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OSSEOUS TISSUE

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OSSEOUS TISSUE. SKELETAL STRUCTURE. Skeletal System. 206 bones, cartilage, ligaments, and connective tissues Functions: support provides a rigid framework storage calcium & phosphorus lipids production of blood cells formed in red marrow protection brain is encased in skull - PowerPoint PPT Presentation
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OSSEOUS TISSUE SKELETAL STRUCTURE
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Page 1: OSSEOUS TISSUE

OSSEOUS TISSUESKELETAL STRUCTURE

Page 2: OSSEOUS TISSUE

Skeletal System• 206 bones, cartilage, ligaments, and connective tissues • Functions: • support

– provides a rigid framework• storage

– calcium & phosphorus– lipids

• production of blood cells– formed in red marrow

• protection– brain is encased in skull– heart and lungs are surrounded by boney sternum and rib cage

• leverage– allows for movement due to interaction of muscular & skeletal

systems• acid-base balance

– absorbs or releases alkaline salts

Page 3: OSSEOUS TISSUE

Divisions of the Skeletal System• Axial skeleton

– consists of bones forming axis of the body– Skull– Hyoid– Sternum– Ribs– Vertebrae– sacrum & cocyx– auditory ossicles (not a part of either; but put here by

convention)• Appendicular skeleton

• consists of bones that anchor appendages to axial skeleton• upper & lower extremities, shoulder and pelvic girdles

Page 4: OSSEOUS TISSUE

Types of Bones

• Long• Flat• Short• Irregular• Sesamoid• Sutural

Page 5: OSSEOUS TISSUE

Long Bones• longer than wide• function as levers• act on skeletal

muscles to produce movements

• found in appendages

• fingers & toes

Page 6: OSSEOUS TISSUE

Short Bones• boxy & small• nearly cube-shape• found in wrist-carpals• ankle-tarsals• limited movements

Page 7: OSSEOUS TISSUE

Flat Bones• thin • roughly parallel surfaces• found in the roof of the

skull• sternum, ribs & scapula• enclose & protect soft

organs• provide broad surfaces for

muscle attachment

Page 8: OSSEOUS TISSUE

Irregular Bones• bones that do not fall into any other

category• varied, complex shapes, sizes & surface

features• vertebrae, sacrum, coccyx, temporal,

sphenoid, ethmoid, zygomatic, maxilla, mandible, palatine, inferior nasal concha, & hyoid

Page 9: OSSEOUS TISSUE

Sesamoid Bones• shaped like sesame

seeds develop in areas where there is a great deal of friction

• most only a few mms number in each person differs

• patella present in everyone

Page 10: OSSEOUS TISSUE

Sutural Bones• also called

Wormian bones• small• located in sutures • classified by

location-not by shape

Page 11: OSSEOUS TISSUE

Bone Composition• Osseous Tissue• supporting connective tissue• Composed of an extra cellular matrix and specialized cells

– give flexibility• two types• compact or dense bone

– dense, hard, & relatively solid– forms protective exterior of all bones

• spongy or cancellous bone– found inside most compact bone– very porous

• full of tiny holes forming open networks of struts & plates– lighter than compact bone

• reduces skeletal weight• makes it easier for muscles to move bones

Page 12: OSSEOUS TISSUE

Extracellular Matrix• composed of collagen fibers &

ground substance• hardened by inorganic calcium

phosphate deposits– called mineralization or

calcification• solid calcium phosphate salts

deposited around protein fibers• Calcium phosphate makes up 2/3rd

of bone weight• Calcium phosphate + calcium

hydroxide hydroxyapatite-Ca10(PO4)6(OH)2

• Calcium phosphate is hard, brittle & inflexible– can withstand compression

• Collagen fibers are stronger than steel, flexible- can be twisted & bent– not good at being compressed

