Bones and Skeletal Tissues - Mission...

1

PowerPoint Lecture Slides prepared by Leslie Hendon University of Alabama, Birmingham

C H A P T E R

Copyright 2011 Pearson Education, Inc.

Part 1

6 Bones and Skeletal Tissues


The Skeletal System consists of bones, cartilages, and joints. Review of Cartilage Location and basic structure

Found throughout adult body Ear and epiglottis Articular cartilages and costal cartilage Larynx, trachea, and nose Intervertebral discs, pubic symphysis, and articular discs

Is surrounded by perichondrium (dense irreg. C.T.)-- functions as a girdle (resists outward pressure) and in growth & repair

Consists primarily of water Resilient tissueit springs back to original shape


Types of Cartilage (review)

All cartilages share some similarities Cell type is the chondrocyte Chondrocytes are located within lacunae Matrix contains Fibers Jellylike ground substance


Gelatinous ground substance

Chondrocyte in a lacuna Elastic fibers

Lacuna

Matrix Chondrocyte in a lacuna

Perichondrium

Chondrocyte in a lacuna

Collagen fibers

(a) Hyaline cartilage (180) (b) Elastic cartilage (470)

(c) Fibrocartilage (285)

Microscopic appearance of cartilage

Figure 6.2


Types of Cartilage (review)

Hyaline cartilage (glassy) Most abundant cartilage Provides support through flexibility & resilience

Elastic cartilagecontains many elastic fibers Able to tolerate repeated bending

Fibrocartilageresists strong compression and strong tension A intermediate between hyaline and dense regular

C.T.


Hyaline cartilages Elastic cartilages Fibrocartilages

Cartilages

Cartilage in external ear Cartilages in nose

Articular cartilage of a joint

Costal cartilage Cartilage in intervertebral disc

Pubic symphysis

Articular cartilage of a joint

Meniscus (padlike cartilage in knee joint)

Cartilage: Where to find different types of cartilage Epiglottis

Larynx

Trachea

Cricoid cartilage

Lung

Respiratory tube cartilages in neck and thorax

Thyroid cartilage

2


Growth of Cartilage

Appositional growth Chondroblasts in surrounding perichondrium

produce new cartilage

Interstitial growth Chondrocytes within cartilage divide and secrete

new matrix Cartilage stops growing when the skeleton stops growing Cartilage regenerates and heals poorly


Bones are the organs of the skeletal system

Bones contain 3 types of tissues Dominated by bone CT Contain nervous tissue and blood CT Contain cartilage in articular cartilages Contain epithelial tissue lining blood vessels


Function of Bones/ Skeletal System

Supportprovides hard framework Movementskeletal muscles use bones as levers Protection of underlying organs Mineral storagereservoir for important minerals

Blood-cell formationbone contains red marrow Energy metabolismosteoblasts secrete osteocalcin:

hormone that stimulates insulin release and release of fat from fat cells


Bone Tissue Bone tissue consists of:

Organic componentscells, fibers, and ground substance

Inorganic componentsmineral salts that invade bony matrix

Unique composition of the extracellular matrix Gives bone exceptional properties 35%organic components

Contributes to flexibility and tensile strength 65%inorganic components

Provide exceptional harness, resists compression


Cell types in Bone

Three types of cells in bone produces or maintain bone Osteogenic cellsstem cells that differentiate into osteoblasts Osteoblastsactively produce and secrete bone matrix

Bone matrix is osteoid Osteocyteskeep bone matrix healthy (maintain the matrix)

One type of cell breaks down or resorbs bone: Osteoclasts Responsible for resorption of bone Are derived from a line of white blood cells Secrete hydrochloric acid (dissolves mineral component of

matrix) and lysosomal enzymes (digests organic component)


A Classification system for Bones

Long boneslonger than wide; a shaft plus ends

Short bonesroughly cube-shaped

Flat bonesthin and flattened, usually curved

Irregular bonesvarious shapes, do not fit into other

categories

3


Classification of Bones

Figure 6.3 Copyright 2011 Pearson Education, Inc.

