Musculoskeletal System - Bone Development: Difference between revisions
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==Bone Structure== | |||
=== Terminology === | |||
* '''Diaphysis''' - shaft | |||
* '''Epiphysis''' - expanded ends | |||
* '''Metaphysis''' - connecting region (between diaphysis and epiphysial line) | |||
* '''Medullary Cavity''' - (marrow) cavity within the bone. | |||
===Compact bone=== | |||
* (dense) no spaces or hollows in the bone matrix visible to the eye. | |||
* forms the thick-walled tube of the shaft (or diaphysis) of long bones, which surrounds the marrow cavity (or medullary cavity). A thin layer of compact bone also covers the epiphyses of long bones. | |||
===Trabecular bone=== | |||
* (cancellous or spongy bone) consists of delicate bars (spicules) and sheets of bone, trabeculae | |||
* branch and intersect to form a sponge-like network | |||
* ends of long bones (or epiphyses) consist mainly of trabecular bone. | |||
===Periosteum=== | |||
Connective tissue covering the surface of bone (except articular surfaces). | |||
[[File:Periosteum.jpg]] | |||
===Endosteum=== | |||
Connective tissue lining inner surface of bone. | |||
===Bone Growth=== | |||
* Appositional growth occurs at either the periosteum (outer surface), or the endosteum (inner surface). | |||
* Osteoblasts secrete '''osteoid''', a pre-bone material composed mainly of type I collagen that becomes mineralized. | |||
* Early bone matrix deposited in development and during repair is '''woven''' rather than '''lamellar''' in appearance and structure. | |||
* In development, there are 2 distinct types of bone formation (intramembranous and endochondral) | |||
== Bone Cells == | |||
===Osteoblasts=== | |||
* derive from osteogenic stem cells the '''osteoprogenitor cells''' that differentiate to form pre-osteoblast then '''osteoblasts''' maturing to an osteocyte | |||
* osteoprogenitor cells - "resting cell" line the inner and outer surfaces of bone | |||
===Osteocytes=== | |||
* mature bone-forming cells embedded in '''lacunae''' within the bone matrix | |||
* osteoblasts and osteocytes - secrete organic matrix of bone (osteoid), converted into '''osteocytes''' when become embedded in matrix (which calcifies soon after deposition) | |||
===Osteoclasts=== | |||
[[File:Osteoclast.jpg]] [[File:Bone_remodeling_cycle.jpg|400px]] | |||
* bone-resorbing multinucleated macrophage-like cells | |||
* origin- fusion of monocytes or macrophages, Blood macrophage precursor, Attach to bone matrix | |||
* seal a small segment of extracellular space (between plasma membrane and bone surface), HCl and lysosomes secreted into this space by osteoclasts dissolves calcium phosphate crystals (give bone rigidity and strength) | |||
** Resorptive bay - (Howship's lacuna) shallow bay lying directly under an osteoclast. | |||
* do not mistake for megakaryocytes, found in bone marrow not associated with bone matrix. | |||
** megakaryocytes are also multi-niucleated and form platelets | |||
===Bone Marrow=== | |||
[[File:Hematopoietic and stromal cell differentiation.jpg|thumb|Hematopoietic and stromal cell differentiation]] | |||
* '''red marrow''' - mainly haematopoietic (myeloid) tissue, newborn has all red marrow | |||
* '''yellow marrow''' - mainly fat cells, found in diaphysis region of long bones | |||
* '''stromal cells''' - all other support cells not involved in haematopoiesis | |||
==Chondroblasts and Chondrocytes== | |||
<gallery> | |||
File:Articular cartilage.jpg|Articular cartilage | |||
File:Gray0299.jpg|Synovial joint showing cartilage | |||
</gallery> | |||
* immature and mature cartilage forming cells located at articular cartilage regions. | |||
* '''Interstitial growth''' - occurs mainly in immature cartilage. Chondroblasts in existing cartilage divide and form small groups of cells (isogenous groups) which produce matrix to become separated from each other by a thin partition of matrix. | |||
* '''Appositional growth''' - occurs also in mature cartilage. Mesenchymal cells surrounding the cartilage in the deep part of the perichondrium (or the chondrogenic layer) differentiate into chondroblasts. | |||
[http://www.lab.anhb.uwa.edu.au/mb140/CorePages/Cartilage/Cartil.htm Histology - Cartilage] | |||
== Bone Matrix == | |||
The bone matrix has 2 major components. | |||
* '''Organic portion''' composed of mainly collagen Type 1 (about 95%) and amorphous ground substance. | |||