• collagen makes a frame around which calcium minerals deposit

• combination makes bone flexible, strong & resistant to shattering

Page 13: OSSEOUS TISSUE

Bone Cell Types • Osteogenic cells– stem cells produce other

bone cells– found in cellular layer of

periosteum, endosteum & central canals

– continually divide– only bone cell that can divide

• Osteoblasts– bone-forming cells– make organic matter of

bone matrix• Osteocytes

– mature bone cells– most of bone cell population– former osteoblasts that have

become trapped in matrix they have deposited

• Osteoclasts– bone destroying cells

Page 14: OSSEOUS TISSUE

Osteocytes• cannot divide• function to maintain &

monitor protein & mineral content of matrix

• participate in bone repair by converting back into osteoblasts or osteogeneic cells at the site of injury

• sense strain & regulate bone remodeling

Page 15: OSSEOUS TISSUE

Osteoclasts• bone dissolving cells• function to remove bone by osteolysis • secrete acids & proteolytic enzymes

which degrade minerals & fibers and dissolve boney matrix

• releases matrix components into the blood restoring calcium and phosphorus concentrations in body fluids

Page 16: OSSEOUS TISSUE

Types of Bone Tissue• Compact Bone

– dense– covers exterior of all

bones• Spongy Bone

– cancellous– trabecular– inside compact bone– lighter

Page 17: OSSEOUS TISSUE

Compact Bone• basic functional unit -osteon or

Haversian system.• osteocytes are arranged in concentric

circles or layers-lamellae • around a central or Haversian canal

– runs parallel to surface– contains blood vessels

• perforating central canal are Volkmann’s canals

– run perpendicular to surface• canaliculi run through layers

– connect osteocytes to each other• interstitial lamellae fill spaces

between

Page 18: OSSEOUS TISSUE

Spongy Bone• matrix composition-

same• osteocytes, canalicui &

lamellae-different arrangements

• has no osteons • matrix forms plates or

struts called trabeculae (little beams)

• form a thin, branching open network filled with red bone marrow

• makes bone lighter

Page 19: OSSEOUS TISSUE

Bone Type & Bone Tissue Type Location

• the relationship between compact & spongy bone and the relative proportions of each varies with bone shape & with the function of the bone

Page 20: OSSEOUS TISSUE

Long Bone Structure• Diaphysis or shaft-long & cylindrical • Outside made of dense bone

– medullary canal or marrow cavity is filled with marrow

– Yellow bone marrow is dominated by fat cells & red marrow is responsible for forming blood cells

• Epiphysis-expanded extremities at either end of the bone– articulates with other bones-

forming joints– have broad surfaces for muscle

attachment. – filled with cancellous tissue

surrounded by thin layer of compact bone

• Metaphysis– connects diaphysis to epiphysis

Page 21: OSSEOUS TISSUE

Flat Bone Composition• function

– provide protection for underlying structures– broad surfaces for muscle attachment

• function can be seen by structure• resembles a spongy bone sandwich• composed of 2 thin layers of compact bone

covering a layer of spongy bone• bone marrow is present• there is no marrow cavity

Page 22: OSSEOUS TISSUE

Periosteum & Endosteum• Periosteum• covers all portions of compact bone

except at joint cavities• has fibrous outer layer & an inner

cellular layer• isolates bones from surrounding

tissues• provides route for blood vessels &

nerves• participates in bone growth & repair• continuous with other connective

tissues that mesh with-tendons & ligaments

• perforating or Sharpey’s fibers bond tendons & ligaments into the general structure of bone

