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Osseous Tissue and Bone Structure

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Osseous Tissue and Bone Structure. BIOL241 “Lecture 6” (2 nd ) 3 rd Week INTERCONNECTEDNESS. Topics:. Skeletal cartilage Structure and function of bone tissues Types of bone cells Structures of the two main bone tissues Bone membranes Bone formation - PowerPoint PPT Presentation
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Osseous Tissue and Bone Structure BIOL241 “Lecture 6” (2 nd ) 3 rd Week INTERCONNECTEDNESS
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Page 1: Osseous Tissue  and Bone Structure

Osseous Tissue and Bone Structure

BIOL241 “Lecture 6”(2nd) 3rd Week

INTERCONNECTEDNESS

Page 2: Osseous Tissue  and Bone Structure

Topics:• Skeletal cartilage• Structure and function of bone tissues• Types of bone cells• Structures of the two main bone tissues• Bone membranes• Bone formation • Minerals, recycling, and remodeling• Hormones and nutrition• Fracture repair• The effects of aging

Page 3: Osseous Tissue  and Bone Structure

The Skeletal System• Skeletal system includes:

– bones of the skeleton– cartilages, ligaments, and connective tissues

Page 4: Osseous Tissue  and Bone Structure

Skeletal Cartilage• Contains no blood vessels or nerves• Surrounded by the perichondrium (dense

irregular connective tissue) that resists outward expansion

• Three types – hyaline, elastic, and fibrocartilage

Page 5: Osseous Tissue  and Bone Structure

Hyaline Cartilage• Provides support, flexibility, and resilience• Is the most abundant skeletal cartilage• Is present in these cartilages:

– Articular – covers the ends of long bones– Costal – connects the ribs to the sternum– Respiratory – makes up larynx, reinforces air

passages– Nasal – supports the nose

Page 6: Osseous Tissue  and Bone Structure

Elastic Cartilage• Similar to hyaline cartilage, but contains

elastic fibers• Found in the external ear and the epiglottis

Page 7: Osseous Tissue  and Bone Structure

Fibrocartilage• Highly compressed with great tensile

strength• Contains collagen fibers• Found in menisci of the knee and in

intervertebral discs

Page 8: Osseous Tissue  and Bone Structure

Growth of Cartilage• Appositional – cells in the perichondrium

secrete matrix against the external face of existing cartilage

• Interstitial – lacunae-bound chondrocytes inside the cartilage divide and secrete new matrix, expanding the cartilage from within

• Calcification of cartilage occurs– During normal bone growth– During old age

Page 9: Osseous Tissue  and Bone Structure

Bones and Cartilages of Homo sapiens

Figure 6.1

Page 10: Osseous Tissue  and Bone Structure

Functions of the Skeletal System

1. Support2. Storage of minerals (calcium)3. Storage of lipids (yellow marrow) 4. Blood cell production (red marrow)5. Protection6. Leverage (force of motion)

Page 11: Osseous Tissue  and Bone Structure

Bone (Osseous) Tissue

• Supportive connective tissue • Very dense• Contains specialized cells• Produces solid matrix of calcium salt

deposits and collagen fibers

Page 12: Osseous Tissue  and Bone Structure

Characteristics of Bone Tissue

• Dense matrix, containing:– deposits of calcium salts– osteocytes within lacunae organized

around blood vessels• Canaliculi:

– form pathways for blood vessels– exchange nutrients and wastes

Page 13: Osseous Tissue  and Bone Structure

Osteocyte and canaliculi

Page 14: Osseous Tissue  and Bone Structure

Characteristics of Bone Tissue

• Periosteum: – covers outer surfaces of bones – consist of outer fibrous and inner cellular

layers– Contains osteblasts responsible for bone

growth in thickness• Endosteum

– Covers inner surfaces of bones

Page 15: Osseous Tissue  and Bone Structure

Bone Matrix• Solid ground is made of mineral crystals• ⅔ of bone matrix is calcium phosphate,

Ca3(PO4)2:– reacts with calcium hydroxide, Ca(OH)2 to

form crystals of hydroxyapatite, Ca10(PO4)6(OH)2 which incorporates other calcium salts and ions

Page 16: Osseous Tissue  and Bone Structure

Hydroxyapatite

Page 17: Osseous Tissue  and Bone Structure

Bone Matrix• Matrix Proteins:

– ⅓ of bone matrix is protein fibers (collagen)

• Question: why aren’t bones made ENTIRELY of collagen if it’s so strong?