Gross Anatomy of Bones: two different ways of organizing the matrix/cells and different areas in bones where these types are located

Compact bone dense outer layer of bone

Spongy (cancellous) bone internal network of bone Contains trabeculae: little beams of bone Open spaces between trabeculae are filled with marrow


Structure of a Typical Long Bone

Diaphysisshaft of a bone Epiphysisends of a bone Blood vesselswell vascularized Medullary cavityhollow cavity filled with

yellow marrow Membranes Periosteum, perforating fibers (Sharpeys

fibers), and endosteum


Structure of a Long Bone

Figure 6.4ac

Proximal epiphysis

(b)

(c) (a)

Yellow bone marrow

Endosteum Epiphyseal line

Articular cartilage

Periosteum

Spongy bone

Compact bone Medullary cavity (lined by endosteum)

Compact bone

Compact bone Periosteum Perforating (Sharpeys) fibers Nutrient arteries

Diaphysis

Distal epiphysis

Endosteum


Compact bone

Trabeculae

Spongy bone (diplo)

Figure 6.5

Structure of Short, Irregular, and Flat Bones

Flat bones, short bones, and irregular bones Contain bone

marrow but no marrow cavity

Diplo Internal spongy

bone of flat bones


Load here (body weight)

Head of femur

Compression here

Point of no stress

Tension here

(a)

Gross Anatomy of Bones

Bone design and stress Anatomy of a bone

reflects applied stresses

Compression and tension greatest at external surfaces

Figure 6.6a

4


Figure 6.6b Bone anatomy and bending stress.

Trabeculae of spongy bone

Load here

Compression lines Tension lines


Bone Markings

Superficial surfaces of bones reflect stresses on them

There are three broad categories of bone markings: Projections for muscle attachment Surfaces that form joints Depressions and openings


Bone Markings

Table 6.1 Copyright 2011 Pearson Education, Inc. Table 6.1 (2 of 3)

Copyright 2011 Pearson Education, Inc. Table 6.1 (3 of 3)


Microscopic Structure of Compact Bone Compact Bone

Contains passage ways for blood vessels, lymph vessels, and nerves

Matrix is organized in Osteons (Haversian canals) long cylindrical structures Function in support Structurallyresembles rings of a tree in cross-section Osteons contain:

Lamellae Central canal Perforating canals Canaliculi

5

Copyright 2011 Pearson Education, Inc. Figure 6.7

(a)

Compact bone

Endosteum lining bony canals and covering trabeculae

Perforating (Volkmanns) canal

Perforating (Sharpeys) fibers

Periosteal blood vessel Periosteum

Lamellae

Circumferential lamellae

Osteon (Haversian system)

Central (Haversian) canal

Spongy bone

(c) Interstitial lamellae

Lacunae

Lamellae Central canal

Lacuna (with osteocyte) (b)

Nerve Vein Artery

Canaliculi

Osteocyte in a lacuna

Lacunae

Lamellae Central canal

Microscopic Structure of Compact Bone


Figure 6.7 Microscopic structure of compact bone.

Central (Haversian) canal

Osteon (Haversian system) Circumferential lamellae

Compact bone Spongy bone

Perforating (Volkmanns) canal

Endosteum lining bony canals and covering trabeculae

Lamellae Perforating collagen fiber bundles Periosteal blood vessel Periosteum

Nerve Vein Artery Canaliculi Osteocyte in a lacuna

Lamellae Central canal Lacunae

Osteocyte within lacuna

Central canal

Interstitial lamella


Structures in the central canal

Artery with capillaries

Vein Nerve fiber

Lamellae

Collagen fibers run in different directions

Twisting force

Microscopic structure of a single osteon


Microscopic Structure of Spongy Bone

Spongy Bone Is less complex than compact bone Trabeculae contain layers of lamellae and

osteocytes Are too small to contain osteons


Trabecula

Osteocytes

Endosteum

Marrow space

(b)

(a) Osteoblasts

Microscopic Structure of Compact Bones


Bone Development

Ossification (osteogenesis)bone-tissue formation Membrane bonesformed directly from

mesenchyme, via Intramembranous ossification

Other bonesdevelop initially from hyaline cartilage, via Endochondral ossification

6


Intramembranous Ossification

Figure 6.10, steps 12

Mesenchymal cell Collagen fiber Ossification center Osteoid Osteoblast

Osteoid Osteocyte Newly calcified bone matrix

Osteoblast

Ossification centers appear in the fibrous connective tissue membrane. Selected centrally located mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center.

