Musculoskeletal System 1 Flashcards
What cells do all bones arrise from?
Mesenchymal cells
What are the 2 types of bone formation?
Intramembranous
Endochondral
Define intramembranous bone formation
Direct conversion of mesenchymal cells into bone
What type of bones undergo intramembranous formation?
Flat bones
Explain intramembranous formation
- Ossification center appears in the fibrous connective tissue membrane
- Selected centraly located mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center - Bone matrix (osteoid) is secreted within the fibrous membrane
- Osteoblasts begin to secret osteoid, which is mineralized within a few days
- Trapped osteoblasts become osteocytes - Woven bone and periosteum form
- Accumulating osteoid is laid down between embryonic blood vessels, which form a random network. The result is a network of trabeculae
- Vascularized mesenchyme condenses on the external face of the woven bone and becomes periosteum - Bone collar of compact bone forms and red marrow appears
- Trabeculae just deep to the periosteum thicken, forming a woven bone collar that is later replaced with mature lamellar bone
- Spongy bone, consisting of distinct trabeculae, persists internally and its vascular tissue becomes red marrow
What is responsible for formation of trebeculae?
Infiltration of blood vessels
What dictates the shape of the skull?
Each species has a dictated time for closure of suture and this is what dictates the shape of the skull
Define Endochondral ossification
Mesenchymal cells first differentiate into cartilage which is later replaced by bone
5 steps of osteogenesis of long bones by enochondral ossification
- Hyaline cartilage calcifies and periosteal bone collar forms around diaphysis
- Primary ossification center forms in the diaphysis
- Secondary ossification centers form in epiphyses
- Bone replaces cartilage, except the articular cartilage and epiphyseal plates
- Epiphyseal plates ossify and form epiphyseal lines
What does notochord induce the surrounding mesenchym to secrete
epimorphin - attracts sclerotome to migrate
What do sclerotome cells differentiate into?
Chondroblast and chondrocytes
What is the primarily cranial portion of somite 5?
Atlas
What is the cranial portion, head and tubercle of ribs, derived from?
Dense portion
What is the shaft of rib derived from?
Diffuse Portion
What makes up cartialge matrix?
First 9 ribs that go around thorax and meet ventrally
What creates the sternum?
Fusion of cartilage matrix at midline
What is block vertebrae?
Defect in resegmentation
- typically does not cause any clinical signs
What is hemivertebrae?
Wedge shaped vertebrae
3 defects of hemivertebrae
Defect in cartilagenous model
Defect in resegmentation
Defect in calcification
What causes the biggest problem in hemivertebrae?
Cervical vertebrae
- wobblers - common in horses and large dogs
What is atlantoaxial subluxation?
Instability of C1 and C2
What causes atlantoaxial subluxation?
Defect of resegmentation of C1 and C2
What is the dens
Protuberance of the axis
What is the problem with no dens?
Nothing to keep the axis from dislocating
What is a hereditary disease in arabian horses?
Occipitoatlantoaxial malformation (OAAM)
8 points of interest with Occipitoatlantoaxial malformation (OAAM)
- Malformation in resegmentation
- Small foramen magnum
- Fusion of C1 to occipital part of skull
- Atlantol foramen is smaller
- Dens is hypoblastic
- Caudal articular surface of atlas resembles the occipital condyle
- Axis has broad transverse processes like atlas
- Transverse process of C2 are hypoblastic
Common problem on hobby farms with ovine>
Ovine hereditary chondrodysplasia
- abnormal cartialge production
- Chondrocytes are disorderly
- abnormal endochondral ossification
