chapter bone histology

8/8/2019 Chapter Bone Histology

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6-1

Anatomy and Physiology

Bone HistologyBone HistologyLecture OutlineLecture Outline**



6-2

Chapter 6Skeletal System:

Bones and Bone Tissue



6-3

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



6-4

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



6-7

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



6-8

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.



6-10

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



6-12

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.



6-13

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.



6-15

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



6-17

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.



6-18

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



6-19

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



6-20

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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6-27

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



6-28

Zones of the Epiphyseal Plate



6-29

Growth in Bone Length



6-30

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



6-31

Fracture of the Epiphyseal Plate



6-32

Growth in Bone Width



6-33

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



6-34

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



6-35

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.



6-37

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.



6-39

Calcium Homeostasis



6-40

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



6-41

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



6-42

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.

chapter bone histology

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