Page 18: Osseous Tissue  and Bone Structure

Bone Matrix• Mineral salts make bone rigid and

compression resistant but would be prone to shattering

• Collagen fibers add extra tensile strength but mostly add torsional flexibility to resist shattering

Page 19: Osseous Tissue  and Bone Structure

Chemical Composition of Bone: Organic

• Cells:– Osteoblasts – bone-forming cells– Osteocytes – mature bone cells– Osteoprogenitor cells – grandfather cells– Osteoclasts – large cells that resorb or break

down bone matrix• Osteoid – unmineralized bone matrix

composed of proteoglycans, glycoproteins, and collagen; becomes calcified later

Page 20: Osseous Tissue  and Bone Structure

The four major types of bone cells

in matrix only endosteum onlyperiosteum + endo

Page 21: Osseous Tissue  and Bone Structure

1. Osteoblasts • Immature bone cells

that secrete matrix compounds (osteogenesis)

• Eventually become surrounded by calcified bone and then they become osteocytes

Figure 6–3 (2 of 4)

Page 22: Osseous Tissue  and Bone Structure

2.Osteocytes

• Mature bone cells that maintain the bone matrix

Figure 6–3 (1 of 4)

Page 23: Osseous Tissue  and Bone Structure

Osteocytes

• Live in lacunae • Found between layers (lamellae) of matrix• Connected by cytoplasmic extensions through

canaliculi in lamellae (gap junctions)• Do not divide (remember G0?)• Maintain protein and mineral content of matrix• Help repair damaged bone

Page 24: Osseous Tissue  and Bone Structure

3. Osteoprogenitor Cells • Mesenchyme

stem cells that divide to produce osteoblasts

• Are located in inner, cellular layer of periosteum

• Assist in fracture repair

Page 25: Osseous Tissue  and Bone Structure

4. Osteoclasts

• Secrete acids and protein-digesting enzymes

Figure 6–3 (4 of 4)

Page 26: Osseous Tissue  and Bone Structure

Osteoclasts • Giant, mutlinucleate cells• Dissolve bone matrix and release stored

minerals (osteolysis)• Often found lining in endosteum lining the

marrow cavity • Are derived from stem cells that produce

macrophages

Page 27: Osseous Tissue  and Bone Structure

Homeostasis• Bone building (by osteocytes and -

blasts) and bone recycling (by osteoclasts) must balance:– more breakdown than building, bones

become weak– exercise causes osteocytes to build bone

Page 28: Osseous Tissue  and Bone Structure

Bone cell lineage summary• Osteoprogenitor cells

Osteoblasts

Osteocytes

• Osteoclasts are related to macrophages (blood cell derived)

Page 29: Osseous Tissue  and Bone Structure

Gross Anatomy of Bones: Bone Textures

• Compact bone – dense outer layer• Spongy bone – honeycomb of trabeculae

filled with yellow bone marrow

Page 30: Osseous Tissue  and Bone Structure

Compact Bone

Figure 6–5

Page 31: Osseous Tissue  and Bone Structure

Osteon• The basic structural unit of mature

compact bone• Osteon = Osteocytes arranged in

concentric lamellae around a central canal containing blood vessels– Lamella – weight-bearing, column-like matrix

tubes composed mainly of collagen

Page 32: Osseous Tissue  and Bone Structure

Three Lamellae Types

• Concentric Lamellae• Circumferential Lamellae

– Lamellae wrapped around the long bone line tree rings

– Binds inner osteons together• Interstitial Lamellae

– Found between the osteons made up of concentric lamella

– They are remnants of old osteons that have been partially digested and remodeled by osteoclast/osteoblast activity

