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SKELETAL TISSUESCHAPTER 7

By John McGillSupplement Outlines: Beth WyattOriginal PowerPoint: Jack Bagwell

INTRODUCTION TO THE SKELETAL SYSTEM

• STRUCTURE– Organs: Bones– Related Tissues: Cartilage and Ligaments

• PRIMARY FUNCTION– Support

• PRIMARY TISSUES OF THE SKELETAL SYSTEM– BONE TISSUE– CARTILAGE

• Connective Tissues

TYPES OF BONES

• LONG: Long and Narrow• Humerus and femur• SHORT: Cube/Box-

Shaped– carpus and tarsus– found in parts of skeleton

that require strength and limited movement

• FLAT: Flat and Thin• IRREGULAR: Complex

Shapes

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MACROSCOPIC STRUCTURE:

Long Bones• DIAPHYSIS

– Shaft– Composed of Compact

Bone• EPIPHYSES

– Both Ends Composed of Cancellous Bone

• ARTICULAR CARTILAGE– “Joining Cartilage”– Covers Epiphyses (Thin

Layer)– Provides Cushioning at

Joints

MACROSCOPIC STRUCTURE:

Long Bones• PERIOSTEUM

– Bone’s Covering– White– Thin but Tough– “Welded” to Underlying Bone– Contains Blood Vessels

• MEDULLARY (MARROW) CAVITY– Space Within the Diaphysis– Contains Bone Marrow

• ENDOSTEUM– Lines the Medullary Cavity– Thin

MACROSCOPIC STRUCTURE:SHORT, FLAT, IRREGULAR BONES

• Inner Portion: Cancellous Bone– “spongy bone”

• Surfaces: Compact Bone– dense and solid

• Periosteum Present

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MICROSCOPIC STRUCTURE OF BONE: COMPACT BONE:

• HAVERSIAN SYSTEMS (OSTEONS)– Microscopically,

Compact Bone is Composed of Haversian Systems

– Haversian Systems: Microscopic Structural Units of Compact Bone

Microscopic structure - Haversian System

• Haversian system (osteon)-consists of the canal and surrounding structures

• Lamellae – concentric layers of calcified matrix

• Lacunae – “little lakes”; where the bone cells live

• Canaliculi – very small canals that radiate from the lacunae; carry nutrients

• Haversian canal – central canal which carries blood vessels

• FUNCTION OF HAVERSIAN SYSTEMS– Blood Supply to Compact Bone– Periosteum Haversian Canals

Canalculi Lacunae

BONE (MICROSCOPIC VIEW)

canaliculi osteocyte in lacunae

Haversian canal

ossified matrix (lamellae)

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CANCELLOUS BONE: TRABECULAE

• Trabeculae: Needlelike Pieces of Bone (Surround Spaces)

• Contains Osteocytes• How Cancellous Bone Gets Its Blood Supply: • From Bone Marrow by Diffusion (Periosteum

Bone Marrow Openings in Trabeculae)

BONE TISSUE (OSSEOUS TISSUE)• COMPONENTS: MATRIX, PROTEIN FIBERS, CELLS

– Typical Connective Tissue• COMPOSITION OF BONE MATRIX

– INORGANIC COMPONENTS• Minerals (Esp. Ca and Phosphate)• Forms hydroxyapatite• Constitute Approx. 65% of Bone Matrix• Gives Matrix Hardness and Strength

– ORGANIC COMPONENTS• Complex Mixture of Carbohydrates and Proteins• Gives Matrix Strength

• PROTEIN FIBERS: COLLAGENOUS– Also Gives Matrix Strength

• *NOTE: Matrix with Protein Fibers Means Hardness and Strength

BONE CELLS• OSTEOBLASTS

– Bone-Forming Cells– Location: Periosteum (Primarily)

• OSTEOCLASTS– Bone-Destroying Cells– Location: Endosteum (Primarily)

• OSTEOCYTES– Bone Cells (Mature Osteoblasts)– Locations:

• 1) Compact Bone: Lacunae• 2) Cancellous Bone: Trabeculae

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BONE MARROW (MYELOID TISSUE)• Tissue Type:

Connective Tissue (Reticular)

• LOCATIONS– Long Bones:

• Medullary Cavity• Epiphyses:

– Spaces in Cancellous Bone

– Short, Flat, Irregular Bones:

