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Human Anatomy

Cartilage and Bone Connective Tissue

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General Osteology /ArthrologyDefinitions:

Osteology: the study of bonesBones: organs of the skeletal system

Skeletal System: bones and associated cartilagesArthrology: the study of joints

Point of movement (fulcrum)Endoskeleton: internal skeleton

endo- = insideVersus exoskeleton

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Skeletal SystemComposed of dynamic living tissues

Osseous tissue, cartilage, fibrous CT, blood, nervous tissue.

Continually rebuilds and remodels itselfChanges over a lifetime

Interacts with all of the other organ systems.Includes:

bones of the skeletonCartilageLigamentsother connective tissues that stabilize or connect the bones.

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Skeletal SystemFunctions:

Supports our weight. Interacts with muscles to produce movements. ProtectionBlood cell formation

Red bone marrowMineral storage

Calciumphosphate

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Cartilage Connective TissueCharacteristics:

Weaker than boneMore flexible than bone

Cells in an abundant matrix. Cell Types

ChondroblastsChondrocytes in lacunae

Avascular

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3 Major Functions of CartilageSupporting soft tissues.Providing a gliding surface at articulations (joints)Providing a model for the formation of most of the bones in the body.

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Types of Cartilage Three types of cartilage:

Hyaline cartilageMost abundant kindHas a perichondrium (membrane)Associated with synovial jointsMost bones first modeled in hyaline cartilage

FibrocartilageHas collagen fibersIntervertebral discs, pubic symphysis

Elastic cartilage Has elastic fibersEar, respiratory tubing

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Growth Patterns of Cartilage Two main types:

Interstitial GrowthAppositional Growth.

Interstitial Growth. Chondrocytes in lacuna undergoes mitosis. Two chondrocytes in one lacunaWill push apart, form separate lacuna

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Growth Patterns of Cartilage Appositional Growth.

Undifferentiated cells divide (mitosis)One daughter cell remains a stem cell, one differentiates into a committed cell. Committed cell further differentiates into chondroblastLocated at edge of cartilage

Both types common during growthLater, mostly appositionalIn adult, usually no growth unless for repair

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Bone

Bones are organsBones are composed of all tissue types. Their primary component is osseous connective tissue. The matrix is sturdy and rigid due to calcification (also called mineralization).

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Functions of BoneSupport. Protection. MovementHemopoiesisStorage of minerals. Energy Reserves (marrow)

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Support and Protection

Bones provide structural support and serve as a framework for the entire body. Bones protect many delicate tissues and organs from injury and trauma.

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Movement Muscles attach to the bones of the skeleton

contract and pull on bonefunctions as a series of levers.

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Hemopoiesis

Blood cell production in red bone marrow

located in some spongy bone.

Red bone marrow contains stem cellsform all of the blood cell types.

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Storage of Mineral and Energy Reserves

More than 90% of the body’s reserves of the minerals calcium and phosphate are stored and released by bone.

Calcium: needed formuscle contractionblood clottingnerve impulse transmission.

Phosphate: needed forATP utilization structure of nucleic acids (DNA, RNA)

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Classification of Bone by Organization

AxialSkullVertebral columnThorax

Sternumribs

AppendicularPectoral

Girdleappendage

Pelvic Girdleappendage

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Classification of Bone by Shape

LongShortFlatIrregular

Surface features vary

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Structure of Long BoneDiaphysisEpiphysis

proximaldistal

MetaphysisEpiphyseal lineArticular cartilageMedullary cavity

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Structure of Long BoneEndostium: lines marrow cavity, incomplete

Osteoprogenitor cellsOsteoblastsOsteoclasts

Periostium: covers bone everywhere but articular surfaces

Two layersFibrous layer: outermost, dense irregular CT

Site of tendon attachmentInner layer: next to compact bone

Osteoblasts present in young bone

Anchored to bone by perforating fibers (collagen)

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Flat Bones of the SkullTwo layers of compact bone

Inner tableOuter table

Region of spongy bone sandwiched between them

Called the diploe Both layers of compact bone are covered by periosteum

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Four Types of Bone CellsOsteoprogenitor cells

stem cells derived from mesenchyme which produce other stem cells and osteoblasts

Osteoblastsproduce new bone, and once osteoblasts become entrapped in the matrix they produce and secrete, they differentiate into osteocytes

Osteocytesmature bone cells

Osteoclasts: not derived form osteoprogenitorsRelated to macrophagesFormed from multiple cells; are multinucleatedare involved in bone resorption

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OsteoclastsLocated in Howship’s lacunaRuffled edge contacts boneSecrete hydrochloric acid

Dissolves mineralsosteolysis

LysosomesSecrete enzymes that dissolve matrix

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Composition of Bone MatrixOrganic components: one third

CellsCollagen fibersGround substance

Inorganic components: two thirdsCalcium phosphateHydroxyapatite crystals: calcium phosphate and calcium hydroxide

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Types of Osseous TissueCompact

