Chapter 6 Osseous Tissue and Skeletal Structure

8/13/2019 Chapter 6 Osseous Tissue and Skeletal Structure

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Osseous Tissue and Bone

Structure

Chapter 6


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Chapter Overview

1. Functions

2. A. Classification B. Structure C. Bone types

3. Bone tissue

A. Bone matrix

B. Bone cells

4. Bone StructureA. Compact

B. Spongy

5. Periosteum & Endosteum

6. Bone Formation and Growth7. Exercise, Hormones, and Nutrition

8. Calcium Homeostasis

9. Fractures

10. Osteopenia


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1. Skeletal System Functions

Skeletal system includes

Bones of the skeleton

Cartilages, ligaments, and connective tissues

5 Primary Functions: Support

Storage of minerals (calcium) & lipids (yellow marrow)

Blood cell production (red marrow- RBCs & WBCs)

Protection

Leverage (force of motion)


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2A. Classification of Bones

Bones are classified by

Shape

Internal tissue organization

Bone markings (surface features; marks)


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Long bonesLong and thin

Found in arms, legs,

hands, feet, fingers, toes

Flat bonesThin with parallel surfaces

Found in the skull,

sternum, ribs, scapulae


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c

Sutural bonesSmall, irregular bones

Found between the flat

bones of the skull

Irregular bonesHave complex shapes

Examples: spinal vertebrae,

pelvic bones


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c

c

c

c

Short bonesSmall and thick

Examples: ankle and wrist

bones

Sesamoid bonesSmall and flat

Develop inside tendons nearjoints of knees, hands, feet


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Bone Markings

Depressions or grooves

Along bone surface

Projections or elevations Where tendons and ligaments attach

At articulations with other bones

Tunnels

Where blood and nerves enter bone


9/70*You will learn these in lab! Not on your exam.


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*You will learn these in lab! Not on your exam.


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2B. Structure of a Long Bone

Diaphysis- the shaft

Heavy wall of compact bone

Central space- medullary (marrow)

cavity

Epiphysis- wide part at each end Articulation with other bones

Mostly spongy bone covered with

compact bone

Metaphysis

Where diaphysis & epiphysis meet


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2C. Bone Types

Compact (dense) bone Relatively solid

Surrounds medullary cavity (marrow cavity)

Makes up diaphysis

Cancellous (spongy or trabecular)

bone

Open network of struts & plates

Resembles lattice work with thin coveringof compact bone called the cortex (cortical

bone)

Red bone marrow, no medullary cavity


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Compact

Bone


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Spongy Bone

Diploe- in cranium, layer of spongy bone between cortex


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3. Bone (Osseous) Tissue

Supportive connective tissue

Dense connective tissue

Cartilage

Bone

Periosteum-covers outer surfaces of bones, except atjoints (outer fibrous& inner cellularlayers)

Contains specialized cells & matrix

Matrix- extracellular protein fibers & groundsubstance

Solid matrix- calcium salt deposits around collagen

fibers


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3A. Matrix of Bone

Matrix Minerals

2/3 bone matrix- calcium phosphate, Ca3(PO4)2

Reacts with calcium hydroxide, Ca(OH)2to form

crystals of hydroxyapatite

As crystals form- incorporate other calcium salts(calcium carbonate, CaCO3) and ions (magnesium,

sodium, fluoride)

Matrix Proteins

1/3 bone matrix- protein fibers (collagen)

*You do not need to memorize the molecular formula of the minerals

calcium phosphate + calcium hydroxide hydroxyapatite


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Bone Matrix

Strong as steel reinforced concrete! Calcium phosphate- hard, withstand

compression, but not bending/twisting

Collagen fibers- flexible, withstandbending/twisting, little resistance to

compression

Together- strong, somewhat

flexible, shatter resistance bone


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3B. Types of Bone Cells

Make up only 2% of bone

mass, bone mostly matrix

most abundant

builders

CanaliculiForm pathways for blood vesselsExchange nutrients and wastes


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Osteocytes

Mature bone cells that maintain the bone matrix

Each osteocyte occupies a lacuna

Lacunae- pocket between layers of matrix (lamellae)

Osteocytes do NOT divide!

