chapter bone histology
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Anatomy and Physiology
Bone HistologyBone HistologyLecture OutlineLecture Outline**
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Chapter 6Skeletal System:
Bones and Bone Tissue
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Skeletal System Functions
Support. Bone is hard and rigid; cartilage isflexible yet strong. Cartilage in nose, external ear,thoracic cage and trachea. Ligaments- bone to bone
Protection. Skull around brain; ribs, sternum,vertebrae protect organs of thoracic cavity
Movement. Produced by muscles on bones, viatendons. Ligaments allow some movement
between bones but prevent excessive movement Storage. Ca and P. Stored then released as
needed. Fat stored in marrow cavities
Blood cell production. Bone marrow that gives
rise to blood cells and platelets
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Components of Skeletal System Bone
Cartilage: three types
± Hyaline
± Fibrocartilage
± Elastic
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Hyaline Cartilage
Consists of specialized cells that produce matrix
± Chondroblasts: form matrix
± Chondrocytes: surrounded by matrix; are lacunae
Matrix. Collagen fibers for strength, proteoglycans for resiliency
Perichondrium. Double-layered C.T. sheath. Covers cartilage except atarticulations
± Inner. More delicate, has fewer fibers, contains chondroblasts
± Outer. Blood vessels and nerves penetrate. No blood vessels incartilage itself
Articular cartilage. Covers bones at joints; has no perichondrium Growth
± Appositional. New chondrocytes and new matrix at the periphery
± Interstitial. Chondrocytes within the tissue divide and add morematrix between the cells.
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Bone Shapes
Long
± Ex. Upper and lower
limbs
Short
± Ex. Carpals and tarsals
Flat
± Ex. Ribs, sternum,
skull, scapulae
Irregular
± Ex. Vertebrae, facial
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Long Bone
Structure
Diaphysis
± Shaft
± Compact bone Epiphysis
± End of the bone
± Cancellous bone
Epiphyseal plate: growth plate
± Hyaline cartilage; present until growthstops
Epiphyseal line: bone stops growing inlength
Medullary cavity: In children medullarycavity is red marrow, gradually changes toyellow in limb bones and skull (except for epiphyses of long bones). Rest of skeletonis red.
± Red marrow
± Yellow marrow
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Long Bone
Structure,
cont.
Periosteum
± Outer is fibrous
± Inner is single layer of bone cellsincluding osteoblasts, osteoclastsand osteochondral progenitor cells
± Fibers of tendon becomecontinuous with fibers of
periosteum. ± Sharpey¶s fibers: some periosteal
fibers penetrate through the periosteum and into the bone.Strengthen attachment of tendon to
bone.
Endosteum. Similar to inner layer of periosteum. Lines allinternal spaces including spaces
in cancellous bone.
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Flat, Short, Irregular Bones
Flat Bones
± No diaphyses, epiphyses
± Sandwich of cancellous between compact bone
Short and Irregular Bone
± Compact bone that surroundscancellous bone center; similar to structure of epiphyses of long bones
± No diaphyses and not
elongated Some flat and irregular
bones of skull have sinuseslined by mucous membranes.
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Bone Histology Bone matrix. Like reinforced concrete. Rebar is
collagen fibers, cement is hydroxyapetite ± Organic: collagen and proteoglycans
± Inorganic: hydroxyapetite. CaPO4 crystals
Bone cells (see following slides for particulars)
± Osteoblasts
± Osteocytes
± Osteoclasts
± Stem cells or osteochondral progenitor cells
Woven bone: collagen fibers randomly oriented
Lamellar bone: mature bone in sheets
Cancellous bone: trabeculae
C
ompact bone: dense
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Bone Matrix
If mineral removed, bone is too bendable
If collagen removed, bone is too brittle
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Bone Cells Osteoblasts
± Formation of bone through
ossification or osteogenesis.Collagen produced by E.R. and
golgi. Released by exocytosis.
Precursors of hydroxyapetite stored
in vesicles, then released byexocytosis.
± Ossification: formation of bone by
osteoblasts. Osteoblasts
communicate through gap
junctions. Cells surroundthemselves by matrix.
