Lecture 8 Flashcards
OSTEOCLAST FORMATION REGULATION AND ACTIVITY (3 STEPS)
- ) PROLIFERATION/DIFFERENTIATION - MONONUCLEAR PRECURSOR CELLS W/ HEMATOPOIETIC LINEAGE FUSE => MULTINUCLEATED OSTEOCLASTS
- ) ACTIVATION OF OSTEOCLAST PRECURSOR WHEN RANKL BINDS TO RANK ON OSTEOCLAST SURFACE (OPG CAN INTERFERE W/ THIS REACTION AND STOP OSTEOCLAST ACTIVATION BY BINDING TO RANKL)
- ) RUFFLED MEMBRANE SECRETES H+ ENZYMES => ACIDIC ENVIRONMENT (PROMOTES DEGRADATION OF ORGANIC/INORGANIC PORTION OF BONE INTO COMPARTMENT
RUFFLED MEMBRANE
- CA CATALYZES FORMATION OF H2O AND CO2 W/IN RUFFLED MEMBRANE AND COMBINES THEM TO FORM BICARBONATE (PROVIDES H+ IONS FOR ACIDIC ENVIRONMENT)
- DEGRADATION PRODUCTS FROM BREAKDOWN OF BONE INTO CA2+ AND PO4(3-) AND COLLAGEN FRAGMENTS ARE REABSORBED BY RUFFLED MEMBRANE AND EXCRETED VIA VESICULAR EXCRETION
ENZYMES INVOLVED IN OSTEOCLASTIC BONE BREAKDOWN
1.) LYSOSOMAL ENZYMES
2.) MATRIX METALLOPROTEINASES
RELATIONSHIP BETWEEN ENZYMATIC AND CHEMICAL ACTIVITY IS IMPORTANT
TUMOR CELL EFFECTS ON OSTEOCLASTIC ACTIVITY
TUMOR CELLS PRODUCE FACTORS (PTHrP - PARATHYROID HORMONE-RELATED PROTEIN) THAT PROMOTE FORMATION/ACTIVATION OF OSTEOCLASTS => BONE RESORPTION AND RELEASE OF FACTORS BY BONE MATRIX (TGF-β) WHICH STIMULATES TUMOR CELL PROLIFERATION
PTHrP
BLOCKS OPG AND ACTIVATES RANKL
BONE GROWTH
BONE GROWS IN LENGTH @ THESE VARIOUS SITES -
1) CARTILAGE GROWS ON THE ENDS OF THE ARTICULAR CARTILAGE
2) CARTILAGE REPLACED BY BONE ON THE INSIDE OF THE ARTICULAR CARTILAGE
3) CARTILAGE GROWS AT THE EPIPHYSEAL PLATE OUTER EDGE
4) CARTILAGE REPLACED BY BONE AT THE EPIPHYSEAL PLATE INNER EDGE
THIS OCCURS UNTIL EPIPHYSEAL PLATES (COMPOSED OF HYALIN CARTILAGE) CLOSE
BONE REMODELING IN SPONGY/CORTICAL BONE
DIAPHYSIS IS REMODELED -
SPONGY BONE IS REMODELED EVERY 3-4 YEARS
CORTICAL BONE IS REMODELED EVERY 10 YEARS
PROCESS IS CONTINUAL - NEVER AT METABOLIC REST
PRODUCES LYSOSOMAL ENZYMES AND ACIDS
BONE REMODELING
- ) BONE RESORBED AT BONE HEAD/NECK JUNCTURE
- ) BONE ADDED BY APPOSITIONAL GROWTH AT THE SURFACE OF THE EXTERIOR DIAPHYSIS
- ) BONE RESORBED ON THE INTERIOR SURFACE OF THE DIAPHYSIS
REMODELING UNITS
MADE UP OF A COMPOSITE OF OSTEOBLASTS AND OSTEOCLASTS
EPIPHYSEAL PLATE CARTILAGE ORGANIZATION
Real People Have Career Options
- ) RESTING ZONE - SMALL INACTIVE CARTILAGE CELLS
- ) PROLIFERATION ZONE - QUICKLY DIVIDING (REPEATED MITOSIS) CHONDROBLASTS (PUSH EPIPHYSIS AWAY FROM DIAPHYSIS => LENGTHENING)
- ) HYPERTROPHIC ZONE - OLDER CHONDROCYTES ENLARGE AND SIGNAL TO THE SURROUNDING MATRIX TO CALCIFY
- ) CALCIFICATION ZONE - MATRIX BECOMES CALCIFIED AND CHONDROCYTES DIE LEAVING BONE-LIKE TISSUE (NOT BONE YET)
- ) OSSIFICATION ZONE - OSTEOCLASTS DIGEST CALCIFIED CARTILAGE AND OSTEOBLASTS REPLACE IT W/ ACTUAL BONE TISSUE IN THE SHAPE OF CALCIFIED CARTILAGE => BONE TRABECULAE
FUSION OF EPIPHYSIS
AT FULL BONE LENGTH CELLS IN EPIPHYSEAL CARTILAGE STOP PROLIFERATING AND BONES OF DIAPHYSIS AND EPIPHYSIS THEN BECOMES CONTINUOUS
ACHONDROPLASIA
DEFECT IN CARTILAGE FORMATION (MOST COMMON CAUSE = DWARFISM)
SALTER-HARRIS FRACTURES
INVOLVE EPIPHYSEAL PLATES (INTERFERES W/ GROWTH AND HEIGHT)
OSGOOD-SCHLATTER DISEASE
STRESS ON EPIPHYSEAL PLATES IN THE TIBIA LEAD TO EXCESS BONE GROWTH AND A PAINFUL LUMP IN THE BONE
SOMATOTROPIN
PRIMARY GROWTH FACTOR THAT AFFECTS BONE GROWTH
STARTS IN THE HYPOTHALAMUS
-TROPIN = TO NOURISH/STIMULATE