Canaliculi(narrow passageways) penetrate

lamellae - radiate through matrix, connecting

lacunae & nutrient sources Cytoplasmic extensions of osteocytes occupy

canaliculi


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Osteocytes Functions

To maintain protein and mineral content of matrix

Bones are dynamic- constantly changing!

Break down matrix & build it back again

To help repair damaged bone

*Can

convert to

less

specialized

cell type ifreleased

from lacuna.


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Osteoblasts- immature bone cells

1. Osteogenesis- secrete organic bone matrix

Proteins, etc. before calcium salts are deposited

Osteoid- matrix produced by osteoblasts, not yet calcified

2. Elevate local concentrations of calcium phosphate

above solubility limit, triggers deposition of calciumsalts

Converts osetoid to bone

Osteoblasts surrounded bybone become osteocytes


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Types of Bone Cells

break down (crack)Stem cells

Osteoprogenitor cell

osteoblast osteocyte


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Osteoprogenitor Cells

Mesenchymal stem cells that divide to produceosteoblasts

Are located in endosteum, the inner, cellular

layer of periosteum

Assist in fracture

repair


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Osteoclasts

Giant, multinucleate cells remove & recycle bone

matrix

Derived from stem cells that produce macrophages

Secrete acids & protein-digesting enzymes dissolve

bone matrix & release stored minerals (osteolysis) Important in maintaining calcium and phosphate

concentrations in body fluids


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Maintaining Bone

Homeostasis: building = breakdown Bone building (osteoblasts) and bone recycling

(osteoclasts) must balance

More breakdown than building,bones become weak

Exercise, particularly weight-bearing

exercise, causes osteoblasts to

build bone


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4A. Structure of Compact Bone

Osteon-basic functional unit in mature compact bone Haversian System

Osteocytes are arranged in concentric lamellae

around a central canal containing blood vessels

Run parallel to bone surgafe

Perforating Canals- run perpendicular to central canal

Canals of Volkmann Carry blood vessels into deep bone and marrow


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Histology of Compact Bone


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Histology of Compact Bone


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4A. Structure of Compact Bone

Interstitial lamellae- fill spaces between osteons

in compact bone

Remnants of osteons whose matrix have almost been

entirely recycled by osteoclasts

Circumferential Lamellae

Lamellae on outter/inner bone surface, covered

by periosteum & endosteum respectively Produced during growth of bone


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Structure of Compact Bone


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Structure of Compact Bone

Force applied along the axis of

alignment- will not bend bone

(the weight of your body will

not break your femur)

Collagen fibers spiral- adds

strength & resiliency

Force applied suddensideways force to femur- break


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4B. Structure of Spongy Bone

No osteons- struts & plates called trabeculae

Trabeculae have no blood vessels

Nutrients diffuse along canaliculi

Lighter than compact bone

Withstand stresses from many different directions

Red bone marrow -fills space between trabeculae

Blood vessels, forms red blood cells

Supplies nutrients to osteocytes, removes wastes

Yellow marrow- stores fat


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Structure of Spongy Bone


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5. c

Periosteum- superficial layer of compact bone

(except joint cavities)

2 layers- outer fibrous layer, inner cellular layer

Functions-

Isolates bone from surrounding tissues Provides route for circulatory and nervous supply

Participates in bone growth and repair

Joints- periosteum becomes continuous with

connective tissues (joint capsule, tendons,

ligaments)

Perforating fibers-collagen fibers of the periosteum


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The Periosteum


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5. Periosteum & Endosteum

Endosteum lines the medullary cavity & covers

trabecullae of spongy bone

Incomplete cellular layer

Active in bone growth and repair

Contains osteoblasts, osteoprogenitor cells, and

osteoclasts


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The Endosteum


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6. Bone Formation and Growth

Human bones grow ~25 yrs old

Osteogenesis-bone formation

Ossification- process of replacing

other tissues with bone

Calcification-process of depositing

calcium salts Occurs during bone ossification

Can occur in other tissues


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Ossification

Two main forms of ossification

Endochondral ossification- bone replaces cartilage

Most bones originate as hyaline cartilage

Intramembranous ossification- bone develops directlyfrom mesenchyme or fibrous connective tissue

Dermal ossification- occurs in dermis

Produces dermal bones-mandible (lower jaw) and

clavicle (collarbone)


