functions of bone rigid skeleton supports the body rigid skeleton supports the body provides sites...

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Functions of Bone Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of Provides sites for attachment of muscles and organs muscles and organs Protective cover for soft organs Protective cover for soft organs Hemopoiesis (marrow cavities) Hemopoiesis (marrow cavities) Reservoir for body’s calcium supply Reservoir for body’s calcium supply Calcium used for muscle contraction, Calcium used for muscle contraction, blood clotting, cell membrane blood clotting, cell membrane permeability, transmission of nerve permeability, transmission of nerve impulses impulses

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Page 1: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Functions of BoneFunctions of Bone

Rigid skeleton supports the bodyRigid skeleton supports the body Provides sites for attachment of Provides sites for attachment of

muscles and organsmuscles and organs Protective cover for soft organsProtective cover for soft organs Hemopoiesis (marrow cavities)Hemopoiesis (marrow cavities) Reservoir for body’s calcium supplyReservoir for body’s calcium supply

Calcium used for muscle contraction, Calcium used for muscle contraction, blood clotting, cell membrane blood clotting, cell membrane permeability, transmission of nerve permeability, transmission of nerve impulsesimpulses

Page 2: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

BoneBone

Connective tissue with a mineralized Connective tissue with a mineralized matrix (calcium phosphate)matrix (calcium phosphate)

Matrix is dense and rigid, contains Matrix is dense and rigid, contains fibers of mainly Type I collagen.fibers of mainly Type I collagen.

Both the collagen and the ground Both the collagen and the ground substance become mineralized in substance become mineralized in bone.bone.

Page 3: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Bone MatrixBone Matrix Calcified matrix of fibers (Type I collagen) and Calcified matrix of fibers (Type I collagen) and

ground substance (proteoglycans with chondroitin ground substance (proteoglycans with chondroitin sulfate and keratan sulfate side chains, sulfate and keratan sulfate side chains, glycoproteins)glycoproteins)

Organic component (osteoid)= type I collagen, Organic component (osteoid)= type I collagen, highly cross-linkedhighly cross-linked

Inorganic (mineral) component = crystals of Inorganic (mineral) component = crystals of calcium hydroxyapatite (calcium and phosphorus)calcium hydroxyapatite (calcium and phosphorus)

Hard – nutrients and metabolites cannot diffuse Hard – nutrients and metabolites cannot diffuse through the calcified matrix as done in cartilage.through the calcified matrix as done in cartilage.

Highly vascularized: Highly vascularized: Canaliculi –small channels or canals between lacunae that Canaliculi –small channels or canals between lacunae that

allow osteocytes to exchange wastes and bring metabolites allow osteocytes to exchange wastes and bring metabolites in; osteocytes send out cytoplasmic processes into the in; osteocytes send out cytoplasmic processes into the canaliculi and contact neighboring cells through gap canaliculi and contact neighboring cells through gap junctions.junctions.

Page 4: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Structure of Structure of BonesBones Diaphysis – shaftDiaphysis – shaft

Epiphysis – articular endsEpiphysis – articular ends

Periosteum – covers Periosteum – covers external surfaces;external surfaces;

- consists of an outer layer - consists of an outer layer of dense, irregular of dense, irregular collagenous (fibrous) CT collagenous (fibrous) CT and an inner layer of and an inner layer of osteoprogenitor and osteoprogenitor and osteoblast cellsosteoblast cells

Marrow – in central cavity Marrow – in central cavity of bone, hemopoietic of bone, hemopoietic tissue, red or yellowtissue, red or yellow

Page 5: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Epiphysis of an adult long bone

Compact boneSpongy (cancellous) bone

Compact bone

Page 6: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Spongy (Cancellous) BoneSpongy (Cancellous) Bone

- composed of spicules or trabeculae of bone;- forms network around bone marrow.

Page 7: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Compact BoneCompact Bone

-dense bone - no cavities;

-found along the outer surface of shafts of long bone.;

Page 8: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Compact bone has a lamellar structure

circumferential lamellae (on surfaces)

Haversian lamellae

interstitial lamellae.

Page 9: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Compact Bone – Low PowerCompact Bone – Low Powerhighly vascularizedhighly vascularized

Haversian canal

Volkmann’s canal

Haversian canal - the space running through an osteon; - contains blood vessels, nerves, osteoblasts and osteoprogenitor cells.

