
-endoderm: cells on bottom, yellow, ex. GI system
Somitogenesis:
-development of somites
-each somite differentiates into three components
>scleratome
>dermamyotome
Scleratome:
-part of each somite in a vertebrate embryo giving rise to bone or other skeletal tissues
-‘loose cells’
Dermamyotome:
-dermatome
-myotome
Neural crest cells:
-in cross-sections of the fusing neural folds into the neural tube
-cells at the crest of the folds begin to detach
Osteogenesis requires mesenchyme:
-derived from various parts
>scleratomal part of somites
>lateral plate
>ectodermal neural crest
Mesenchyme:
-star shaped cells that form the bulk of interstitial
-‘glue’
-surrounds the cells and helps anchor them
-can develop into a variety of cells
Scleratomal part of somites (mesenchyme):
-gives rise to segmented axial column
>vertebral column
>ribs
>sternum
Lateral plate (mesenchyme):
-gives rise to appendicular skeleton
>limbs and respective girdles
Ectodermal neural crest (mesenchyme):
-gives rise to facial bones and bones that cover the brain
Gross observation of bone:
-compact bone
-cancellous or spongy bone
*both have same histological components
*both have two types of organization
Compact bone:
-dense areas without cavities
-80% of bone mass
Cancellous or spongy bone:
-areas of bone (struts or rods) with interconnecting cavities
-20% of bone mass
2 types of bong organization:
-during development: woven bone
-in adults: lamellar bone
During development: bone organization
-primarily, immature or woven bone
-randomly arranged matrix components (ex. cells, collagen)
In adults: bone organization
-secondary, mature or lamellar bone is present
-discrete sheets or layers of matrix
Intramembranous or desmal ossification:
-direct conversion of mesenchymal cells into bone
Ex. blastema
Blastema example:
-skull neural-crest derived mesenchymal cells divide and then coalesce into compact groups or aggregates
Osteoblast formation:
-some mesenchymal cells develop into osteoblasts
Osteoblast function:
-secrete osteoid
-become osteocytes
Osteoid:
-an extracellular matrix of collagen and proteoglycan that bind calcium
>become calcified
Osteocytes:
-when osteoblasts are surrounded by calcified osteoid
Periosteum:
-formed by compact layers of mesenchymal cells
-a membrane of cells that surround bone
Developing bone becomes:
-vascularized
-collagen fibers disorganized
-periosteum surrounding both sides
-many osteocytes
*woven bone
>will then get reorganized on outer edges
Endochondral bone formation:
-involves mesenchymal cells first differentiating into cartilage then later replacing it with bone
Ex. long bones
Endochondral bone found in:
-vertebral column
-ribs
-pelvis
-limbs
Long bone formation:
- Cartilage model or framework
- Matrix begins to calcify
- Periosteal/osteogenic bud
- Secondary ossification centre
- Cartilage continues in two regions (in epiphyses)
Cartilage model or framework
-formed and then the bone collar develops in local perichondrium (via local intramembranous bone formation)
Bone collar:
-hollow bone cylinder
-periosteum
Matrix begins to calcify:
-in middle of cartilage framework (diaphysis), chondrocytes hypertrophy
>begin to produce matrix, degenerate and matrix begins to calcify
Periosteal/osteogenic bud:
-capillaries
-osteoprogenitor cells (form osteoblasts)
-mesenchymal cells
*invades they hypertrophied cartilage
>bud grows and lays down compact bone in shaft=primary ossification center is produced
Secondary ossification centre:
-develops at each end of the cartilage framework called epiphysis
Cartilage continues in two regions:
-articular cartilage
-epiphyseal cartilage
Vertebral column:
-notochord
-vertebrae
Notochord:
-induces surrounding mesenchyme to secrete epimorphin
-coalesce and differentiate into cartilage
Epimorphin:
-secreted from mesenchyme
-a chemoattractant for scleratomal cells to move around notochord and neural tube
Scleratome cells form vertebra:
-split into populations
>loosely packed cranial segment
>densely packed caudal segment
