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BMS 250 Lecture
Chapter 7
| Term | Definition |
|---|---|
| Skeletal System | dynamic, living tissue that interacts with all other body systems; consists of bone, cartilage, ligaments, tendons, and articulation structures |
| Compact bone | cortical, dense, rigid connective tissue; white smooth, and solid; withstands mechanical stress, 80% of total bone mass |
| Spongey bone | cancellous, trabecular, porous; located internal to compact bone; stores bone marrow, distributes stress; 20% of total bone mass |
| What is compact bone made up of? | osteons |
| What is spongey bone made up of? | trabeculae with marrow in the spaces |
| Trabeculae | latticework of thin plates, parallel lamellae |
| Cartilage in the human skeleton | hyaline cartilage and fibrocartilage |
| Hyaline cartilage locations | located in the fetal skeleton, costal cartilage, articular cartilage, and epiphyseal plate |
| Fibrocartilage locations | intervertebral discs, pubic symphysis, menisci of the bone |
| General functions of bone | support and protection, movement (as levers), hemopoieses, storage of minerals, and energy reserve |
| What minerals does bone store? | calcium and phosphate |
| Hemopoiesis/hematopoiesis | blood cell production in bone marrow |
| Calcium | aids in muscle contraction, blood clotting, and neurotransmitter release |
| Phosphate | functions through nucleotides and phospholipids |
| Four classifications of bone | long, short, flat, irregular |
| Long bones | bones that are longer than they are wide |
| Short bones | bones where the length and width is equals |
| Flat bones | bones with a thin, possibly curved surface |
| Irregular bones | bones that are elaborate and sometimes have a complex shape |
| Diaphysis | the shaft of a bone |
| Medullary cavity | hollow space within the diaphysis |
| Epiphysis | expanded end that is proximal or distal |
| Metaphysis | junction between diaphysis and epiphysis |
| Epiphyseal plate | layer of hyaline cartilage permitting lengthwise growth during childhood |
| Periosteum | protective sheath surrounds all but areas covered by articular cartilage; consists of dense irregular connective tissue |
| Fibrous layer of the periosteum | composed of dense irregular CT, provides protection and is an anchoring site |
| Cellular layer of the periosteum | contains osteoprogenitor cells, osteoblasts, and osteoclasts |
| Perforating fibers of the periosteum | collagen fibers anchoring periosteum to bone |
| Endosteum | incomplete layer of cells covering internal surface of medullary cavity; cells include osteoprogenitor cells, osteoblasts, and osteoclasts |
| Nutrient foramen | opening through which blood vessels and nerves enter and exit |
| Gross anatomy of short, flat, and irregular bones... | external surface: compact bone, internal surface: spongey bone with no medullary cavity |
| Red bone marrow (myeloid tissue) | reticular CT, immature blood cells and fat; function: hemopoiesis |
| Yellow bone marrow | adipose tissue; function: energy reserve |
| In children, most bone marrow is... | red bone marrow |
| In adults, most bone marrow is... | yellow. Red bone marrow remains in only portions of the axial skeleton and proximal epiphysis of the humerus and femur |
| Osteoprogenitor cells | stems cells; divide to generate 1 stem cell and 1 "committed cell" (an osteblast) |
| Osteoblasts | perform bone deposition; secrete osteoid and regulate mineralization; have a cuboidal shape with an abundant rough ER and golgi; become trapped in the bone matrix and differentiate into osteocytes |
| Osteocytes | mature bone cells; no bone forming ability; functions: mechanosensation, orchestrate bone remodeling; in lacunae in compact and spongey bone |
| Osteoclasts | large, multinuclear phagocytic cells; located within/near pit on surface of bone called resorption lacuna; performs bone resorption |
| Components of the extracellular matrix of bone | organic component and inorganic component |
| Organic component of the extracellular matrix | osteoid (collagen fibers, ground substance of glycosaminoglycans, proteoglycans & glycoproteins); resists torsion and tactile forces |
| Inorganic component of the extracellular matrix | Hydroxyapatite crystals (Calcium phosphate, calcium hydroxide, incorporate other salts and ions); resists compressional forces, gives stiffness to bones |
| Calcification | osteoblasts secrete semisolid osteoid; hydroxyapatite crystals deposit around collagen fibers (requires vitamin D and C) |
