Physis Flashcards
Physis Zones
B=reserve
C=proliferative
D=Hypertrophic
E=metaphysis (primary and secondary spongiosa)
major regulator of chondrogenesis
Sox-9
Sox-9
major regulator of chondrogenesis
regulates several cartilage-specific genes during endochondral ossification, including collagen types II, IV, and XI and aggrecan
major source of nutrition to physis
perichondrial artery
zones with disease figure
Reserve Zone diseases (4)
Gaucher’s
DD
(Kneist/Pseudoachon)
Proliferative Zone Diseases (3)
Achondroplasia
Gigantism
(MHE)
Hypertrophic Zone diseases (10)
SCFE (not renal)
Rickets (PCZ)
Salter Harris Fx (PCZ)
Enchondromas
Mucopolysach
SED/MED
Schmids/Kniest/Pseudoachon
PCZ = “provisional calcification zone”
Primary spongiosa zone (metaphysis) diseases (2)
corner fx
Scurvy
Secondary spongiosa zone (metaphysis) diseases
Renal SCFE
When does embryonic long bone formation commence?
6th week in utero (formed from mesenchymal analge)
Steps in embryonic long bone formation
- vascular buds invade the mesenchymal model
- primary ossification centers form at ~ 8 weeks osteoprogenitor cells migrate through vascular buds and differentiate into osteoblasts forming the primary ossification centers
- cartilage model forms and grows
- marrow is formed by resorption of central portion of the cartilage anlage by myeloid precursor cells that migrate in through the vascular buds
- secondary ossification centers form and develop at bone ends and lead to epiphyseal ossification center (growth plate)
Biochem physis - Reserve zone
a. Has the lowest intracellular and ionized calcium content.
b. Oxygen tension is low.
Biochem physis - Proliferative zone
a. Oxygen tension is highest in this zone secondary to its rich vascular supply.
b. The presence of abundant glycogen stores and a high oxygen tension supports aerobic metabolism in the proliferative chondrocyte.
Biochem physis - Hypertrophic zone
a. Oxygen tension low (avascular), energy production = anaerobic glycolysis
b. In the upper hypertrophic zone, a switch from adenosine triphosphate (ATP) production to calcium production occurs. Once the glycogen stores have been depleted, calcium is released. This is the mechanism by which the matrix is calcified.
c. The region of the hypertrophic zone where mineralization occurs is known as the zone of provisional calcification.
d. Slipped capital femoral epiphysis (SCFE) involves the hypertrophic zone.
Metaphysis biochem
Characterized by anaerobic metabolism, vascular stasis, and low oxygen tension. This is secondary to the blood supply to the region.
b. After the removal process is complete, osteoblasts begin the remodeling process, in which the osteoblasts progressively lay down bone on the cartilage template, creating an area of woven bone on a central core that is known as primary trabecular bone. The primary trabecular bone is resorbed via osteoclastic activity and replaced by lamellar bone, which represents the secondary bony trabeculae.
c. This remodeling process occurs around the periphery and subperiosteal regions of the metaphysis and results in funnelization, a narrowing of the diameter of the metaphysis to meet the diaphysis.
rate of chondrocyte maturation in the growth plate
Local growth factors directly regulate the rate of chondrocyte maturation in the growth plate.
A signaling loop involving parathyroid-related peptide (PTHrP), which is a potent inhibitor of chondrocyte maturation, and indian hedgehog has been well described.
Indian hedgehog is produced by growth plate chondrocytes and regulates the expression of PTHrP