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Osteocytes
Osteocytes. Mature bonecells. Stellate. Surrounded
by matrix, but can makesmall amounts of matrix to
maintain it. ± Lacunae: spaces occupied by osteocyte cell body
± Canaliculi: canals occupied by osteocyte cell processes
± Nutrients diffuse through
tiny amount of liquidsurrounding cell and fillinglacunae and canaliculi.Then can transfer nutrientsfrom one cell to the nextthrough gap junctions.
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Osteoclasts and Stem Cells
Osteoclasts. Resorption of bone
± Ruffled border: where cell membrane borders bone andresorption is taking place.
± H ions pumped across membrane, acid forms, eatsaway bone.
± Release enzymes that digest the bone.
± Derived from monocytes (which are formed from stemcells in red bone marrow)
± Multinucleated and probably arise from fusion of anumber of cells
Stem Cells. Mesenchyme (OsteochondralProgenitor Cells) become chondroblasts or
osteoblasts.
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Woven and Lamellar Bone
Woven bone. Collagen fibers randomly oriented.
± Formed
During fetal development
During fracture repair
Remodeling
± Removing old bone and adding new
± Woven bone is remodeled into lamellar bone
L
amellar bone ± Mature bone in sheets called lamellae. Fibers areoriented in one direction in each layer, but in differentdirections in different layers for strength.
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Cancellous (Spongy) Bone
Trabeculae: interconnecting rods or plates of bone. Like
scaffolding. ± Spaces filled with marrow.
± Covered with endosteum.
± Oriented along stress lines
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Compact Bone
Central or Haversian canals: parallel to long axis
Lamellae: concentric,circumferential, interstitial
Osteon or Haversian system:
central canal, contents,associated concentric lamellaeand osteocytes
Perforating or Volkmann¶scanal: perpendicular to longaxis. Both perforating and
central canals contain bloodvessels. Direct flow of nutrientsfrom vessels through cell processes of osteoblasts andfrom one cell to the next.
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Compact
Bone
Osteons (Haversian
systems)
± Blood vessel-filled central
canal (Haversian canal)
± Concentric lamellae of bone
surround central canal
± Lacunae and canaliculi containosteocytes and fluid
Circumferential lamellae on
the periphery of a bone
Interstitial lamellae between
osteons. Remnants of osteons
replaced through remodeling
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Circulation in Bone
Perforating canals: bloodvessels from periosteum
penetrate bone
Vessels of the central
canal
Nutrients and wastestravel to and fromosteocytes via
± Interstitial fluid of lacunaeand canaliculi
± From osteocyte to osteocyte by gap junctions
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Bone Development: Two Types
Intramembranous ossification
± Takes place in connective tissue membrane
Endochondral ossification ± Takes place in cartilage
Both methods of ossification
± Produce woven bone that is then remodeled ± After remodeling, formation cannot be
distinguished as one or other
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Intramembranous Ossification Takes place in connective tissue membrane
formed from embryonic mesenchyme
Forms many skull bones, part of mandible,diaphyses of clavicles
When remodeled, indistinguishable fromendochondral bone.