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Endochondral Ossification

-cartilage enlarges

-chondrocytes

increase in size

-lacunae expand

-matrix reduces tothin struts that begin

to calcify

-chondrocytes

deprived of nutrients-

no diffusion

-chondrocytes

become surrounded

by calcified cartilage,

die

-blood vessels

grow into

perichondrium

-inner layer cells

differentiate into

osteoblasts,

-osteoblasts

begin producingthin layer of

bone

-


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-blood vessels

penetrate cartilage,central region

-fibroblasts migrate

in, differentiate into

osteoblasts

-osteoblasts produce

spongy bone

(primary ossification

center)

-bone formationspreads along shaft

-remodelingcontinues as growth

occurs

-osteoclasts appear

& degrade

trabeculae in thecenter of diaphysis

(medullary cavity)

-growth continues in

length & diameter


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-centers of

epiphyses begin to

calcify

-capillaries,

osteoblasts migrate

in, (secondaryossification center)

-

-epiphysesbecome filled with

spongy bone

-articular cartilage

remains exposed

at joint cavity

-overtime reduces

to thin superficial

layer

-at metaphysis,

epiphyseal

cartilage

separates

epiphyses from

diaphysis


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Epiphyseal Lines


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Epiphyseal Lines

When long bone stops

growing, after puberty

epiphyseal cartilagedisappears

A i i l G h


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Appositional Growth

In early endochondral ossification, a superficial layer

of bone forms, then bone increase in diameter (outersurface)

Appositional Growth Cells of inner layer of periosteum differentiate into

osetoblasts, deposit superficial layers of bone matrix

Osteoblasts become surrounded by matrix- differentiate into

osteocytes Add series of layers form circumferential lamellae

I t b O ifi ti


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Intramembranous Ossification

-mesenchymal cells cluster

together and start secretingorganic components of matrix

-resulting osteoid becomes

mineralized as mesenchymal

cells differentiate intoosteoblasts

-developing bone grow

outward from ossification

center (where ossificationbegins) in spicules

-ossification trap osteoblasts,

differentiate into osteocyte

I t b O ifi ti


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-Blood vessels grow into

the area

-Spicules grow and fuse

together, trap blood vessels

within developing bone

I t b O ifi ti


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-Initially, intrmebraneous boneonly spongy bone

-Remodeling produce osteons

of compact bone

-Growth slows, periosteum

forms

-connetive tissue formsfibrous outer layer

-osteoblasts outer surface

become inner cellular layer

Bl d S l f M t B


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Blood Supply of Mature Bones

Bones very dynamic- constant remodeling

Three major sets of blood vessels develop

Nutrient artery and vein:

Single pair of large blood vessels, supply bood to diaphysis

Enter the diaphysis through the nutrient foramen during

endochondral ossification

Femur has more than one pair

Metaphyseal vessels:

Supply blood to the epiphyseal cartilage where bone growth

occurs

Periosteal vesselsprovide:

Blood to superficial osteons of the shaft

Blood to secondary ossification centers during endochondral

bone formation

Periosteum also contains


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Networks of lymphatic vessels

Sensory nerves

Bone injuries very painful!


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6 B R d li


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6. Bone Remodeling

Adult skeleton very dynamic- continually remodels,

recycles, and replaces

Replaces mineral reserves

Recycles and renews bone matrix

Involves osteocytes, osteoblasts, and osteoclasts Turnover rate varies

If deposition is greater than removal, bones get stronger

If removal is faster than replacement, bones get weaker

Store heavy metal ions in bone (lead, uranium,plutonium)

Cancer later in life as bone releases ions

7 E i Eff t B


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7. Exercise Effects on Bone

Bone is stressed, mineral crystals generate electrical

fields, attracts osteoblasts which produce bone

Mineral recycling allows bones to adapt to stress

Heavily stressed bones become thicker and stronger

Lifting weights highly beneficial

Bone Degeneration

Bone degenerates quickly

Up to one third of bone mass can be lost in a few weeks of

inactivity

Break leg, astronaut, paralyzed

7 H & N t iti l Eff t B


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7. Hormone & Nutritional Effects on Bone

Normal bone growth and maintenance requires nutritional

and hormonal factors Constant dietary source of calciumand phosphate salts

Small amounts of magnesium, fluoride, iron, manganese

Calcitriol-hormone made in the kidneys

Helps absorb calcium and phosphorus from digestive tract Synthesis requires vitamin D3(cholecalciferol)

