DSF Histo of Bone Flashcards
Chondrocytes
Cartilage cells
Cartilage types
Hyaline
Elastic
Fibrocartilage
Hyaline cartilage
Most common cartilage type, appears glassy
Found in nasal septum, tracheal rings, larynx, sternal rib ends, articular surfaces of joints
4 roles:
Provide low-friction surface
Helps lubricate synovial joints
Distributes mechanical forces to underlying bone tissue
Forms precursor of bone in developing skeleton
4 roles of Hyaline cartilage
Provide low-friction surface
Helps lubricate synovial joints
Distributes mechanical forces to underlying bone tissue
Forms precursor of bone in developing skeleton
Perichondrium
Dense irregular fibrous tissue Firmly attached Cells indistinguishable from fibroblasts Source for new chondrocytes Does NOT cover articular cartilage
What is hyaline cartilage made up of? How is it made?
Hyaline cartilage is highly hydratedL 60-80% of net weight is intercellular water
Chondrocytes produce hyaline cartilage matrix
3 majors classes of molecule:
Type II collagen fibers
Proteoglycans (mostly GAGs)
Multi-adhesive glycoproteins
How are chondrocytes arranged?
Chondrocytes distributed either singularly or in clusters
Clusters = Isogenous groups, usually 2-4 cells
Isogenous groups represent cells that have only recently divided
Where is elastic cartilage found?
External ear, walls of external acoustic meatus, auditory tube, epiglottis of larynx
What is elastic cartilage made up of?
Has same ground substance for matrix but contains elastic fibers and elastic lamellae
Has perichondrium
Fibrocartilage
Combination of hyaline cartilage and dense regular CT
Characterized by significant quantities of both type I and II collagen fibers as well as hyaline ground substance
NO perichondrium
Histo: row-like appearance of cells
Considerably less matrix/ground substance
Chondrogenesis
Process of cartilage development
Differentiation of stellate shaped primitive mesenchymal cells to form chondroblasts (cartilage precursor cells)
2 processes -
Appositional growth: New cartilage cells derived from inner portion of the surrounding perichondrium
Interstitial growth: Mitotic division of the chondrocytes
Chondroblasts
Cartilage precursor cells
What is bone made up of?
90% collagen by weight - flexible/tensile strength
Hydroxyapatite (mineral) - compressive strength
Type I collagen = Major structural component
Woven bone
(Immature bone) Disorganized Non-lamellar Rapidly formed More ground substance than mature bone
Osteoprogenitor cells
New bone formation
Derived from mesenchymal cells
Periosteum and endosteum contains the osteoprogenitor cells
Appear flattened/squamous w/ light staining and elongate/ovoid nuclei
Osteoblasts
Maintains ability to divide, and secretes both type I collagen and bone matrix proteins (osteoid) that later becomes calcified
Secrete mineral vesicles
Euchromatic, extensive rER, Golgi, vesicles w/ alkaline phosphatase, lipid, gap junctions
*Have receptors for PTH
Recruit and regulate osteoclasts by secreting essential GFs, CSF-1 (M-CSF) and RANKL
Histo: Cuboidal single layer of cells in apposition to forming bone
Osteocytes
10-20% of osteoblasts become osteocytes
Cell volume decreases by 70%: ~50 cell processes develop, takes 3 days
Osteocytes = >90% of bone
Maintain, communicate condition to surface via gap junctions
Osteoclasts
Large, multiple nuclei
Differentiate from hemopoetic progenitor cells, mature under control of RANK-RANKL signaling mech
Resoprtion Bay (Howship Lacunae)
Actin ring (“clear zone”) to attach very tightly to bone
Ruffled border
Marked acidophilia - acid used to breakdown bone
“Coupling” b/w Bone Formation and Bone Resorption
Mechano-sensation and Transduction
During growth, bone formation > bone resoprtion
Adulthood, bone formation = bone resorption
Old age, bone formation < bone resorption
*Both sides controlled by many systemic and local factors - endocrines, minerals, vitamins, GFs, mechanical loading, inflammation, etc.
2 non-exclusive mechanisms of bone growth and formation
Intramembranous
Endochondral
Intramembranous Ossification
Occurs directly via condensations of mesenchymal cells that differentiate to osteoblasts and secrete bone matrix
True for “flat” bones of cranial vault, clavicles, anterior mandible
Endochondral Ossification
- Mesenchymal condensation to cartilage model
- Chondrocyte hypertrophy
- Cartilage mineralizes, bone collar forms
- Vascular invasion, cartilage replaced by bone
5 zones of Epiphyseal Plate
- Zone of reserve cartilage*: Typical hyaline cartilage
- Zone of proliferation*: Clusters of cells undergo mitotic division and organize into distinct columns, secrete matrix
- Zone of hypertrophy*: Chondrocytes can increase 10X in height, driving bone elongation, Cartilage matrix becomes compressed forming linear bands b/w the columns
- Zone of calcified cartilage*: Matrix becomes calcified and the cartilage cells begin to degenerate, Proximal chondrocytes begin to undergo apoptosis
- Zone of resorption*: Nearest diaphysis, Capillaries and osteoprogenitor cells begin to invade the region as spear-shaped “longitudinal spicules”
Direct bone repair
External fixation of the damaged site, followed by normal internal remodeling process
Indirect bone repair
Usually begins as inflammatory response:
Hematoma - Granulation tissue - FIbrocartilaginous - Soft callus - Bony callus
Perichondrium
Membrane covering elastic cartilage, equivalent to periosteum surrounding bone
Does elastic cartilage calcify with age?
NO - b/c flexible
Where is fibrous cartilage found?
High force environments - shock absorber
Intervertebral discs, pubic symphsis, articular discs or TMJ and sternoclavicular joint, menisci of knee, triangular cartilage of wrist
Components of Ground Substance of Bone
Proteoglycans (GAGs and core protein)
Multi-adhesive proteins - facilitate interaction w/ matrix
Osteonectin - hydroxyapatite attachment
Osteopontin - cell to matrix attachment
Bone sialoproteins - mineralization process
BMPs (bone mineralization GFs) - able to induce differentiation of osteoblasts
Cytokines
Other GFs