• endosteum • consists of an incomplete cellular layer• lines marrow cavities• covers trabeculae of spongy bones • lines inner surfaces of central canals• active during bone growth, repair, and

remodeling

Page 23: OSSEOUS TISSUE

Blood & Nerve Supply • bone tissue is highly

vascular• Vessels pass into the

bone through the periosteum

• Periosteal arteries enter via perforating canals

• nutrient artery & vein• enter through a nutrient

foramen located in middle of the bone

Page 24: OSSEOUS TISSUE

Bone Growth• new bone matrix is made through

osteogenesis or ossification• process makes & releases

proteins & other organic components of matrix

• substance is osteoid–bone matrix before calcium salts

have been added• calcium salts are laid down in a

process called calcification

Page 25: OSSEOUS TISSUE

Bone Development & Growth• skeleton begins to form

at 6 weeks post fertilization

• does not stop until around age 25

• develops by two methods

• intramembranous ossification

• endochondral ossification

Page 26: OSSEOUS TISSUE

Intramembranous Ossification bone forms from

mesenchyme or fibrous connective tissue

produces flat bones of skull, most of the facial bones, mandible & medial part of the clavicle

bone develop within a fibrous sheet similar to dermis of the skin

bones are called dermal bones

Page 27: OSSEOUS TISSUE

Intramembranous Ossification Steps

• Step1: Development of Ossification Center

• Step 2: Calcification• Step 3: Formation of Trabeculae• Step 4: Development of

Periosteum

Page 28: OSSEOUS TISSUE

Step1: Development of Ossification Center

• at site where the bone is to form, chemical messages cause mesenchymal cells (embryonic connective tissue) to cluster together into a layer of soft tissue

• cells enlarge & differentiate into osteogenic cells and then into osteoblasts.

• site is the ossification center• osteoblasts begin to secrete

organic matrix• eventually become trapped &

become osteocytes

Page 29: OSSEOUS TISSUE

Step 2: Calcification• Calcium & other salts

deposit on organic extracellular matrix made by osteoblasts

• As trabeculae continue to grow calcium phosphate is deposited

• causes matrix to harden or calcify

Page 30: OSSEOUS TISSUE

Step 3: Formation of Trabeculae• osteoblasts

continue to deposit matrix

• continue to be calcified producing struts of trabeculae

• connective tissue present differentiates into red bone marrow

Page 31: OSSEOUS TISSUE

Step 4: Development of the Periosteum

• Mesenchyme condenses at periphery of the boneperiosteum.

• Trabeculae at surface continue to calcify until spaces between them are filled in converting spongy bone to compact bone

• process gives rise to sandwich like arrangement of flat bones

Page 32: OSSEOUS TISSUE

Intramembranous Ossification

Page 33: OSSEOUS TISSUE

Endochondral Ossification• bone forms by

replacing pre-existing hyaline cartilage model with bone

• most bones are made this way

• begins around sixth week of fetal development

• continues into the 20’s

Page 34: OSSEOUS TISSUE

Endochondral Ossification Steps• Step 1: Development of Hyaline Cartilage

Model• Step 2: Growth of Cartilage Model• Step 3: Development of Primary

Ossification Center• Step 4: Development of Medullary Cavity • Step 5: Development of Secondary

Ossification Centers• Step 6: Formation of Articular Cartilage &

Epiphseal Growth

Page 35: OSSEOUS TISSUE

Step 1: Development of Hyaline Cartilage Model

• at site when bone will form chemical messengers cause mesenchymal cells to crowed together in general shape of future bone

• cells develop into chondroblasts.

• begin to secrete cartilage extracellular matrix which develops into a hyaline cartilage bone covered with a perichondrium

Page 36: OSSEOUS TISSUE

Step 2: Growth of Cartilage Model

• once chondroblasts become embedded in extracellular matrix become chrondrocytes.

• cartilage model continues to grow longer from either end via interstitial or endogenous growth.