Vertebral development:
-occurs through process of re-segmentation
Re-segmentation:
-caudal half of one sclerotome joins with cranial half of the next to form the centrum or body of vertebrae
-enables motor neurons to grow out laterally and innervate newly forming muscles form myotome
Vertebral ossification:
-endochondral ossification
>from centres of the vertebral body and arches
Ribs:
-arise from segmental sclerotome-derived mesenchymal condensations beside thoracic vertebrae
3D coordinate system of the limb:
-need positional information to construct the limb
>proximal-distal
>anterior-posterior
>dorsal-ventral
Limb field:
-all cells in an area that can form a limb on their own
Limb development starts when:
-mesenchyme cells migrate from the limb fields in the:
>lateral plate mesoderm (limb skeletal precursors)
>somites (limb muscle precursors)
Limb extends due to:
-signalling in AER
>*gradients of retinoic acid and FGFs occur
FGFs:
-fibroblast growth factors
Gradients of retinoic acid and FGFs:
-stimulate the regional expression of Hox genes and the patern of the limb
>stylopod
>zeugopod
>autopod
Stylopod:
-humerus/femur
Zeugopod:
-radius/ulna
-tibia/fibula
Autopod:
-carpals/fingers
-tarsals/toes
Dermatome:
-forms dermis of skin
Myotome:
-will produce precursor myoblast cells that will give rise to Epaxial and Hypaxial muscles
Epaxial muscles:
-intercostal
-deep muscles of back
Hypaxial muscles:
-body wall
-limbs
-tongue
Canals within cartilage:
-form from the perichondrium around the region
>contain venules, arterioles and nerve fibers
*osteogenic cells supplied
Cartilage canals from the perichondrium:
-supply the osteogenic cells to the area
*long bone epiphyseal cartilage
*prepubertal period
Epiphyseal cartilage: prepubertal period 5 zones
- Resting zone
- Proliferative zone
- Hypertrophic zone
- Resorption zone
- Ossification zone
Resting zone:
-non-proliferative chondrocytes
-stem cell population
Proliferative zone:
-stacked columns of chondrocytes that divide
Hypertrophic zone:
-containing large chondrocytes
Resorption zone:
-dying chondrocytes
-resorption/calcification of cartilage matrix
Ossification zone:
-new bone tissue formed by osteoblasts
>produce osteoid over remnants of calcified cartilaginous matrix which will become ossified
Adult bones:
-Haversian canal
-osteon
-Volkmann’s canals
-lacunae with canaliculi
Haversian canal:
-collagen fibres in parallel or concentrically around vascular canal
>interstitial lamellae
Osteon:
-whole complex of lamellae with canal contain blood vessels and nerves
Volkmann’s canals:
-connect Haversian canals
Lacunae with canaliculi:
-between lamellae
-connect to Haversian canal
>nutrition and communication
*contain osteocytes
Lacunae with osteocytes:
-want to keep osteocytes as near to capillaries as possible
Cortical compact bone remodelling
- Starts at leading edge (cutting edge)
- Reversal zone
- Closing zone
Cutting edge:
-where cortical compact bone remodelling starts
-where the osteoclasts break down existing bone
Reversal zone:
-switch from resorption to formation of new bone begins involving osteoblasts
Closing zone:
-where osteoblasts build new lamellae
Spongy bone remodelling:
-osteoclasts work on endosteal surface to break down matrix
-osteoblasts form endosteal surface then add more bone on same or opposite regions
Fracture leads to:
-blood clots
-osteocytes die on each side of fracture
Fracture repair:
-callus needs to form
-osteogenic cells
-new osteons laid down
-original structure restored
Callus needs to form:
-periosteal and endosteal cells
-internal and external callus
Internal callus:
-between opposing sides of fracture
External callus:
-around outer broken surface if ends move (other only internal callus)
Osteogenic cells near blood supply (fracture repair):
-form bone directly
Osteogenic cells away from blood supply (fracture repair):
-form cartilage first, then remodel to bone
*osteogenic cells/capillaries from living bone can invade any dead bone with help of osteoclasts