Page 33: Osseous Tissue  and Bone Structure

Compact Bone

Figure 6–5

Page 34: Osseous Tissue  and Bone Structure

Microscopic Structure of Bone: Compact Bone

Figure 6.6a, b

Page 35: Osseous Tissue  and Bone Structure

Microscopic Structure of Bone: Compact Bone

Figure 6.6a

Page 36: Osseous Tissue  and Bone Structure

Microscopic Structure of Bone: Compact Bone

Figure 6.6b

Page 37: Osseous Tissue  and Bone Structure

Microscopic Structure of Bone: Compact Bone

Figure 6.6c

Page 38: Osseous Tissue  and Bone Structure

Spongy Bone

Figure 6–6

Page 39: Osseous Tissue  and Bone Structure

Spongy Bone Tissue• Makes up most of the bone tissue in short,

flat, and irregularly shaped bones, and the head (epiphysis) of long bones; also found in the narrow rim around the marrow cavity of the diaphysis of long bone

Page 40: Osseous Tissue  and Bone Structure

Spongy Bone• Does not have osteons• The matrix forms an open network of

trabeculae• Trabeculae have no blood vessels

Page 41: Osseous Tissue  and Bone Structure

Bone Marrow• The space between trabeculae is filled with

marrow which is highly vascular– Red bone marrow

• supplies nutrients to osteocytes in trabeculae• forms red and white blood cells

– Yellow bone marrow• yellow because it stores fat

• Question: Newborns have only red marrow. Red changes into yellow marrow in some bones as we age. Why?

Page 42: Osseous Tissue  and Bone Structure

Location of Hematopoietic Tissue (Red Marrow)

• In infants– Found in the medullary cavity and all areas of

spongy bone • In adults

– Found in the diploë of flat bones, and the head of the femur and humerus

Page 43: Osseous Tissue  and Bone Structure

Bone Membranes

• Periosteum – double-layered protective membrane– Covers all bones, except parts enclosed in joint

capsules (continuous w/ synovium)– Made up of:

• outer, fibrous layer (tissue?)• inner, cellular layer (osteogenic layer) is composed of

osteoblasts and osteoclasts– Secured to underlying bone by Sharpey’s fibers

• Endosteum – delicate membrane covering internal surfaces of bone

Page 44: Osseous Tissue  and Bone Structure

Sharpy’s (Perforating) Fibers• Collagen fibers of the outer fibrous layer of

periosteum, connect with collagen fibers in bone

• Also connect with fibers of joint capsules, attached tendons, and ligaments

• Tendons are “sewn” into bone via periosteum

Page 45: Osseous Tissue  and Bone Structure

Periosteum

Figure 6–8a

Page 46: Osseous Tissue  and Bone Structure

Functions of Periosteum1. Isolate bone from surrounding tissues2. Provide a route for circulatory and

nervous supply3. Participate in bone growth and repair

Page 47: Osseous Tissue  and Bone Structure

Endosteum

Figure 6–8b

Page 48: Osseous Tissue  and Bone Structure

Endosteum• An incomplete cellular layer:

– lines the marrow cavity– covers trabeculae of spongy bone– lines central canals

• Contains osteoblasts, osteoprogenitor cells, and osteoclasts

• Is active in bone growth and repair

Page 49: Osseous Tissue  and Bone Structure

Bone Development

• Human bones grow until about age 25• Osteogenesis:

– bone formation• Ossification:

– the process of replacing other tissues with bone• Osteogenesis and ossification lead to:

– The formation of the bony skeleton in embryos– Bone growth until early adulthood– Bone thickness, remodeling, and repair through life