* '''Inorganic portion''' (50% dry weight of the matrix) composed of hydroxyapatite crystals, calcium, phosphorus, bicarbonate, nitrate, Mg, K, Na. | |||
** storage calcium and phosphate | |||
** regulate blood calcium levels | |||
==Haversian Systems== | |||
[[File:Bone structure cartoon.jpg|thumb|Bone structure cartoon]] | |||
* also called osteons | |||
* Volkmann's canals - interconnect Haversian systems | |||
===Lamellae=== | |||
* concentric - surrounding each Haversian System | |||
* interstitial - bony plates that fill in between the haversian systems. | |||
* circumferential - layers of bone that underlie the periosteum and endosteum | |||
===Cells=== | |||
* osteocytes extending cytoplasmic processes into canaliculi | |||
* Additional Histology images: [http://embryology.med.unsw.edu.au/pdf/histoimages/10ax10.pdf low] | [http://embryology.med.unsw.edu.au/pdf/histoimages/10ax20.pdf medium] | [http://embryology.med.unsw.edu.au/pdf/histoimages/10ax40.pdf high] | |||
==Endochondral ossification== | |||
[[File:Endochondral_bone.jpg|thumb]] | |||
'''Endochondral ossification slides:''' [http://vslide1.med.unsw.edu.au/slide.jsp?fn=histology/b12_40xr.fpx&mag=40 Developing bone] | [http://vslide1.med.unsw.edu.au/slide.jsp?fn=anatomy/ANAT6778.svs&mag=40 Bone, Developing (LS, Femur) Cat H&E] | |||
[http://www.lab.anhb.uwa.edu.au/mb140/CorePages/Bone/Bone.htm#endochondral Blue Histology - endochondral] | [http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=dbio&part=A3479&rendertype=figure&id=A3484 Dev Biology - endochondral ossification] | [http://commons.bcit.ca/biology/ossification/files/ossification2.html endochondral ossification animation] | |||
[[File:Endochondral ossification.jpg]] [[File:Endochondral ossification 2.jpg]] | |||
[[File:Ossification_endochondral_1c.jpg|link=File:Ossification_endochondral_1.jpg]] [[File:Articular cartilage.jpg]] | |||
Additional Histology Slides: [http://embryology.med.unsw.edu.au/pdf/histoimages/9x5.pdf developing Vertebra] | [http://embryology.med.unsw.edu.au/pdf/histoimages/9x10n3.pdf Vertebra medium] | |||
==Intramembranous ossification== | |||
'''Intramembranous ossification slides:''' [http://vslide1.med.unsw.edu.au/slide.jsp?fn=anatomy/ANAT893.svs&mag=40&mag=40 Head (Neonatal) Rat H& Van Gieson] | |||
[http://www.lab.anhb.uwa.edu.au/mb140/CorePages/Bone/Bone.htm#intramembranous Blue histology - intramembranous] | [http://commons.bcit.ca/biology/ossification/files/ossification1.html intramembranous ossification animation] | |||
[[File:Ossification_centre.jpg]] [[File:Intramembranous_ossification_centre.jpg]] | |||
===Human Fetal Head (12 week)=== | |||
[[File:Fetal head medial.jpg|300px]] [[File:Fetal head lateral.jpg|300px]] | |||
[[File:Meckel.jpg|600px]] | |||
[[File:Fetal_head_section.jpg|600px]] | |||
==Molecular== | ==Molecular== |
Revision as of 14:12, 18 December 2010
Introduction
The mesoderm forms nearly all the connective tissues of the musculoskeletal system. Each tissue (cartilage, bone, and muscle) goes through many different mechanisms of differentiation.
The musculoskeletal system consists of skeletal muscle, bone, and cartilage and is mainly mesoderm in origin with some neural crest contribution.
The intraembryonic mesoderm can be broken into paraxial, intermediate and lateral mesoderm relative to its midline position. During the 3rd week the paraxial mesoderm forms into "balls" of mesoderm paired either side of the neural groove, called somites.
Somites appear bilaterally as pairs at the same time and form earliest at the cranial (rostral,brain) end of the neural groove and add sequentially at the caudal end. This addition occurs so regularly that embryos are staged according to the number of somites that are present. Different regions of the somite differentiate into dermomyotome (dermal and muscle component) and sclerotome (forms vertebral column). An example of a specialized musculoskeletal structure can be seen in the development of the limbs.
Skeletal muscle forms by fusion of mononucleated myoblasts to form mutinucleated myotubes. Bone is formed through a lengthy process involving ossification of a cartilage formed from mesenchyme. Two main forms of ossification occur in different bones, intramembranous (eg skull) and endochondrial (eg limb long bones) ossification. Ossification continues postnatally, through puberty until mid 20s. Early ossification occurs at the ends of long bones.
