Bone Classification & Structure PDF

Professor Lindboom-Broberg (LB) Bone Classification How are bones grouped? Skeletal System Bones (~206 total)  ​Axial skeleton (80 bones) Bones of skull, thorax, and vertebral column  ​Appendicular skeleton (126 bones) Limbs and girdles that attach to the axial skeleton  A...

Professor Lindboom-Broberg (LB) Bone Classification How are bones grouped? Skeletal System Bones (~206 total)  ​Axial skeleton (80 bones) Bones of skull, thorax, and vertebral column  ​Appendicular skeleton (126 bones) Limbs and girdles that attach to the axial skeleton  Associated cartilages  Ligaments and other connective tissues  Functions Support Store minerals & lipids Blood cell production Protections Leverage Bone Classification Six categories of bone based on shape 1. ​ lat bones F 2. ​Sutural bones 3. ​Long bones 4. ​Irregular bones 5. ​Sesamoid bones 6. ​Short bones Bone Classification 1. ​Flat bones Thin, roughly parallel surfaces Protect underlying soft tissues Provide surface area for skeletal muscle attachment Examples: cranial bones, sternum, ribs, scapulae 2. ​Sutural (Wormian) bones Irregular bones formed between cranial bones Number, size, and shape vary Bone Classification 3. ​Long bones Relatively long and slender Examples: various bones of the limbs 4. ​Irregular bones Complex shapes with short, flat, notched, or ridged surfaces Examples: vertebrae, bones of pelvis, facial bones Bone Classification 5. ​Sesamoid bones Small, flat, and somewhat shaped like sesame seed Develop inside tendons (knee, hands, and feet) Individual variation in location and number Example: Patella 6. ​Short bones Small and boxy Examples: bones of the wrist (carpals) and ankles (tarsals) Bone Markings Bone markings (surface features)  Related to particular functions Elevations/projections – Muscle, tendon, and ligament attachment – At joints where adjacent bones articulate Depressions/grooves/tunnels – Sites for blood vessels or nerves to lie alongside or penetrate bone  Professor Lindboom-Broberg (LB) Long Bone Anatomy Anatomical Arrangement Bone Tissues Functions Long Bones Periosteum Endosteum Growth Plate Long Bones Growth and maintenance require blood supply  Vascular features Nutrient artery / vein – Commonly one of each per bone – Nutrient foramen o Tunnel providing access to marrow cavity Metaphyseal artery / vein – Carry blood to/from metaphysis – Connect to epiphyseal arteries/veins  Professor Lindboom-Broberg (LB) Osseous Cells & Tissues Osteoblasts Osteocytes Osteoclasts Compact Bone Spongy Bone Developing Bone  Bone Cells Osteocyte Bone Cells Osteogenic cells (osteoprogenitor cells)  Stem cells producing cells that differentiate into bone producing cells (osteoblasts) Important in fracture repair Locations – Inner lining of periosteum – Lining endosteum in medullary cavity – Lining passageways containing blood vessels Bone Cells Osteoblasts (blast, precursor)  Produce new bony matrix (osteogenesis or ossification) Produces unmineralized matrix (osteoid) Assists in depositing Ca2+ salts to convert osteoid to bone Bone Cells Osteocytes (osteo-, bone + cyte, cell)  Mature osteoblasts that are surrounded by matrix  Unable to divide  Maintain protein and mineral content of surrounding matrix  Occupy pockets called lacunae in bone Remember this term from cartilage? Bone Cells Osteoclasts (klastos, broken)  Remove and remodel bone matrix  Release acids and proteolytic enzymes to dissolve matrix and release stored minerals Process called osteolysis (lysis, loosening) Bone Tissue Bone matrix  Collagen fibers Account for ~1/3 bone weight Provide flexibility  Calcium salts Accounts for ~2/3 bone weight Provides rigidity Calcium phosphate interacts with calcium hydroxide to form crystals of hydroxyapatite salts – Incorporates other salts (calcium carbonate, CaCO3) and ion Compact Bone Osteon Spongy Bone Spongy bone  Lamellae do not grow parallel  Trabeculae Open network of struts and plates deep to compact bone  No blood vessels in matrix Nutrients reach osteons through canaliculi open to trabeculae surfaces  