Page 50: Osseous Tissue  and Bone Structure

Calcification• The process of depositing calcium salts • Occurs during bone ossification and in

other tissues

Page 51: Osseous Tissue  and Bone Structure

Formation of the Bony Skeleton

• Begins at week 8 of embryo development• Ossification

– Intramembranous ossification – bone develops from a fibrous membrane

– Endochondral ossification – bone forms by replacing hyaline cartilage

Page 52: Osseous Tissue  and Bone Structure

Intramembranous OssificationNote: you don’t have to know the steps of this process in

detail

• Also called dermal ossification (because it occurs in the dermis)– produces dermal bones such as mandible and

clavicle• Formation of most of the flat bones of the

skull and the clavicles• Fibrous connective tissue membranes are

formed by mesenchymal cells

Page 53: Osseous Tissue  and Bone Structure

The Genesis of Bone• When new bone is born, either during

development or regeneration, it often starts out as spongy bone (even if it will later be remodeled into compact bone)

Page 54: Osseous Tissue  and Bone Structure

Endochondral OssificationNote: you DO have to know this one

• Begins in the second month of development• Uses hyaline cartilage “bones” as models for

bone construction then ossifies cartilage into bone

• Common, as most bones originate as hyaline cartilage

• This is like a “trick” the body uses to allow long bones to grow in length when bones can only grow by appositional growth

Page 55: Osseous Tissue  and Bone Structure

Bone formation in a chick embryo

• Stained to represent hardened bone (red) and cartilage (blue)

• : This image is the cover illustration from The Atlas of Chick Development by Ruth Bellairs and Mark Osmond, published by Academic Press (New York) in 1998

Page 56: Osseous Tissue  and Bone Structure

Fetal Primary Ossification Centers

Figure 6.15

Page 57: Osseous Tissue  and Bone Structure

Stages of Endochondral Ossification

• Bone models form out of hyaline cartilage• Formation of bone collar• Cavitation of the hyaline cartilage• Invasion of internal cavities by the periosteal

bud, and spongy bone formation• Formation of the medullary cavity; appearance

of secondary ossification centers in the epiphyses

• Ossification of the epiphyses, with hyaline cartilage remaining only in the epiphyseal plates

Page 58: Osseous Tissue  and Bone Structure

Stages of Endochondral Ossification

Figure 6.8

Formation ofbone collararound hyalinecartilage model.

Hyalinecartilage

Cavitation ofthe hyaline carti-lage within thecartilage model.

Invasion ofinternal cavitiesby the periostealbud and spongybone formation.

Formation of themedullary cavity asossification continues;appearance of sec-ondary ossificationcenters in the epiphy-ses in preparationfor stage 5.

Ossification of theepiphyses; whencompleted, hyalinecartilage remains onlyin the epiphyseal platesand articular cartilages.

Deterioratingcartilagematrix

Epiphysealblood vessel

Spongyboneformation

Epiphysealplatecartilage

Secondaryossificatoncenter

Bloodvessel ofperiostealbud

Medullarycavity

Articularcartilage

Spongybone

Primaryossificationcenter

Bone collar

1

2

34

5

Page 59: Osseous Tissue  and Bone Structure

Endochondral Ossification: Step 1 (Bone Collar)

• Blood vessels grow around the edges of the cartilage

• Cells in the perichondrium change to osteoblasts: – producing a layer of

superficial bone (bone collar) around the shaft which will continue to grow and become compact bone (appositional growth)

Figure 6–9 (Step 2)

Page 60: Osseous Tissue  and Bone Structure

Endochondral Ossification: Step 2 (Cavitation)

• Chondrocytes in the center of the hyaline cartilage of each bone model:– enlarge– form struts and calcify– die, leaving cavities in cartilage

Figure 6–9 (Step 1)

Page 61: Osseous Tissue  and Bone Structure

Endochondral Ossification: Step 3 (Invasion)