Volkmann’s canals – connect Haversian canals of adjacent osteons

Page 10: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Ground Bone – higher powerGround Bone – higher powercanaliculuscanaliculus

lacuna

Page 11: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Bone Bone MarroMarro

ww

fat cells

Blood-forming cells

Osteogenic (osteoprogenitor ) cells – line inner layer of endosteum

periosteum, and haversian canals; - undifferentiated stem cells that give rise to osteoblasts

Page 12: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Bone Formation – 2 typesBone Formation – 2 types

Intramembranous ossification – Intramembranous ossification – formation of bone directly from formation of bone directly from mesenchyme (embryonic CT) with no mesenchyme (embryonic CT) with no cartilage precursorcartilage precursor

Endochondral – formation of bone on Endochondral – formation of bone on cartilage cartilage

scaffolding; scaffolding;

- bone eventually replaces cartilage.- bone eventually replaces cartilage.

Page 13: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

IntramembranousOssification

Occurs in flat bones of skull, mandible,

maxilla.

Osteoblasts develop from CT mesenchyme cells.

Osteoblasts secrete osteoid (uncalcified bone matrix).

Page 14: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Intramembranous Intramembranous OssificationOssification

osteoblasts

Bone matrix is first formed as a network of spicules or trabeculae.

Osteoblasts – immature bone cells; - - secrete osteoid (uncalcified bone matrix

Osteocytes – mature bone cells; trapped within lacunae of bone matrix

osteocytes

Page 15: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Osteoclasts – large, multinucleate cells; - at the surfaces of bone - resorb & remodel bone in response to hormone and calcium levels

Howships lacunae – depressions made by osteoclasts as they etch away the bone.

Bones are dynamic structures! Bones are dynamic structures! Continually Continually being remodeledbeing remodeled

Page 16: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Osteoclast activity is regulated by Osteoclast activity is regulated by hormoneshormones

Parathyroid hormoneParathyroid hormone – increases blood – increases blood calcium levels; calcium levels; stimulates activity of stimulates activity of osteoclasts and osteoclasts and increases their increases their numbers.numbers.

CalcitoninCalcitonin (from (from thyroid gland) – thyroid gland) – decreases blood decreases blood calcium levels; calcium levels; reduces the numbers reduces the numbers and activity of and activity of osteoclasts.osteoclasts.

Page 17: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Endochondral Ossification

Occurs in long and short bones, Occurs in long and short bones, vertebraevertebrae

Bone is proceeded by temporary Bone is proceeded by temporary hyaline cartilage model that serves as a hyaline cartilage model that serves as a structural scaffold.structural scaffold.

Bone tissue REPLACES the cartilageBone tissue REPLACES the cartilage

Cartilage begins to calcify and causes Cartilage begins to calcify and causes chondrocytes to hypertrophy.chondrocytes to hypertrophy.

Cartilage calcifies so diffusion of Cartilage calcifies so diffusion of nutrients to chondrocytes stops and nutrients to chondrocytes stops and they die.they die.

Fragmented pieces of calcified Fragmented pieces of calcified cartilage serve as the framework to cartilage serve as the framework to deposit the bone.deposit the bone.

Osetoprogenitor cells and blood vessels Osetoprogenitor cells and blood vessels from surrounding connective tissue from surrounding connective tissue penetrate and invade degenerating penetrate and invade degenerating cartilage model.cartilage model.

Cartilage of diaphysis replaced by bone Cartilage of diaphysis replaced by bone except for at epiphyseal plate.except for at epiphyseal plate.

Page 18: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Endochondral Ossification – bone Endochondral Ossification – bone replaces a cartilage modelreplaces a cartilage model

cartilage

bone

Page 19: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Endochondral Ossification

cartilage

bone replacing cartilage

Page 20: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

EndochonEndochondral dral

OssificatioOssificationn

bone replacing cartilage

Page 21: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Summary of Bone Cell Types

Page 22: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Primary vs. Secondary BonePrimary vs. Secondary Bone

Primary – immature or “woven” Primary – immature or “woven” bonebone First bone formed in fetal First bone formed in fetal

development or bone repairdevelopment or bone repair Abundant osteocytesAbundant osteocytes Irregular bundles of collagen (Type I)Irregular bundles of collagen (Type I)

Secondary Secondary bone – bone – mature or mature or lamellar lamellar bonebone

Page 23: Functions of Bone Rigid skeleton supports the body Rigid skeleton supports the body Provides sites for attachment of muscles and organs Provides sites

Methods to Make Slides Methods to Make Slides of Boneof Bone

Decalcified bone sectionsDecalcified bone sections Acid solution removes calcium salts and softens Acid solution removes calcium salts and softens

bone.bone. Bone can then be embedded and sectioned.Bone can then be embedded and sectioned. Osteocytes are distorted.Osteocytes are distorted.

Ground bone sectionsGround bone sections Saw bone in slices.Saw bone in slices. Grind piece down until thin enough to put on a Grind piece down until thin enough to put on a

slide.slide. Cells are destroyed and lacunae and canaliculi Cells are destroyed and lacunae and canaliculi

filled with bone debris.filled with bone debris.