Red bone marrow is found between trabeculae Produces blood cells  Professor Lindboom-Broberg (LB) Bone Growth Interstitial Growth Appositional Growth Bone Growth Ossification: Production of osseous tissue  Appositional Growth  Interstitial Growth Appositional Bone Growth Generalized process 1. Osteoblasts deposit new circumferential lamellae 2. Osteoclasts recycle deeper osteons Appositional Bone Growth Periosteum (fascia)  Wraps the superficial layer of compact bone  Two layers 1. Fibrous outer layer 2. Cellular inner layer  Functions 1. Isolates bone from surrounding tissues 2. Route for blood and nervous supply 3. Actively participates in bone growth and repair  Perforating fibers Protein fibers tying periosteum to osseous tissue Appositional Bone Growth Endosteum  Connective tissue  Incomplete layer lining medullary cavity  Active during bone growth, repair, remodeling  Where layer is incomplete, exposed matrix is remodeled by osteoclasts and osteoblasts Osteoclasts in shallow depressions called osteoclastic crypts (Howship’s lacunae) Endochondral Ossification Endochondral ossification  Process of turning cartilage into bone  Initial embryonic skeleton is made of hyaline cartilage Cartilage expands and is slowly replaced Bone grows in diameter and length Endochondral Ossification Steps in endochondral ossification 1. Cartilage model enlarges Chondrocytes near center of shaft enlarge Enlarged chondrocytes die and disintegrate Disintegration leaves cavities within cartilage Endochondral Ossification Steps in endochondral ossification 2. Blood vessels grow around the edge of the cartilage model Cells of perichondrium convert to osteoblasts Osteoblasts form superficial layer of bone along the shaft Endochondral Ossification Steps in endochondral ossification 3. Blood vessels penetrate cartilage and enter central region Entering fibroblasts differentiate into osteoblasts Primary ossification center: Spongy bone production begins Bone formation spreads along the shaft toward both ends Endochondral Ossification Steps in endochondral ossification 4. Growth & remodeling Medullary cavity created Osseous tissue of the shaft thickens Cartilage near the epiphyses is replaced by shafts of bone Bone grows in length and diameter Endochondral Ossification Steps in endochondral ossification 5. Capillaries and osteoblasts migrate into the epiphyses Create secondary ossification centers 6. Epiphyses fill with spongy bone Articular cartilage remains exposed to joint cavity Epiphyseal cartilage separates epiphysis from diaphysis Endochondral Ossification Steps in endochondral ossification 7. Interstitial Growth Endochondral Ossification  At puberty, hormones stimulate increased bone growth, and epiphyseal cartilage is replaced Osteoblasts produce bone faster than chondrocytes produce cartilage Epiphyseal cartilage narrows until it disappears – Process called epiphyseal closure – Leaves epiphyseal line in adults  Professor Lindboom-Broberg (LB) Bone Fractures Anatomical Arrangement Bone Tissues Functions Bone Fracture Fracture  Crack or break due to extreme mechanical stress  Most heal as long as blood supply and cellular parts of periosteum and endosteum survive  Repair involves four steps Bone Fracture General categories of fractures  Closed / simple No break in skin Only seen on x-rays  Open / compound Project through the skin More dangerous due to: – Infection – Uncontrolled bleeding  There are many specific fracture types Bone Fracture  Transverse fractures Break shaft perpendicular across long axis  Spiral fractures Produced by twisting stresses Spreads along length of bone Typically oblique Bone Fracture  Compression fractures Occur in vertebrae subjected to extreme stresses Often associated with osteoporosis  Greenstick fractures One side of shaft broken, one side bent Generally occurs in children – Long bones have yet to fully ossify Bone Fracture  Displaced fractures Produce new and abnormal bone arrangements Nondisplaced fractures retain normal alignment  Comminuted fractures Shatter affected area producing fragments Bone