Bone matrix (osteoid) is secreted within the fibrous membrane and calcifies. Osteoblasts begin to secrete osteoid, which is calcified within a few days.

Trapped osteoblasts become osteocytes.

1 2


Intramembranous Ossification

Figure 6.10, steps 34

Mesenchyme condensing to form the periosteum

Blood vessel

Trabeculae of woven bone

Fibrous periosteum Osteoblast Plate of compact bone Diplo (spongy bone) cavities contain red marrow

Woven bone and periosteum form. Accumulating osteoid is laid down between embryonic blood vessels in a random manner. The result is a network (instead of lamellae) of trabeculae called woven bone.

Vascularized mesenchyme condenses on the external face of the woven bone and becomes the periosteum.

Lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears. Trabeculae just deep to the periosteum thicken and are later replaced with mature lamellar bone, forming compact bone plates.

Spongy bone (diplo), consisting of distinct trabeculae, persists internally, and its vascular tissue becomes red marrow.

3 4


Endochondral Ossification

Forms all bones except some bones of the skull and clavicles

Bones are modeled in hyaline cartilage Begins forming late in the second month of

embryonic development Continues forming until early adulthood


Hyaline cartilage

Area of deteriorating cartilage matrix

Epiphyseal blood vessel

Spongy bone formation

Epiphyseal plate cartilage

Secondary ossification center

Blood vessel of periosteal bud

Medullary cavity

Articular cartilage

Childhood to adolescence Birth Week 9 Month 3

Spongy bone

Bone collar Primary ossification center

Bone collar forms around hyaline cartilage model.

Cartilage in the center of the diaphysis calcifies and then develops cavities.

The periosteal bud invades the internal cavities, and spongy bone begins to form.

The diaphysis elongates and a medullary cavity forms as ossification continues. Secondary ossification centers appear in the epiphyses in preparation for stage 5.

The epiphyses ossify. When completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages.

1 2 3 4 5

Stages in Endochondral Ossification

Figure 6.11



Anatomy of Epiphyseal Growth Areas

In epiphyseal plates of growing bones: Cartilage is organized for quick, efficient growth Cartilage cells form tall stacks

Chondroblasts at the top of stacks divide quickly Pushes the epiphysis away from the diaphysis Lengthens entire long bone

7


Anatomy of Epiphyseal Growth Areas

Older chondrocytes signal surrounding matrix to calcify Older chondrocytes then die and disintegrate

Leaves long trabeculae (spicules) of calcified cartilage on diaphysis side

Trabeculae are partly eroded by osteoclasts Osteoblasts then cover trabeculae with bone tissue Trabeculae finally eaten away from their tips by

osteoclasts


Organization of Cartilage within Epiphyseal Plate of Growing Long Bone

Calcified cartilage spicule

Osseous tissue

Resting zone

Proliferation zone Cartilage cells undergo mitosis.

Hypertrophic zone Older cartilage cells enlarge.

Ossification zone New bone formation is occurring.

Calcification zone Matrix becomes calcified; cartilage cells die; matrix begins deteriorating.

1

2

3

4


Figure 6.12 Organization of the cartilage within the epiphyseal plate of a growing long bone.

Calcified cartilage spicule

Osseous tissue

Cartilage cells undergo mitosis.

Older cartilage cells enlarge.

Matrix becomes calcified; cartilage cells die; matrix begins deteriorating.

New bone is forming.

Resting zone

Proliferation zone

Hypertrophic zone

Calcification zone

Ossification zone

Diagram of the zones within the epiphyseal plate.

Photomicrograph of cartilage in the epiphyseal plate (125).

X-ray image of right knee, anterior view. Proximal epiphyseal plate of the tibia enlarged in part (b).