Centers of ossification: locations in membranewhere ossification begins
Fontanels: large membrane-covered spaces between developing skull bones; unossified
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Intramembranous Ossification
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Endochondral Ossification Bones of the base of the skull, part of the
mandible, epiphyses of the clavicles, and
most of remaining bones of skeletal system Cartilage formation begins at end of fourth
week of development
Some ossification beginning at about week eight; some does not begin until 18-20 yearsof age
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Endochondral Ossification
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Endochondral Ossification
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Endochondral Ossification
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Growth in Bone Length
Appositional growth only
± Interstitial growth cannot occur because matrix is solid
± Occurs on old bone and/or on cartilage surface
Growth in length occurs at the epiphyseal plate Involves the formation of new cartilage by
± Interstitial cartilage growth
± Appositional growth on the surface of the cartilage
Closure of epiphyseal plate: epiphyseal plate isossified becoming the epiphyseal line. Between 12and 25 years of age
Articular cartilage: does not ossify, and persists
through life
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Zones of the Epiphyseal Plate
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Growth in Bone Length
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Growth at Articular Cartilage Increases size of bones with no epiphyses:
e.g., short bones
Chondrocytes near the surface of the
articular cartilage similar to those in zone of
resting cartilage
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Fracture of the Epiphyseal Plate
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Growth in Bone Width
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Factors Affecting Bone Growth
Size and shape of a bone determined genetically but can bemodified and influenced by nutrition and hormones
Nutrition ± Lack of calcium, protein and other nutrients during growth and
development can cause bones to be small
± Vitamin D Necessary for absorption of calcium from intestines
Can be eaten or manufactured in the body
Rickets: lack of vitamin D during childhood
Osteomalacia: lack of vitamin D during adulthood leading tosoftening of bones
± Vitamin C
Necessary for collagen synthesis by osteoblasts
Scurvy: deficiency of vitamin C
Lack of vitamin C also causes wounds not to heal, teeth to fallout
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Factors Affecting Bone Growth,
cont. Hormones
± Growth hormone from anterior pituitary. Stimulates
interstitial cartilage growth and appositional bonegrowth
± Thyroid hormone required for growth of all tissues
± Sex hormones such as estrogen and testosterone
Cause growth at puberty, but also cause closure of theepiphyseal plates and the cessation of growth
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Bone Remodeling
Converts woven bone into lamellar bone
Involved in bone growth, changes in bone shape, adjustments in bone dueto stress, bone repair, and Ca ionregulation
Relative thickness of bone changes as bone grows. Bone constantlyremoved by osteoclasts and new boneformed by osteoblasts.
Formation of new osteons in compact bone
± Osteoclasts enter the osteon from blood in the central canal andinternally remove lamellae.Osteoblasts replace bone
± Osteoclasts remove bone from theexterior and the bone is rebuilt
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Bone Repair 1. Hematoma formation. Localized mass of blood released from blood vessels butconfined within an organ or space. Clot
formation.2. Callus formation. Callus: mass of tissue
that forms at a fracture site and connects the broken ends of the bone.
± Internal- blood vessels grow into clot inhematoma.
Macrophages clean up debris, osteoclasts break down dead tissue, fibroblasts produce collagen and granulation tissue.
Chondroblasts from osteochondral progenitor cells of periosteum andendosteum produce cartilage within thecollagen.
Osteoblasts invade. New bone is formed.
± External- collar around opposing ends.Periosteal osteochondral progenitor cellsposteoblasts and chondroblasts.Bone/cartilage collar stabilizes two pieces.
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Bone Repair, cont.3. Callus ossification.
Callus replaced by
woven, cancellous bone
4. Bone remodeling.
Replacement of
cancellous bone and
damaged material by
compact bone. Sculptingof site by osteoclasts
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Calcium Homeostasis Bone is major storage site for calcium
The level of calcium in the blood depends
upon movement of calcium into or out of bone.
± Calcium enters bone when osteoblasts createnew bone; calcium leaves bone when
osteoclasts break down bone ± Two hormones control blood calcium levels-
parathyroid hormone and calcitonin.
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Calcium Homeostasis
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Effects of Aging on Skeletal System
Bone matrix decreases. More brittle due to lack of
collagen; but also less hydroxyapetite. Bone mass decreases. Highest around 30. Men
denser due to testosterone and greater weight.African Americans and Hispanics have higher
bone masses than Caucasians and Asians. Rate of bone loss increases 10 fold after menopause.Cancellous bone lost first, then compact.
Increased bone fractures
Bone loss causes deformity, loss of height, pain,stiffness
± Stooped posture
± Loss of teeth
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Bone
Fractures
Open (compound)- bone break with open wound. Bone may besticking out of wound.
Closed (simple)- Skin not perforated.
Incomplete- doesn¶t extend
across the bone. Complete- does Greenstick: incomplete fracture
that occurs on the convex side of the curve of a bone
Hairline: incomplete where two
sections of bone do not separate.Common in skull fractures
Comminuted fractures: completewith break into more than two
pieces
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Bone Fractures, cont.
Impacted fractures: onefragment is driven into thecancellous portion of theother fragment.
Classified on basis of
direction of fracture Linear
Transverse
Spiral
Oblique Dentate: rough, toothed,
broken ends
Stellate radiating out from acentral point.
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