| Bone resorption | breakdown of bone tissue; osteoclasts secrete proteolytic enzymes that digest the organic components of the ECM and hydrochloric acid to dissolve inorganic components |
| Why are there 2 components of the bone matrix? | heat will destroy the organic matrix and denature the collagen protein fibers; acid will dissolve the inorganic matrix and breakdown the hydroxyapatite crystals and mineral salts |
| When does cartilage growth begin? | during embryological development |
| Two types of cartilage growth | interstitial and appositional growth |
| Interstitial cartilage growth | growth in length in internal regions; chondrocytes begin mitosis, 2 chondroblasts in a single lacuna, cblasts pushed apart & secrete new cartilage matrix to become chondrocytes in own lacuna, cartilage grows internally as chondrocytes secrete more matrix |
| Appositional cartilage growth | growth in width; stem cell at edge of perichondrium divides, produces new undifferentiated stem cells & new chondroblasts at the periphery, chondroblasts are pushed apart as they secrete new cartilage matrix, becoming chondrocytes in own lacuna |
| Stages of cartilage growth | early embryo development: both interstitial and appositional growth occur, cartilage begins to mature- interstitial growth declines &it is primarily appositional growth, cartilage fully mature: new cartilage growth is limited and occurs only after injury |
| Types of bone formation | intramembranous ossification and endochondral ossification |
| Ossification/osteogenesis | formation and development of bone CT begins in the embryo (8th-12th week), continues through adolescence |
| Intramembranous ossification | bone growth within mesenchyme membrane; produces flat bones of the skull, some facial bones, the mandible, and the central part of the clavicle |
| Steps of intramembranous ossification | ossification center forms within thickened mesenchyme, osteoid matrix forms and osteoid undergoes calcification, immature woven bone and surrounding periosteum form, lamellar bone replaces woven bone forming compact and spongey bone |
| Endochondral ossification | begins with a hyaline cartilage model, produces most bones of the skeleton- the upper and lower limbs, the pelvic, the vertebrae, and the ends of the clavicle |
| Steps of endochondral ossification | hyaline cartilage model develops, cartilage calcifies & bone collar forms, bone replaces hyaline cartilage in diaphysis, then in epiphyses, cartilage replaced by bone except articular & epiphyseal plate, epiphyseal plate ossifies & forms epiphyseal line |
| Step 1 of endochondral ossification | fetal hyaline cartilage model develops during the 8th-12th week of development; chondroblasts secrete cartilage matrix (interstitial and appositional cartilage growth), perichondrium surrounds cartilage |
| Step 2 of endochondral ossification | chondrocytes in diaphysis hypertrophy & resorb some matrix, chondrocytes die due to matrix calcification, blood vessels penetrate perichondrium around shaft changing it to periosteum, stem cells make osteoblasts secreting osteoid &form bone collar |
| Step 3 of endochondral ossification | primaryossificationcenterformsindiaphysis-periostealbud extends from periosteum into core of cartilage shaft, oblasts start producing osteoid using calcified cartilage as template in the primary ossification center, ossification begins in both directions |
| Step 4 of endochondral ossification | secondary ossification center forms in epiphysis- process that formed primary ossification begins in epiphyses around time of birth, osteoblasts resorb some bone matrix within diaphysis creating the hollow medullary cavity |
| Step 5 of endochondral ossification | bone replaces all cartilage except articular and epiphyseal plate |
| Step 6 of endochondral ossification | bone continues to grow lengthwise until epiphyseal plate ossifies to form epiphyseal line (anatomical neck) |
| Interstitial bone growth | growth in length, dependent on growth of cartilage within epiphyseal plate |
| Zone 1 of interstitial bone growth | resting cartilage- nearest epiphysis (secures it to the epiphyseal plate), small chondrocytes; resembles mature, healthy, hyaline cartilage |
| Zone 2 of interstitial bone growth | proliferating cartilage- chondrocytes undergo rapid mitotic cells division and enlarge; align in longitudinal columns of flattened lacuna parallel to diaphysis |