• Periosteal bud brings blood vessels into the cartilage:– bringing osteoblasts and

osteoclasts– spongy bone develops at the

primary ossification center

Figure 6–9 (Step 3)

Page 62: Osseous Tissue  and Bone Structure

Endochondral Ossification: Step 4a (Remodeling)

Figure 6–9 (Step 4)

• Remodeling creates a marrow (medullary) cavity:– bone replaces cartilage at the

metaphyses– Diaphysis elongates

Page 63: Osseous Tissue  and Bone Structure

Endochondral Ossification: Step 4b (2° Ossification)

• Capillaries and osteoblasts enter the epiphyses:– creating secondary

ossification centers (perinatal)

Figure 6–9 (Step 5)

Page 64: Osseous Tissue  and Bone Structure

Endochondral Ossification: Step 5 (Elongation)

• Epiphyses fill with spongy bone but cartilage remains at two sites:– ends of bones within

the joint cavity = articular cartilage

– cartilage at the metaphysis = epiphyseal cartilage (plate)

Figure 6–9 (Step 6)

Page 65: Osseous Tissue  and Bone Structure

Postnatal Bone Growth• Growth in length of long bones

– Cartilage on the side of the epiphyseal plate closest to the epiphysis is relatively inactive

– Cartilage abutting the shaft of the bone organizes into a pattern that allows fast, efficient growth

– Cells of the epiphyseal plate proximal to the resting cartilage form three functionally different zones: growth, transformation, and osteogenic

Page 66: Osseous Tissue  and Bone Structure

Functional Zones in Long Bone Growth

• Growth zone – cartilage cells undergo mitosis, pushing the epiphysis away from the diaphysis

• Transformation zone – older cells enlarge, the matrix becomes calcified, cartilage cells die, and the matrix begins to deteriorate

• Osteogenic zone – new bone formation occurs

Page 67: Osseous Tissue  and Bone Structure

Growth in Length of Long Bone

Figure 6.9

Page 68: Osseous Tissue  and Bone Structure

Postnatal bone growth• Remember that bone growth can only

occur from the outside (appositional growth). So this type of endochondral growth is a way for bones to grow from the inside and lengthen because it is the cartilage that is growing, not the bone

Page 69: Osseous Tissue  and Bone Structure

Key Concept

• As epiphyseal cartilage grows through the division of chondrocytes it pushes the ends of the bone outward in length.

• At the “inner” (shaft) side of the epiphyseal plate, recently born cartilage gets turned into bone, but as long as the cartilage divides and extends as fast or faster than it gets turned into bone, the bone will grow longer

Page 70: Osseous Tissue  and Bone Structure

Long Bone Growth and Remodeling

• Growth in length – cartilage continually grows and is replaced by bone as shown

• Remodeling – bone is resorbed and added by appositional growth as shown – compact bone thickens and strengthens

long bones with layers of circumferential lamellae

Page 71: Osseous Tissue  and Bone Structure

Long Bone Growth and Remodeling

Figure 6.10

Page 72: Osseous Tissue  and Bone Structure

Appositional Growth

Page 73: Osseous Tissue  and Bone Structure

Epiphyseal Lines• When long bone stops growing, between the

ages of 18 – 25:– epiphyseal cartilage disappears – epiphyseal plate closes– visible on X-rays as an epiphyseal line

• At this point, bone has replaced all the cartilage and the bone can no longer grow in length

Page 74: Osseous Tissue  and Bone Structure

Epiphyseal Lines

Figure 6–10

Page 75: Osseous Tissue  and Bone Structure

• During infancy and childhood, epiphyseal plate activity is stimulated by growth hormone