• grows in diameter or thickness via appositional or exogenous growth

– new cartilage is laid on the outside of model by chondroblasts

• as model continues to grow chondrocytes in area get larger in the mid-region area & the cartilage matrix begins to calcify

• enlarged chondrocytes are deprived of nutrients due to their size and calcification & diffusion cannot occur

• die and disintegrate• dying leaves spaces which merge into

small cavities called lacunae

Page 37: OSSEOUS TISSUE

Step 3: Development of Primary Ossification Center

• ossification continues inward from surface of bone to inside in the middle of model- primary ossification center

• a nutrient artery penetrates perichondrium

• stimulates osteogenic cells there to become osteoblasts

• once this occurs perichondrium is termed periosteum

• in the primary ossification center most of cartilage will be replaced with bone

• osteoblasts begin to deposit a thin collar of boney matrix around middle of cartilage model forming trabeculae of spongy bone

• primary ossification spreads from central area toward both ends of the cartilage model

Page 38: OSSEOUS TISSUE

Step 4: Development of Medullary Cavity

• as primary ossification center grows osteoclast cells break down some newly formed spongy bone trabeculae

• leaves a cavity• capillaries & fibroblasts migrate

to the inside of the cartilage and take over the spaces left by the dying chondrocytes

• as center is hollowed out & filled with blood and stem cells, it becomes primary marrow cavity.

• region of transition from cartilage to bone at the end of the primary marrow cavity is called the metaphysis

Page 39: OSSEOUS TISSUE

Step 5: Development of SecondaryOssification Centers

• when branches of the epiphyseal artery enter the epiphyses the secondary ossification centers form

• bone formation is similar to as described in the center of the bone

• here however spongy bone remains in the epiphyses

• secondary ossification proceeds outward from center of each epiphysis toward outer surface of the bone

Page 40: OSSEOUS TISSUE

Step 6: Formation of Articular Cartilage & Epiphseal Growth

• hyaline cartilage covering epiphyses develop into articular cartilages

• during infancy & childhood epiphyses fill with spongy bone

• cartilage is limited to articular cartilages

• prior to adulthood there is some hyaline cartilage that remains between the diaphysis and the epiphysis

• called epiphyseal or growth plate• area where bone will continue to

grow in length until it becomes adult sized

Page 41: OSSEOUS TISSUE

Endochondral Ossification

Page 42: OSSEOUS TISSUE

Endochondral Ossification

Page 43: OSSEOUS TISSUE

Bone Growth• bone increases in length & width• increases in length at epiphyseal

plate• interstitital growth• diameter of bone increases

through appositional growth• new tissues is deposited at

surface of the bone

Page 44: OSSEOUS TISSUE

Interstitital Growth• occurs at epiphyseal

plate• consists of hyaline

cartilage in middle with a transitional zone on either side

• in transitional zone cartilage is turning into bone

• epiphysis makes cartilage & ostoblasts try to overtake it by making bone

• osteoblasts cannot catch up bone gets longer

Page 45: OSSEOUS TISSUE

Interstitital Growth• epiphyseal plate

consists of four zones• zone of resting

cartilage• zone of proliferating

cartilage• zone of hypertrophic

cartilage• zone of calcified

cartilage

Page 46: OSSEOUS TISSUE

Interstitital Growth• In zone of resting cartilage small

chondrocytes present• do not participate in bone growth• cells anchor plate to the epiphysis• in zone of proliferating cartilage contains

slightly larger chondrocytes– undergo interstitial growth

• cells divide replacing those that die on diaphysis side of plate

• in zone of hypertrophy there are large, maturing chondrocytes arranged in columns

• zone of calcified cartilage contains few cells– cells are mostly dead due to extracellular matrix

around them having been calcified and no blood or nutrients can reach them

Page 47: OSSEOUS TISSUE

Interstitital Growth• at puberty rising

levels of sex & thyroid hormones cause osteoblasts to outpace manufacture of cartilage at epiphyseal end