Dense, cortical

SpongyCancellous, trabecular

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Compact Bone MicroanatomyOsteon (Haversian) system: basic unit

Central (Haversian) canalConcentric lamellae

Contain collagen fibersOsteocytesLacunaeCanaliculi: permit intercellular communication

Cylinder that runs with long axis of long bone

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Compact Bone MicroanatomyPerforating canals (Volkmann canals)

Contain blood vessels, nerveRun perpendicular to central canals, connect them

Circumferential lamellaeInternal to periostium

External circumferential lamellaeInternal to endosteum

Internal circumferential lamellaeRun the entire circumference

Interstitial lamellaeRemains of osteons

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Spongy Bone MicroanatomyNo osteonsIn trabeculae:

Parallel lamellaeOsteocytes in lacunaecanaliculi

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OssificationOsteogenesis: bone formation and developmentBegins in the embryo: By the eighth through twelfth weeks:

the skeleton begins forming:from mesenchymeor from a hyaline cartilage model of bone.

These models are replaced by hard bone

Continues during childhood and adolescence.In the adult, ossification continues.

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Intramembranous Ossification Also called dermal ossificationProduces:

the flat bones of the skull (cranial vault)some of the facial bones (zygomatic bone, maxilla), the mandible (lower jaw)the central part of the clavicle (collarbone).

It begins when mesenchyme becomes thickened and condensed with a dense supply of blood capillaries.

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Intramembranous Ossification

1. Ossification centers form in thickened mesenchyme

Osteoprogenitors develop, become osteoblasts

2. Osteoid (bone matrix) calcifies

Trapped osteoblastsbecome osteocytes

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Intramembranous Ossification

3. Woven bone (primary bone) forms, periostium forms (from mesenchyme)

4. Lamellar bone(secondary bone) replaces woven bone; compact and spongy bone form

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Endochondral Ossification

Begins with a hyaline cartilage modelProduces most of the other bones of the skeletonLong bone will be used as an example.

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Endochondral OssificationSteps:1. Cartilage model develops:

Chondroblasts become chondrocytesPerichondrium develops

2. Cartilage calcification, bone collar develops in shaft

Chondrocytes hypertrophy, then dieBlood vessels grow toward cartilageOsteoblasts under perichondrium form bone

3. Primary Ossification center forms:Periosteal bud: osteoblasts and blood vessels12th week: most have formed

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Endochondral Ossification

Steps:3. Secondary Ossification centers:

In epiphysisSome form post-natally

4. Cartilage replaced by boneExcept articular cartilage, epiphyseal plate

5. Epiphyseal plate ossifies:Forms epiphyseal lineBetween 10 and 25Last… clavicle

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Epiphyseal Plate MorphologyHyaline cartilage5 zones: from epiphysis to diaphysisZone of resting cartilage

Small chondrocytes in cartilage matrixLooks like healthy cartilageSecures epiphyseal plate to epiphysis

Zone of proliferating cartilageChondrocytes here are undergoing rapid mitosisStack up in columns

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Epiphyseal Plate MorphologyZone of hypertrophic cartilage

Chondrocytes stop dividingStart hypertrophyAbsorb matrix

Zone of calcified cartilageFew cells thickCalcification of matrixKills the chondrocytes

Zone of ossificationInvasion by capillaries and osteoprogenitor cells

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Bone GrowthInterstitial growth occurs in the epiphyseal plate as chondrocytes undergo mitosis

Growth in length

Appositional growth occurs within the periosteum.

Growth in diameter, thickness

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Bone Remodeling The continual deposition of new bone tissue and the removal (resorption) of old bone tissue.

helps maintain calcium and phosphate levels in body fluids, and can be stimulated by stress on a bone occurs at both the periosteal and endosteal surfaces of a bone

Relative rates differ with age, bone

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Blood Supply and Innervation Bone is highly vascularized, especially in regions containing red bone marrow. Kinds of blood vessels

Nutrient artery and the nutrient veinsupply the diaphysis of a long bone

Metaphyseal blood vesselsDiaphyseal face of epiphyseal plate

Periosteal blood vesselsSupply superficial osteons on diaphysis.

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Effects of Hormones Control and regulate growth patterns in bone by altering the rates of both osteoblast and osteoclast activity. Growth hormone (Pituitary gland): affects bone growth by stimulating the formation of another hormone, somatomedin which is produced by the liver. Somatomedin: directly stimulates growth of cartilage in the epiphyseal plate.

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Effects of HormonesThyroid hormone (Thyroid gland): stimulates bone growth. Growth hormone and thyroid hormone regulate and maintain normal activity at the epiphyseal plates until puberty. Calcitonin (Thyroid gland): inhibits osteoclast activity. Parathyroid Hormone (Parathyroid gland): increases blood calcium levels, stimulates osteoclast activitySex Hormones: gonads

Increase rate of bone formationProduction associated with puberty

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Effects of VitaminsVitamin A: activates osteoblastsVitamin C: normal synthesis of collagenVitamin D: absorption and transport of calcium and phosphate

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