• During puberty, testosterone and estrogens: – Initially promote adolescent growth spurts– Cause masculinization and feminization of

specific parts of the skeleton– Later induce epiphyseal plate closure, ending

long bone growth

Hormonal Regulation of Bone Growth During Youth

Page 76: Osseous Tissue  and Bone Structure

Remodeling• Remodeling continually recycles and

renews bone matrix• Turnover rate varies within and between

bones• If deposition is greater than removal,

bones get stronger• If removal is faster than replacement,

bones get weaker• Remodeling units – adjacent osteoblasts

and osteoclasts deposit and resorb bone at periosteal and endosteal surfaces

Page 77: Osseous Tissue  and Bone Structure

Bone Deposition• Occurs where bone is injured or added strength

is needed• Requires a diet rich in protein, vitamins C, D,

and A, calcium, phosphorus, magnesium, and manganese

• Alkaline phosphatase is essential for mineralization of bone

• Sites of new matrix deposition are revealed by the:– Osteoid seam – unmineralized band of bone matrix– Calcification front – abrupt transition zone between

the osteoid seam and the older mineralized bone

Page 78: Osseous Tissue  and Bone Structure

Effects of Exercise on Bone• Mineral recycling allows bones to adapt to

stress• Heavily stressed bones become thicker

and stronger

Page 79: Osseous Tissue  and Bone Structure

Response to Mechanical Stress

• Wolff’s law – a bone grows or remodels in response to the forces or demands placed upon it

• Observations supporting Wolff’s law include– Long bones are thickest midway along the shaft

(where bending stress is greatest)– Curved bones are thickest where they are most likely

to buckle• Trabeculae form along lines of stress• Large, bony projections occur where heavy,

active muscles attach

Page 80: Osseous Tissue  and Bone Structure

Response to Mechanical Stress

Figure 6.12

Page 81: Osseous Tissue  and Bone Structure

Bone Resorption

• Accomplished by osteoclasts• Resorption bays – grooves formed by

osteoclasts as they break down bone matrix• Resorption involves osteoclast secretion of:

– Lysosomal enzymes that digest organic matrix– Acids that convert calcium salts into soluble forms

• Dissolved matrix is transcytosed across the osteoclast cell where it is secreted into the interstitial fluid and then into the blood

Page 82: Osseous Tissue  and Bone Structure

Bone Degeneration• Bone degenerates quickly • Up to ⅓ of bone mass can be lost in a few

weeks of inactivity

Page 83: Osseous Tissue  and Bone Structure

Minerals, vitamins, and nutrients

Rewired for bone growth• A dietary source of calcium and phosphate

salts: – plus small amounts of magnesium, fluoride,

iron, and manganese• Protein, vitamins C, D, and A

Page 84: Osseous Tissue  and Bone Structure

Hormones for Bone Growth and Maintenance

Table 6–2

Page 85: Osseous Tissue  and Bone Structure

Calcitriol• The hormone calcitriol:

– synthesis requires vitamin D3 (cholecalciferol)– made in the kidneys (with help from the liver)– helps absorb calcium and phosphorus from

digestive tract

Page 86: Osseous Tissue  and Bone Structure

The Skeleton as Calcium Reserve• Bones store calcium and other minerals• Calcium is the most abundant mineral in the

body• Calcium ions in body fluids must be closely

regulated because:• Calcium ions are vital to:

– membranes– neurons– muscle cells, especially heart cells– blood clotting

Page 87: Osseous Tissue  and Bone Structure

Calcium Regulation: Hormonal Control

• Homeostasis is maintained by calcitonin and parathyroid hormone which control storage, absorption, and excretion

• Rising blood Ca2+ levels trigger the thyroid to release calcitonin

• Calcitonin stimulates calcium salt deposit in bone

• Falling blood Ca2+ levels signal the parathyroid glands to release PTH

• PTH signals osteoclasts to degrade bone matrix and release Ca2+ into the blood

Page 88: Osseous Tissue  and Bone Structure

Hormonal Control of Blood Ca

Figure 6.11

PTH;calcitoninsecreted

Calcitoninstimulatescalcium saltdepositin bone

Parathyroidglands releaseparathyroidhormone (PTH)

