Bone Tissues 1

8/2/2019 Bone Tissues 1

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Bone Tissue: Specialized Connective Tissue

Cells

Fibers

Extracellular Matrix


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Bone Tissue: Specialized Connective Tissue

Extracellular Matrix

25% Water

25% Protein or organic matrix

95% Collagen Fibers

5% Chondroitin Sulfate

50% Crystalized Mineral Salts

Hydroxyapatite

(Calcium Phosphate)


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Two Kinds of Bone

Compact Bone

Spongy Bone


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Histology of Bone Tissue


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Histology of Compact Bone

Osteon is concentric rings (lamellae) of calcified matrixsurrounding a vertically oriented blood vessel

Osteocytes are found in spaces called lacunae Osteocytes communicate through canaliculi filled with

extracellular fluid that connect one cell to the next cell

Interstitial lamellae represent older osteons that have beenpartially removed during tissue remodeling


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Compact Bone


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The Trabeculae of Spongy Bone

Latticework of thin plates of bone called trabeculae orientedalong lines of stress

Spaces in between these struts are filled with red marrowwhere blood cells develop

Found in ends of long bones and inside flat bones such as thehipbones, sternum, sides of skull, and ribs.

No true Osteons.


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Spongy Bone

Spongy (cancellous) bone does notcontain osteons. It consists of trabeculae

surrounding many red marrow filled

spaces (Figure 6.3b). It forms most of the structure of short,

flat, and irregular bones, and the

epiphyses of long bones.

Spongy bone tissue is light and supportsand protects the red bone marrow.


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Compact vs. spongy bone

Compact bone External layer Arranged in osteons Lamellae are found

around periphery and

between osteons

Central canalsconnected to eachother by perforating

canals

Spongy bone No osteons Arranged in

trabeculae

Major type of tissuein short, flat,

irregular bones

Much lighter thancompact bone Supports red bone

marrow


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BONE FORMATION

All embryonic connective tissue begins as mesenchyme. Bone formation is termed osteogenesis or ossification

and begins when mesenchymal cells provide the

template for subsequent ossification.

Two types of ossification occur.Intramembranous ossification is the formation of

bone directly from or within fibrous connective

tissue membranes.

Endochondral ossification is the formation of bonefrom hyaline cartilage models.


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Two Kinds of

Ossification1. Intramembranous

Ossification

2. Endochondral

Ossification


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Intramembranous Ossification

Also called dermal ossification because it

normally occurs in the deeper layers of

connective tissue of the dermis of the skin.

All roofing bones of the SkullFrontal bone

Parietal bones

Occipital bone

Temporal bones Mandible Clavicle


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Intramembranous Ossification


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Centers of Ossification

Centers of Ossification


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Endochondral Ossification

Developing bones are deposited as a hyaline

cartilage model and then this cartilage is

replaced by bone tissue.

All bones of the body except: All roofing bones of the Skull Mandible Clavicle


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Endochondral ossification

Most bones are formedthis way

Calcification istriggered whenchondrocytes die

Vascularization triggersossification


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Bone growth in length (epiphyseal

plate)

Growth is on epiphysealside

Resting cartilage securesepiphyseal plate

Dividing cells are inproliferating cartilage

Cells mature in hypertrophiccartilage

Osteoblasts replace calcifiedcartilage


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Bones get thicker by appositional

growth

Osteoblasts form newextracellular matrix

Blood vessel becomesenclosed, supports new

osteon

Osteoblasts lay downextracellular matrix


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Growth at epiphyseal

plates

Zones of epiphyseal plates

Zone of Resting Cartilage

Zone of Proliferating Cartilage

Zone of Hypertrophic Cartilage

Zone of Calcified Cartilage


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Zones of Growth in

Epiphyseal Plate

Zone of resting cartilage anchors growth plate to bone

Zone of proliferating cartilage rapid cell division (stacked coins)

Zone of hypertrophic cartilage cells enlarged & remain in

columns

Zone of calcified cartilage thin zone, cells mostly dead since

matrix calcified

osteoclasts removing matrix osteoblasts & capillaries move into create bone over calcified

cartilage


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Growth at epiphyseal plates



Zone of ProliferatingCartilage

Zone of Hypertrophic

Cartilage



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Zone of Proliferating

Cartilage


Cartilage




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Cartilage


Cartilage




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Cartilage


Cartilage




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Growth in Thickness

Bone can grow in thickness or diameter only byappositional growth.

The steps in these process are: Periosteal cells differentiate into osteoblasts which

secrete collagen fibers and organic molecules toform the matrix.

Ridges fuse and the periosteum becomes theendosteum.

New concentric lamellae are formed.

Osetoblasts under the periosteum form newcircumferential lamellae.


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Bone Growth in Width

Only by appositional growth at the bones surface Periosteal cells differentiate into osteoblasts and form bony ridges

and then a tunnel around periosteal blood vessel.

Concentric lamellae fill in the tunnel to form an osteon.


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Factors That Affect Bone Growth

1. Minerals2. Vitamins3. Hormones4.

Exercise


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Minerals

Calcium Makes bone matrix hardHypocalcemia: low blood calcium levels.

Hypercalcemia: high blood calcium levels.

Phosphorus Makes bone matrix hard

Magnesium Deficiency inhibits osteoblasts

Boron May inhibit calcium loss,

increase levels of estrogens

Manganese Inhibits formation of new bone


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Vitamins

Vitamin A Controls activity, distribution, andcoordination of osteoblasts/osteoclast

Vitamin B12 May inhibit osteoblast activity

Vitamin C Helps maintain bone matrix,deficiency leads to

decreased collagen production whichinhibits bone growth and repair

(scury) disorder due to a lack of Vitamin C

Vitamin D (Calcitriol) Helps build boneby increasing calcium absorption.

Deficiencies result in Rickets in


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Hormones

Human Growth Hormone Promotes general growth of all

body tissue and normal growth in

Insulin-like Growth Factor Stimulates uptake of amino acids

and protein synthesis

Insulin Promotes normal bone growth andThyroid Hormones Promotes normal bone growth and

maturity

Estrogen and Increases osteogenesis at puberty

Testosterone and is responsible for gender

differences of skeletons

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Bone Tissues 1