Fracture  Epiphyseal fractures Occur where bone matrix is calcifying A clean transverse fracture of this type heals well If not monitored, breaks between epiphyseal plate and cartilage can stop growth at site Bone Fracture Fracture Repair (4 steps) 1. ​Fracture hematoma formation Large clot closes injured vessels Develops within several hours Bone Fracture Fracture Repair (4 steps) 2. Callus formation Internal callus – Network of spongy bone – Unites inner edges of fracture External callus – Composed of cartilage and bone – Stabilizes outer edges of fracture Bone Fracture Fracture Repair (4 steps) 3. Spongy bone formation Cartilage of external callus replaced by spongy bone Bone fragments and dead bone are removed and replaced Ends of fracture held firmly in place Bone Fracture Fracture Repair (4 steps) 4. Compact bone formation Spongy bone replaced by compact bone Remodeling over time eliminates evidence of fracture  Professor Lindboom-Broberg (LB) Skeletal Abnormalities Inadequate GH Too much GH Slow growth rate Fast growth rate Congenital Nutritional Age-related Bone Growth Abnormalities Shortened Bones  Disorder resulting in stunted growth  CAUSE Pituitary failure Inadequate Growth Hormone (GH)  RESULTS Reduced epiphyseal cartilage activity; abnormally short bones  TREATMENT Treat with synthetic GH Rare in United States due to treatment Bone Growth Abnormalities Gigantism  Disorder causing lengthened bones  CAUSE Pituitary tumor most common Overproduction of growth hormone before puberty  TREAMENT Surgery, radiation, or medications suppressing growth hormone release  FACTS Can reach heights of over 2.7 m (8 ft. 11 in.) Puberty often delayed Bone Growth Abnormalities Acromegaly  Disorder causing growth in adulthood  CAUSE Overacivity pituitary Overproduction of growth hormone after epiphyseal plates close  RESULTS Bones get thicker, not longer (especially face, jaw, and hands) Alterations in soft-tissue structure changes physical features  TREATMENT Decrease pituitary activity Bone Growth Abnormalities Shortened Bones  Achondroplasia Disorder limiting cartilage growth  CAUSE Epiphyseal cartilage of long bones grows slowly  RESULTS Replaced by bone early in life Short, stocky limbs result Trunk is normal size No effects on sexual or mental development  TREATMENT GH supplementation Surgery (to alleviate symptoms) Bone Growth Abnormalities Lengthened Bones  Marfan syndrome Inherited metabolic condition  CAUSE Excessive cartilage formation at epiphyseal cartilages  RESULTS Very tall person with long, slender limbs Affects other connective tissues throughout the body – Commonly causes cardiovascular problems  TREATMENTS Based on symptoms (medicines for heart, surgery for lungs, etc) Bone Growth Abnormalities Ricketts  Softening/weakening of bones due to low hydroxyapatite  CAUSE Decreased hydroxyapatite Possibly low vitamin D, calcium, or hormone levels Rare to be genetic causes  RESULTS Decreased bone hardness Bones under excess stress begin to bow  TREATMENT Vitamin D & Calcium Supplements Bone Changes with Age Bone changes with aging  Osteoporosis (porosus,  Osteopenia (penia, lacking) porous) Inadequate ossification Bone loss sufficient to leading to loss of bone affect normal function mass Often occurs with age, beginning at 30 & 40 More severe in women Bone Changes with Age Bone Density  Testing Done with multiple scanning technologies – Central test – measures hip and/or vertebrae – Peripheral test – measures arm, leg, finger, heel, etc.  Scoring T-score: A measurement of how dense the bone is compared to a healthy 30-year old. – -1.0 = above normal – -1.0 to -2.5 = osteopenia – -2.5 or lower = osteoporosis Bone Changes with Age Bone Density  Affect Osteoporosis causes 8.9 million fractures per year – One fracture every 3 seconds 1 in 3 women (>50) will have an osteoporotic fracture 1 in 5 men (>50) will have an osteoporotic fracture Hip fractures – 75% women, 25% are men – 20-24% mortality rate within 12 months (women fair better than men)  Treatment Diet Medications Movement / Stress Limiting risk of fracture