Thyroidgland

Thyroidgland

Parathyroidglands

Osteoclastsdegrade bonematrix and releaseCa2+ into blood

Falling bloodCa2+ levels

Rising bloodCa2+ levels

Calcium homeostasis of blood: 9–11 mg/100 ml

PTH

Imbalance

Imbalance

Page 89: Osseous Tissue  and Bone Structure

Calcitonin and Parathyroid Hormone Control

• Bones:– where calcium is stored

• Digestive tract:– where calcium is absorbed

• Kidneys:– where calcium is excreted

Page 90: Osseous Tissue  and Bone Structure

Parathyroid Hormone (PTH)• Produced by parathyroid glands in neck

• Increases calcium ion levels by:– stimulating osteoclasts – increasing intestinal absorption of calcium – decreases calcium excretion at kidneys

Page 91: Osseous Tissue  and Bone Structure

• Secreted by cells in the thyroid gland

• Decreases calcium ion levels by:– inhibiting osteoclast

activity– increasing calcium

excretion at kidneys

• Actually plays very small role in adults

Calcitonin

Page 92: Osseous Tissue  and Bone Structure

Fractures• Fractures:

– cracks or breaks in bones– caused by physical stress

• Fractures are repaired in 4 steps

Page 93: Osseous Tissue  and Bone Structure

Fracture Repair Step 1: Hematoma

• Hematoma formation– Torn blood vessels

hemorrhage– A mass of clotted blood

(hematoma) forms at the fracture site

– Site becomes swollen, painful, and inflamed

• Bone cells in the area die

Figure 6.13.1

Page 94: Osseous Tissue  and Bone Structure

Fracture Repair Step 2: Soft Callus• Cells of the endosteum and

periosteum divide and migrate into fracture zone

• Granulation tissue (soft callus) forms a few days after the fracture from fibroblasts and endothelium

• Fibrocartilaginous callus forms to stabilize fracture– external callus of hyaline

cartilage surrounds break– internal callus of cartilage

and collagen develops in marrow cavity

• Capillaries grow into the tissue and phagocytic cells begin cleaning debris

Figure 6.13.2

Page 95: Osseous Tissue  and Bone Structure

Stages in the Healing of a Bone Fracture

• The fibrocartilaginous callus forms when:– Osteoblasts and fibroblasts migrate to the

fracture and begin reconstructing the bone– Fibroblasts secrete collagen fibers that

connect broken bone ends– Osteoblasts begin forming spongy bone– Osteoblasts furthest from capillaries secrete

an externally bulging cartilaginous matrix that later calcifies

Page 96: Osseous Tissue  and Bone Structure

Fracture Repair Step 3: Bony Callus

• Bony callus formation– New spongy bone

trabeculae appear in the fibrocartilaginous callus

– Fibrocartilaginous callus converts into a bony (hard) callus

– Bone callus begins 3-4 weeks after injury, and continues until firm union is formed 2-3 months later

Figure 6.13.3

Page 97: Osseous Tissue  and Bone Structure

Fracture Repair Step 4: Remodeling

• Bone remodeling– Excess material on the bone

shaft exterior and in the medullary canal is removed

– Compact bone is laid down to reconstruct shaft walls

– Remodeling for up to a year• reduces bone callus• may never go away completely

– Usually heals stronger than surrounding bone

Figure 6.13.4

Page 98: Osseous Tissue  and Bone Structure

Clinical advances in bone repair• Electrical stimulation of fracture site.

– results in increased rapidity and completeness of bone healing– electrical field may prevent  parathyroid hormone from activating

osteoclasts at the  fracture site thereby increasing formation of bone and minimizing breakdown of bone,

• Ultrasound.  – Daily treatment results in decreased healing time of  fracture by

about 25% to 35% in broken arms and shinbones. Stimulates cartilage cells to make bony callus.