Musculoskeletal and limb abnormalities are one of the largest groups of congenital abnormalities.
Some Recent Findings
Adult Human Skeleton
Textbooks
- The Developing Human: Clinically Oriented Embryology (8th Edition) by Keith L. Moore and T.V.N Persaud - Moore & Persaud Chapter 15 the skeletal system
- Larsen’s Human Embryology by GC. Schoenwolf, SB. Bleyl, PR. Brauer and PH. Francis-West - Chapter 11 Limb Dev (bone not well covered in this textbook)
- Before we Are Born (5th ed.) Moore and Persaud Chapter 16,17: p379-397, 399-405
- Essentials of Human Embryology Larson Chapter 11 p207-228
Objectives
- Identify the components of a somite and the adult derivatives of each component.
- Give examples of sites of (a) endochondral and (b) intramembranous ossification and to compare these two processes.
- Identify the general times (a) of formation of primary and (b) of formation of secondary ossification centres, and (c) of fusion of such centres with each other.
- Briefly summarise the development of the limbs.
- Describe the developmental abnormalities responsible for the following malformations: selected growth plate disorders; congenital dislocation of the hip; scoliosis; arthrogryposis; and limb reduction deformities.
Development Overview
Below is a very brief overview using simple figures of 3 aspects of early musculoskeletal development. More detailed overviews are shown on other notes pages Mesoderm and Somite, Vertebral Column, Limb in combination with serial sections and Carnegie images.
Mesoderm Development
Cells migrate through the primitive streak to form mesodermal layer. Extraembryonic mesoderm lies adjacent to the trilaminar embryo totally enclosing the amnion, yolk sac and forming the connecting stalk. | |
Paraxial mesoderm accumulates under the neural plate with thinner mesoderm laterally. This forms 2 thickened streaks running the length of the embryonic disc along the rostrocaudal axis. In humans, during the 3rd week, this mesoderm begins to segment. The neural plate folds to form a neural groove and folds. | |
Segmentation of the paraxial mesoderm into somites continues caudally at 1 somite/90minutes and a cavity (intraembryonic coelom) forms in the lateral plate mesoderm separating somatic and splanchnic mesoderm.
Note intraembryonic coelomic cavity communicates with extraembryonic coelom through portals (holes) initially on lateral margin of embryonic disc. | |
Somites continue to form. The neural groove fuses dorsally to form a tube at the level of the 4th somite and "zips up cranially and caudally and the neural crest migrates into the mesoderm. |
Somite Development
Mesoderm beside the notochord (axial mesoderm, blue) thickens, forming the paraxial mesoderm as a pair of strips along the rostro-caudal axis. | |
Paraxial mesoderm towards the rostral end, begins to segment forming the first somite. Somites are then sequentially added caudally. The somitocoel, is a cavity forming in early somites, which is lost as the somite matures. | |
Cells in the somite differentiate medially to form the sclerotome (forms vertebral column) and dorsolaterally to form the dermomyotome. | |
The dermomyotome then forms the dermotome (forms dermis) and myotome (forms muscle).
Neural crest cells migrate beside and through somite. | |
The myotome differentiates to form 2 components dorsally the epimere and ventrally the hypomere, which in turn form epaxial and hypaxial muscles respectively. The bulk of the trunk and limb muscle coming from the Hypaxial mesoderm. Different structures will be contributed depending upon the somite level. |
Limb Development
Bone Structure
Terminology
- Diaphysis - shaft
- Epiphysis - expanded ends
- Metaphysis - connecting region (between diaphysis and epiphysial line)
- Medullary Cavity - (marrow) cavity within the bone.
Compact bone
- (dense) no spaces or hollows in the bone matrix visible to the eye.
- forms the thick-walled tube of the shaft (or diaphysis) of long bones, which surrounds the marrow cavity (or medullary cavity). A thin layer of compact bone also covers the epiphyses of long bones.
Trabecular bone
- (cancellous or spongy bone) consists of delicate bars (spicules) and sheets of bone, trabeculae
- branch and intersect to form a sponge-like network
- ends of long bones (or epiphyses) consist mainly of trabecular bone.
Periosteum
Connective tissue covering the surface of bone (except articular surfaces).
Endosteum
Connective tissue lining inner surface of bone.
Bone Growth
- Appositional growth occurs at either the periosteum (outer surface), or the endosteum (inner surface).
- Osteoblasts secrete osteoid, a pre-bone material composed mainly of type I collagen that becomes mineralized.