| Zone 3 of interstitial bone growth | hypertrophic cartilage- chondrocytes cease dividing and hypertrophy; chondrocytes start resorbing cartilage matrix (which thins lacuna walls) |
| Zone 4 of interstitial bone growth | calcified cartilage- 2-3 layers of chondrocytes in an opaque matrix, minerals deposit in between the columns of chondrocytes, the calcification destroys the chondrocytes |
| Zone 5 of interstitial bone growth | ossification- lacuna walls breakdown forming longitudinal channels; capillaries and osteoprogenitor cells from medullary cavity invade these spaces; new bone matrix is deposited on remaining calcified cartilage matrix |
| In what zone of interstitial bone growth does the bone grow in length? | zone 3 |
| How does bone growth in length stop? | rate of epiphyseal cartilage production slows, rate of osteoblasts activity accelerates, epiphyseal plate narrows (disappears leaving an epiphyseal line) |
| Appositional bone growth | occurs within the periosteum; osteoblasts in inner cellular layer deposit matrix in layers called external circumferential lamellae; osteoclasts along medullary cavity resorb matrix to expand the medullary cavity |
| Bone remodeling | dynamic, ongoing process that renews and reshapes bone throughout our lifetime; new bone tissue replaces old bone tissue |
| What is bone remodeling dependent upon? | coordinated activity of osteoblasts, osteocytes, and osteoclasts |
| Factors influencing bone remodeling | mechanical stress and hormones |
| Stages of bone remodeling | bone resorption, reversal, bone deposition, and termination |
| Bone resorption stage of bone remodeling | breakdown of bone tissue; osteoclasts develop within a remodeling site, osteoclasts form a resorption lacunae and breakdown the matrix (dissolves hydroxyapatite crystals), proteolytic enzymes digest osteoid |
| Reversal stage of bone remodeling | reversal cells prepare for subsequent bone formation; remove debris and undigested collagen fibers, secrete chemical signals that recruit osteoprogenitor cells |
| Bone deposition stage of bone remodeling | bone formation; osteoprogenitor cells return to remodel site and differentiate into osteoblasts; osteoblasts secrete osteoid and mineralization-promoting substances, hydroxyapatite crystals deposit around collagen |
| Termination stage of bone remodeling | Osteoblasts become “trapped” in the mineralized matrix and mature into osteocytes |
| Osteoporosis | a disease of bone remodeling characterized by decreased bone mass; vulnerability to fractures |
| Mechanical stress | stress is detected by osteocytes, osteocytes communicate to osteoblasts, osteoblasts accelerate synthesis of osteoid and mineralization |
| Hormones | alter rates of osteoblast and/or osteoclast activity |
| How does estrogen affect bone remodeling? | estrogen stimulates osteoblast activity |
| How does calcitonin affect bone remodeling? | promotes calcium deposition in bone and inhibits osteoclast activity |
| What does bone remodeling play a critical role in? | regulating blood calcium |
| Hormones released when blood calcium levels are low | calcitriol, parathyroid hormone( PTH) |
| Hormones released when blood calcium levels are high | calitonin |
| How are blood calcium levels regulated through the parathyroid hormone and calcitriol | stimulus- low blood calcium, receptor- parathyroid glands (detect low blood calcium), control center- parathyroid glands release parathyroid hormone that stimulate the synthesis of calcitriol, effectors- bone, kidneys, and small intestines |
| How is bone an effector when regulating low blood calcium levels? | PTH and calcitriol increase osteoclast activity |
| How is the kidney an effector when regulating low blood calcium levels? | PTH and calcitriol decrease calcium excreted in urine |
| How is the small intestine an effector when regulating low blood calcium levels? | calcitriol increases calcium absorption from small intestines |
| Activation of calcitriol | upon exposure to UV radiation, keratinocytes synthesize vitamin D3 (cholecalciferol), vitamin D3 is converted to calcidiol in the liver and is then converted to calcitriol in the kidney |
| Regulation of high blood calcium levels | Stimulus- high blood calcium, receptor and control center- parafollicular cells in the thyroid glands, effector- inhibits osteoclast activity in bone, increases excretion of calcium from kidneys |
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kkade
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