Musculoskeletal System - Bone Development: Difference between revisions
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==Ossification Centres== | ==Ossification Centres== | ||
[[File:Mouse_limb_cartilage_and_bone_E14.5.jpg|thumb|300px|Mouse limb showing primary ossification.<ref><pubmed>20386744</pubmed>| [http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2851570 PMC2851570] | [http://www.plosgenetics.org/article/info%3Adoi%2F10.1371%2Fjournal.pgen.1000901 PLoS Genet.]</ref>]] | |||
===Primary Ossification=== | ===Primary Ossification=== | ||
Revision as of 07:34, 16 November 2011
Introduction
The mesoderm forms nearly all the connective tissues of the musculoskeletal system, except within the head where neural crest also contributes connective tissues. Each tissue (cartilage, bone, and muscle) goes through many different mechanisms of differentiation.
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.
The two major parts of the human skeleton are the axial (80 bones in skull, vertebra, ribs, sternum) and appendicular (126 bones in limbs, shoulders, pelvis) skeletons.
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. |
Limb Development
Ossification Centres
Primary Ossification
Secondary Ossification
Bone Structure
Terminology
- Diaphysis - shaft
- Epiphysis - expanded ends
- Metaphysis - connecting region (between diaphysis and epiphysial line)
- Medullary Cavity - (marrow) cavity within the bone. Can also be identified as either red or yellow marrow.
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
- Links: Blood Development
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).[2]
- COL1A1 and COL1A2 mutations
- CRTAP and LEPRE1 mutations, in severe/lethal and recessively inherited osteogenesis imperfecta
References
- ↑ <pubmed>20386744</pubmed>| PMC2851570 | PLoS Genet.
- ↑ <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
External Links
External Links Notice - The dynamic nature of the internet may mean that some of these listed links may no longer function. If the link no longer works search the web with the link text or name. Links to any external commercial sites are provided for information purposes only and should never be considered an endorsement. UNSW Embryology is provided as an educational resource with no clinical information or commercial affiliation.
- Virtual Slidebox of Histology (USA) Skeletal system
- e-radiography Ossification
- UWA Blue Histology bone
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, June 16) 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