• growth plate eventually fuses shut, leaving an epiphyseal line

• completes length of bone

Page 48: OSSEOUS TISSUE

Appositional Growth• way diameter of bone increases• new tissues is deposited at

surface of bone • at surface periosteal cells

differentiate into osteoblasts• begin to secrete organic parts of

matrix.• oteoid tissue is calcified• as osteoblasts become trapped

osteocytes• lay down matrix in layers parallel

to surface• produce circumferential lamellae

of bone

Page 49: OSSEOUS TISSUE

Bone Dynamics• bones constantly adapt to demands placed

on them and are continually remodeled throughout life

• part of normal growth & maintenance• 10% of skeleton tissue is replaced each year• organic and mineral components are

continuously recycled & removed through remodeling

• gives bone the ability to adapt to new stresses

Page 50: OSSEOUS TISSUE

Bone Dynamics• activities of both cells types are

continuous• activities must be balanced• when osteoclasts remove calcium

faster than osteoblasts can deposit itbone weakens

• when osteoblast activity predominates bones get stronger and more massive

Page 51: OSSEOUS TISSUE

Wolff’s law• bone’s structure is determined by mechanical stresses placed on it• one such stress is exercise• when bone is stressedmineral crystals generate small electrical

fields which attract osteoblasts• bony landmarks or bumps and ridges on surface of bone where

tendons attach may become more pronounced as muscles work to withstand increased forces

• regular exercise is needed to maintain normal bone structure• bone degeneration results from inactivity• changes in mineral content does not necessarily change shape of

bones because boney matrix contains protein fibers• bones can okay but may be soft due to no mineral deposition

– this is called osteomalacia• one form of this is rickets

– typically due to a vitamin D3 deficiency• not properly mineralized bones are flexible

– legs will bend under the weight of the body

Page 52: OSSEOUS TISSUE

Nutritional Needs• bone growth and maintenance requires

– calcium – phosphorous– magnesium– fluoride– manganese

• Calcitriol– from kidneys– absorption of calcium & phosphate from GI tract– synthesis of calcitriol depends on Vitamin D3

• therefore Vitamin D3 is needed for proper bone growth• Vitamin C

– needed for enzymatic reactions– needed for collagen synthesis– needed to stimulate osteoblast differentiation– without vitamin C there is a loss of bone strength and mass-scurvy

• Vitamin A– stimulates osteoblast activity– especially important for bone growth in children

• Vitamins K, and B12– needed for protein synthesis

Page 53: OSSEOUS TISSUE

Hormonal Needs• Growth hormone• Thyroxine• Sex hormones

–androgens in males–estrogens in females–help to close epiphyseal plates–stimulate osteoblasts to produce

bone at rate faster than epiphyseal cartilage can expand

Page 54: OSSEOUS TISSUE

Calcium Balance• most abundant mineral in the body• 90% is in bones• crucial to membrane functions• needed for activities of neurons & muscle

cells • for homeostatic balance three hormones

are needed• Calcitriol• Calcitonin• Parathyroid hormone

Page 55: OSSEOUS TISSUE

Calcitriol• active form of

vitamin D• principle

functionraise blood calcium

• increases absorption of calcium by small intestine

Page 56: OSSEOUS TISSUE

Calcitonin & Parathyroid Hormones

• opposite effects• Targets

–bones where calcium is stored–digestive tract where calcium is

absorbed–kidneys where calcium is

excreted

Page 57: OSSEOUS TISSUE

Calcitonin• made in thyroid gland• blood calcium levels rise

parafollicular or C cellsrelease calcitoninlowers blood calcium

• inhibits osteoclast activity slowing rate of calcium release from bone

• stimulates osteoblasts • encourages calcium to be

deposited into bones– more important during

childhood – also important in reducing loss

of bone mass during prolonged starvation & during late stages of pregnancy

– role in healthy adults is unknown

Page 58: OSSEOUS TISSUE

Parathyroid Hormone• made by parathryroid gland• calcium levels fall parathyroid

glandssecrete parathyroid hormone

• raises blood calcium levels– increases osteoclast acitivty

increases release of calcium from bones

– promotes calcium reabsorption by kidneys

– promotes final step of calcitriol synthesis in kidneys enhancing calcium uptake by intestine

– inhibits collagen synthesis by osteoblastscalcium deposition into bone decreases

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Calcium Balance


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