- Early bone matrix deposited in development and during repair is woven rather than lamellar in appearance and structure.
- In development, there are 2 distinct types of bone formation (intramembranous and endochondral)
Bone Cells
Osteoblasts
- derive from osteogenic stem cells the osteoprogenitor cells that differentiate to form pre-osteoblast then osteoblasts maturing to an osteocyte
- osteoprogenitor cells - "resting cell" line the inner and outer surfaces of bone
Osteocytes
- mature bone-forming cells embedded in lacunae within the bone matrix
- osteoblasts and osteocytes - secrete organic matrix of bone (osteoid), converted into osteocytes when become embedded in matrix (which calcifies soon after deposition)
Osteoclasts
- bone-resorbing multinucleated macrophage-like cells
- origin- fusion of monocytes or macrophages, Blood macrophage precursor, Attach to bone matrix
- seal a small segment of extracellular space (between plasma membrane and bone surface), HCl and lysosomes secreted into this space by osteoclasts dissolves calcium phosphate crystals (give bone rigidity and strength)
- Resorptive bay - (Howship's lacuna) shallow bay lying directly under an osteoclast.
- do not mistake for megakaryocytes, found in bone marrow not associated with bone matrix.
- megakaryocytes are also multi-niucleated and form platelets
Bone Marrow
- red marrow - mainly haematopoietic (myeloid) tissue, newborn has all red marrow
- yellow marrow - mainly fat cells, found in diaphysis region of long bones
- stromal cells - all other support cells not involved in haematopoiesis
Chondroblasts and Chondrocytes
- immature and mature cartilage forming cells located at articular cartilage regions.
- Interstitial growth - occurs mainly in immature cartilage. Chondroblasts in existing cartilage divide and form small groups of cells (isogenous groups) which produce matrix to become separated from each other by a thin partition of matrix.
- Appositional growth - occurs also in mature cartilage. Mesenchymal cells surrounding the cartilage in the deep part of the perichondrium (or the chondrogenic layer) differentiate into chondroblasts.
Bone Matrix
The bone matrix has 2 major components.
- Organic portion composed of mainly collagen Type 1 (about 95%) and amorphous ground substance.
- Inorganic portion (50% dry weight of the matrix) composed of hydroxyapatite crystals, calcium, phosphorus, bicarbonate, nitrate, Mg, K, Na.
- storage calcium and phosphate
- regulate blood calcium levels
Haversian Systems
- also called osteons
- Volkmann's canals - interconnect Haversian systems
Lamellae
- concentric - surrounding each Haversian System
- interstitial - bony plates that fill in between the haversian systems.
- circumferential - layers of bone that underlie the periosteum and endosteum
Cells
- osteocytes extending cytoplasmic processes into canaliculi
- Additional Histology images: low | medium | high
Endochondral ossification
Endochondral ossification slides: Developing bone | Bone, Developing (LS, Femur) Cat H&E
Blue Histology - endochondral | Dev Biology - endochondral ossification | endochondral ossification animation
Additional Histology Slides: developing Vertebra | Vertebra medium
Intramembranous ossification
Intramembranous ossification slides: Head (Neonatal) Rat H& Van Gieson
Blue histology - intramembranous | intramembranous ossification animation
Human Fetal Head (12 week)
Molecular
The transcription factors Runx2 and Runx3 are essential for chondrocyte maturation, while Runx2 and Osterix are essential for osteoblast differentiation.
Osterix
Osterix (OSX) encodes a transcription factor containing three Cys2-His2 zinc-finger DNA-binding domains at its C terminus that has been shown to be essential for bone formation.
Abnormalities
Osteogenesis Imperfecta
Osteogenesis Imperfecta (OI, brittle bone disease) originally described as a collagen 1 gene mutation, but can have several different genetic causes and can be classified into eight different types (I-VIII).[1]
- COL1A1 and COL1A2 mutations
- CRTAP and LEPRE1 mutations, in severe/lethal and recessively inherited osteogenesis imperfecta
References
- ↑ <pubmed>19907330</pubmed>
Reviews
<pubmed>19883365</pubmed> <pubmed>17659995</pubmed>
Articles
Search PubMed
Search April 2010
- Musculoskeletal System Development - All (44637) Review (5065) Free Full Text (6601)
- Musculoskeletal Development - All (44637) Review (5065) Free Full Text (6601)
Search Pubmed: Bone Development | developmental ossification | endochondral ossification | intramembranous ossification
Additional Images
Terms
Glossary Links
- Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link
Cite this page: Hill, M.A. (2024, April 23) Embryology Musculoskeletal System - Bone Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Musculoskeletal_System_-_Bone_Development
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G