11. Skeletal System Devo Flashcards
The initial progenitor tissue of all musculoskeletal (MS) tissues is
mesenchyme… referred to as Skeletal Tissue Forming Mesenchyme (STFM). The STFM is derived from several sources.
Vertebrae and ribs come from
Scleratome tissue of the somites
Sternum comes from
Somatic mesoderm of ventral body wall
Skull comes from
Head mesoderm
Scleratome tissue of occipital somites,
Neural crest ectomesenchyme
appendicular skeleton (bones of the limbs and limb girdles) is derived from
Somatic Mesoderm.
What are the developmental phases for skeletal tissues?
The cells in skeletal precursor tissues have a mesenchyme phenotype. Once they have received inductive signals, the mesenchyme cells condense into Preskeletal Mesenchyme Condensations (PMC) sometimes called a blastema. Inductive signals for PMC are often derived from an adjacent epithelium.
method of forming bone Directly From
Mesenchyme without a cartilage intermediate.
Intramembranous Ossification
Signals, most likely from the adjacent epithelium, result in expression of____________ in the mesenchymal
cells that then differentiate into osteoblasts (bone-forming cells). T
bone master gene Runx-2
osteoblasts fnx
produce bone specific proteins and begin to deposit radiating spicules of osteoid matrix (pre-bone) around them. Further osteoblast activity results in mineralization of the osteoid matrix.
What bones are formed by intramembranous ossification?
Bones formed by this method include the flat bones of the face and skull. Growth of these bones is achieved
by adding bone to the outer surface and removing it from the inner surface.
method of forming bone that makes use of Cartilage Intermediates (models).
Endochondral Ossification (The mesenchyme initially aggregates into a pre-skeletal mesenchymal condensation)
Centrally placed cells in Endochondral ossification express what gene:
express the cartilage master gene Sox-9 and differentiate into chondrocytes.
Sox-9 master gene causes what?
causes differentiation into chondrocytes
When Sox-9 is expressed… what affect does it have on chondrocytes
chondrocytes enlarge, secrete cartilage matrix, and form a cartilage intermediate or ‘model’ for the bone.
mesenchymal cells at periphery of cartilage element form a fibrous capsule called the perichondrium. ______ can influence some to express Runx-2 to differentiation to osteoblasts
Indian hedgehod (Ihh)
chondrocytes within the cartilage
model are influenced by Ihh (in some cases Runx2) expression and begin to hypertrophy and secrete
type X collagen
Chondrocytes influenced by Ihh expression begin to hypertrophy and sectrete type X collagen… Hypertrophied chondrotcytes produce:
vascular endothelial growth factor (Vegf) that stimulates blood vessel ingrowth resulting in accumulation of additional osteoblasts.
The cartilage model is eventually replaced by bone. Most bones of the body ossify by this method.
Endochondral ossification
Many of them grow lengthwise (long bones of the limbs and trunk) by maintaining a plate of cartilage at one or both ends.
What is the role of the runx-2 gene in bone development?
A cell that expresses the Runx-2 will become an Osteoblast
A cell that expressed the Sox-9 will become a
Chondroblast.
These skeletal tissue forming master genes in turn stimulate the expression of additional genes specific to osteoblasts or chondroblasts resulting in the formation of bone or cartilage.
Sox-9 and Runx-2
What is the Primary Ossification Center
Primary Ossification Center is the area of a pre-skeletal mesenchyme condensation or cartilage intermediate that is the First to Ossify. In long bones, it is usually in the center of the shaft, while in flat bones it is usually in the center of the mesenchyme condensation. A bone may have more than one primary ossification center
Secondary Ossification Center
additional areas of ossification that appear
in the Prenatal, Postnatal, or Post pubertal period
appear in the epiphyses of long bones during the first few years after birth or the tips of vertebrae processes and the cranial and caudal surfaces of vertebral bodies after puberty.disappear by age 20 to 30
amount of Epiphyseal Cartilage Retained in the Skeleton.
Bone Age