1

2

3

4


Postnatal Growth of Endochondral Bones

During childhood and adolescence: Bones lengthen entirely by growth of the

epiphyseal plates (endochondral [in the cartilage] growth)

Cartilage is replaced with bone CT as quickly as it grows

Epiphyseal plate maintains constant thickness Whole bone lengthens



As adolescence draws to an end: Chondroblasts divide less often Epiphyseal plates become thinner Cartilage stops growing Replaced by bone tissue

Long bones stop lengthening when diaphysis and epiphysis fuse



Growing bones also widen as they lengthen Osteoblastsadd bone tissue to the external

surface of the diaphysis Osteoclastsremove bone from the internal

surface of the diaphysis This widening is called appositional growth

growth of a bone by addition of bone tissue to its surface

8


Bone Growth influenced by hormones (also nutrition)

Growth hormoneproduced by the pituitary gland Stimulates epiphyseal plates

Thyroid hormoneensures that the skeleton retains proper proportions

Sex hormones (estrogen and testosterone) Promote bone growth Later induces closure of epiphyseal plates


Bone Remodeling

Bone is dynamic living tissue 500 mg of calcium may enter or leave the

adult skeleton each day Bone matrix and osteocytes are continually

removed and replaced Cancellous bone of the skeleton is replaced

every 34 years Compact bone is replaced every 10 years


Bone Remodeling

Bone deposit and removal Occurs at periosteal and endosteal surfaces

Bone remodeling Bone depositionaccomplished by

osteoblasts Bone reabsorptionaccomplished by

osteoclasts


Remodeling, Spongy Bone

Figure 6.13

Compact bone

Spongy bone

Trabeculae of spongy bone

Resorption of bone matrix by osteoclasts

Deposition of new bone by osteoblasts

New bone

Osteoblast Osteoblast Osteoclast


OsteoclastA Bone-Degrading Cell

A giant cell with many nuclei Crawls along bone surfaces Breaks down bone tissue Secretes

concentrated HCl Lysosomal

enzymes are released

Derived from hematopoietic stem cells

Figure 6.14

Osteocyte within a lacuna

Bone matrix

Ruffled border of osteoclast Nuclei


Repair of Bone Fractures

Simple and compound fractures Treatment by reduction-- realignment of the

broken ends of the bone Closed reduction-- manually Open reduction-- surgically with pins or wires

9


Stages of Healing a Fracture

Figure 6.15

Hematoma External callus

New blood vessels

Spongy bone trabecula

Internal callus (fibrous tissue and cartilage)

A hematoma forms. Fibrocartilaginous callus forms.

Bony callus forms.

Bony callus of spongy bone Healed fracture

Bone remodeling occurs.

1 2 3 4


Common Types of Fractures

Table 6.2 (1 of 3)



Table 6.2 (2 of 3) Copyright 2011 Pearson Education, Inc.


Table 6.2 (3 of 3)


Disorders of Bones

Osteoporosis Characterized by low bone mass Bone reabsorption outpaces bone

deposition Occurs most often in women after

menopause


Osteoporosis

Figure 6.16

10


Disorders of Bones

Osteomalacia Occurs in adultsbones are inadequately

mineralized (not enough vitamin D or calcium phosphate in diet)

Rickets Occurs in childrenanalogous to

osteomalacia & same cause


Figure 6.17 Rickets.


Disorders of Bones

Pagets disease Characterized by excessive rate of bone

deposition & resorption--- results in immature matrix

Osteosarcoma A form of bone cancer


The Skeleton Throughout Life

Cartilage grows quickly in youth Skeleton shows fewer chondrocytes in the

elderly Bones are a timetable Mesoderm Gives rise to embryonic mesenchyme cells

Mesenchyme Produces membranes and cartilage

Membranes and cartilage ossify


The Skeleton Throughout Life

Skeleton grows until the age of 1821 years In children and adolescents, bone formation

exceeds rate of bone reabsorption In young adults, bone formation and bone

reabsorption are in balance In old age, reabsorption predominates Bone mass declines with age


Figure 6.18 Primary ossification centers in the skeleton of a 12-week-old fetus.

Frontal bone of skull

Mandible

Radius Ulna Humerus

Femur

Tibia

Ilium Vertebra

Ribs

Scapula Clavicle

Occipital bone

Parietal bone

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