Vitamin C- required for collagen synthesis, and stimulation of

osteoblast differentiation

Vitamin A- stimulates osteoblast activity

Vitamins K and B12help synthesize bone proteins

Calcitonin & parathyroid hormone regulate calcium &

phosphate levels

8 Calci m Homeostasis


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8. Calcium Homeostasis

Skeleton act as a calcium reserve

Bones store calcium and other minerals

Calcium is the most abundant mineral in the body

Calcium ionsare vital to:

Membranes & intracellular activities of neurons &muscle cells, especially heart cells

Too much calcium muscle & nerve cells unresponsive

Not enough calcium- neurons so excitable, convulsions50% reduction of calciumlead to death!

Calcium Homeostasis


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Calcium Homeostasis

Calcium tightly regulated in body

Calcitoninand parathyroid hormone

Control storage, absorption, and excretion

Calcitonin- thyroid gland

Parathyroid hormone- parathyroid gland Target

Bones- storage

Digestive tract- absorption

Kidneys- excretion

Calcium Homeostasis


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Calcium Homeostasis

Parathyroid Hormone (PTH)

Produced by parathyroid glands in neck

Increases calcium ion levels by

Stimulating osteoclasts, enhancing recycling of minerals by osteocytes

Increasing intestinal absorption of calcium

Decreasing calcium excretion at kidneys

Calcitonin

Secreted by C cells (parafollicular cells) in thyroid Decreases calcium ion levels by

Inhibiting osteoclast activity

Increasing calcium excretion at kidneys


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9 Fractures


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9. Fractures

Cracks or breaks in bones caused by physical stress

Major types of fractures:

Pott fracture- ankle, affects both bones

Comminuted fractures- shattered

Transverse fractures- break across access Spiral fractures- twisting stresses

Displaced fractures- abnormal bone arrangements

Colles fracture- break distal portion of radius

Greenstick fracture- 1 side of shaft broken, other bends

Epiphyseal fractures- where bone is undergoing calcification

Compression fractures- vertebrae under extreme stress


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-Extensive bleeding, large blood clot(fracture hematoma) closes off injured

-Cells of periosteum & endosteum rapiddivision & migrate in


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(fracture hematoma) closes off injured

vessels

-Establishes a fibrous network

-Bone cells in the area die

Fractures are repaired in 4 steps

division & migrate in

-External callus forms, stabalizes outer

edges

-Internal callus forms in medullary cavity

-Osteoblasts replace central cartilage ofexternal callus with spongy bone

-Cells continue remodeling ~1 yr


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external callus with spongy bone

-Struts of spongy bone unite broken ends

-Fragments of dead bone removed &

replaced

-Initially swelling

-Eventually calluses are removed

10 Osteopenia


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10. Osteopenia

Bones become thinner and weaker with age

Osteopenia-inadequate ossification

Begins between ages 30 and 40- osteoblast activity

drops, osteoclast activity remains constant

Women lose 8% of bone mass per decade, men 3%

Epiphyses, vertebrae, and jaws are most affected:

Resulting in fragile limbs

Reduction in height

Tooth loss

Osteoporosis- reduction in bone mass compromisesl f ti


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normal function

Severe bone loss & easily fractured

Over age 45, occurs in 29% of women,18% of men

Aging


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Aging

Hormones and Bone Loss

Estrogens and androgens help maintain bone mass

Bone loss in women accelerates after menopause

Cancer and Bone Loss

Cancerous tissues release osteoclast-activating

factor

Stimulates osteoclasts & produces severe

osteoporosis

Important Concepts


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Important Concepts

Skeletal functions

Bone shapes (dont need to memorize markings)

Bone structure

Difference between compact/spongy bone

Structure of each

What makes up bone matrix

Cell types/functions

Describe periosteum & endosteum

Important Concepts


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Important Concepts

Describe process of bone formation- endochondral

ossification & intramembranous ossification Describe how exercise affects bone formation

How do hormones/nutrients influence bone

formation

Describe calcium homeostasis by calcitonin and

parathyroid hormone

Describe how fractures are healed (do not need to

memorize fracture types)

Osteopenia/osteoporosis

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Chapter 6 Osseous Tissue and Skeletal Structure

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