• Free vascular fibular graft technique. – Uses pieces of fibula to replace bone or splint two broken ends

of a bone.  Fibula is a non-essential bone, meaning it does not play a role in bearing weight; however, it does help stabilize the ankle.

• Bone substitutes.– synthetic material or crushed bones from cadavers serve as

bone fillers (Can also use sea coral).  

Page 99: Osseous Tissue  and Bone Structure

Aging and Bones• Bones become thinner and weaker with

age• Osteopenia begins between ages 30 and

40 • Women lose 8% of bone mass per

decade, men 3%• Can be induced by certain medications

Page 100: Osseous Tissue  and Bone Structure

Osteoporosis• Severe bone loss which affects normal function • Group of diseases in which bone reabsorption

outpaces bone deposit• The epiphyses, vertebrae, and jaws are most

affected, resulting in fragile limbs, reduction in height, tooth loss

• Occurs most often in postmenopausal women• Bones become so fragile that sneezing or

stepping off a curb can cause fractures• Over age 45, occurs in:

– 29% of women– 18% of men

Page 101: Osseous Tissue  and Bone Structure

Notice what happens in osteoporosis

Page 102: Osseous Tissue  and Bone Structure

Osteoporosis: Treatment• Calcium and vitamin D supplements• Increased weight-bearing exercise• Hormone (estrogen) replacement therapy

(HRT) slows bone loss• Natural progesterone cream prompts new

bone growth• Statins increase bone mineral density• PPIs may decrease density

Page 103: Osseous Tissue  and Bone Structure

Hormones and Bone Loss• Estrogens and androgens help maintain

bone mass• Bone loss in women accelerates after

menopause

Page 104: Osseous Tissue  and Bone Structure

Cancer and Bone Loss

• Cancerous tissues release osteoclast-activating factor:– stimulates osteoclasts– produces severe osteoporosis

Page 105: Osseous Tissue  and Bone Structure

Paget’s Disease• Characterized by excessive bone

formation and breakdown• An excessively high ratio of spongy to

compact bone is formed• Reduced mineralization causes spotty

weakening of bone• Osteoclast activity wanes, but osteoblast

activity continues to work

Page 106: Osseous Tissue  and Bone Structure

Developmental Aspects of Bones

• Mesoderm gives rise to embryonic mesenchymal cells, which produce membranes and cartilages that form the embryonic skeleton

• The embryonic skeleton ossifies in a predictable timetable that allows fetal age to be easily determined from sonograms

• At birth, most long bones are well ossified (except for their epiphyses)

Page 107: Osseous Tissue  and Bone Structure

Developmental Aspects of Bones

• By age 25, nearly all bones are completely ossified

• In old age, bone resorption predominates• A single gene that codes for vitamin D

docking determines both the tendency to accumulate bone mass early in life, and the risk for osteoporosis later in life

Page 108: Osseous Tissue  and Bone Structure

SUMMARY

• Skeletal cartilage• Structure and function of bone tissues• Types of bone cells• Structures of compact bone and spongy bone• Bone membranes, peri- and endosteum• Ossification: intramembranous and endochondral • Bone minerals, recycling, and remodeling• Hormones and nutrition• Fracture repair• The effects of aging

Page 109: Osseous Tissue  and Bone Structure

Figure 6–16 (1 of 9)

The Major Types of Fractures

• Simple (closed): bone end does not break the skin• Compound (open): bone end breaks through the skin• Nondisplaced – bone ends retain their normal position• Displaced – bone ends are out of normal alignment• Complete – bone is broken all the way through• Incomplete – bone is not broken all the way through• Linear – the fracture is parallel to the long axis of the

bone• Transverse – the fracture is perpendicular to the long

axis of the bone• Comminuted – bone fragments into three or more

pieces; common in the elderly

Page 110: Osseous Tissue  and Bone Structure

Types of fractures (just FYI)

Page 111: Osseous Tissue  and Bone Structure

More fractures


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