• Spaces in CancellousBone

BONE MARROW TYPES: RED MARROW

• DESCRIPTION/FUNCTIONS– Red in Color Because

Functions in Hematopoiesis• LOCATIONS

– Children: All Bones Contain Red Marrow

– Adults: Certain Bones Contain Red Marrow

• Flat Bones of the Skull• Sternum, Ribs, Vertebrae• Pelvic Bones• Epiphyses of Humerus and Femur

BONE MARROW TYPES: YELLOW MARROW

• DESCRIPTION/FUNCTIONS– Yellow in Color Because

Contains Largely Adipose Tissue

– Yellow Marrow Was Once Red Marrow, Now Yellow B/C

– It No Longer Functions in Hematopoiesis

• LOCATIONS– Most Bones in Adults Contain

Yellow Marrow

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Functions of Bones• Support – support the weight of the rest of

the body• Protection – protect the delicate body parts• Movement – muscles attach to bone and

allow movement• Mineral storage – calcium, phosphorous,

and other minerals are stored in the bone• Hematopoiesis – red marrow plays an

important role in the formation of red blood cells, some flat bones also play a role here

DEVELOPMENT OF BONE

(OSTEOGENESIS)• How Bones Form in the Fetus• INTRAMEMBRANOUS OSSIFICATION

– DEFINITION• “Within Membrane Bone

Formation”• Method by Which Flat Bones

Form• MECHANISM

– Connective Tissue Membrane – Cells Develop Into Osteoblasts– Secrete Organic Matrix and

Collagenous Fibers– Calcification Occurs

•Intramembranous bone formation in a fetal pig skull. •Flat bones of the skull develop by IO. •Embryonic mesenchyme cells form a membrane (Mes) & •differentiate into osteoblasts that•form bony spicules or cancellousbone (CsB). •Eventually osteonsform.

DEVELOPMENT OF BONE (OSTEOGENESIS)• ENDOCHONDRAL OSSIFICATION

– DEFINITION• “Within Cartilage Bone

Formation”• Method by Which Most Bones

Form– MECHANISM

• Cartilage Model • Periosteum Forms • Cells Develop Into

Osteoblasts• Secrete Organic Matrix and

Collagenous Fibers• Calcification Occurs

– *Note: In Both Types of Ossification:

• Osteoclasts Resorb Bone • Forms Medullary Cavity,

Spaces in Cancellous Bone

ENDOCHONDRAL OSSIFICATION

• Embryonal hyaline cartilage precedes bone formation.

• Inner cells change into osteoblasts cells in the perichondrium.

• Osteoblasts form the periosteum.

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Summary: Endochondral Ossification

• Bone forms from a cartilage model• Osteoblasts begin to calcify the cartilage• Osteoblasts and osteoclasts are constantly

reshaping the bone• Centers of ossification appear in the

epiphyses• Epiphyseal plate is site of continued bone

growth; indicates the bone is not yet mature.

Osteogenesis (Bone formation)• The cartilaginous skeleton is changed to bone in one

of two ways:• Intramembranous ossification – happens in some flat

bones of body– 1st step – cells differentiate into osteoblasts (centers of

ossification)– 2nd – cells secrete ground substance– 3rd – ground substance is calcified– 4th – trabelculae appear and join to form spongy bone– 5th - layer of spongy bone is covered on both sides by

compact bone– 6th – growth occurs by appositional growth – the addition of

osseous tissue to its outer surface

Bone Growth - Animation

•http://www.anatomy.gla.ac.uk/fab/tutorial/generic/bonet.html

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FETAL SKELETON

BONE GROWTH AND RESORPTION• How Bones Increase in Size after Birth• Involves Bone Resorption : Destruction• BONE GROWTH

– FLAT BONES (Also Short, Irregular Bones)• APPOSITIONAL GROWTH

– Growth By Adding to the Surfaces

– LONG BONES• GROWTH IN LENGTH – EPIPHYSEAL PLATE• Epiphyseal Plate: Layer of Hyaline Cartilage That Lies B/T Epiphyses

and Diaphysis• Didn’t Ossify During the Fetal Period (Purpose: To Allow Bone

Growth in Length)• Epiphyseal Plate 1) Thickens and 2) Ossifies Repeatedly• When Growth in Length is Complete, Cells in EP Stop Mitosis and

the Entire Plate Ossifies, What Remains is Epiphyseal Line

EPIPHYSEAL PLATE

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Epiphyseal Plate• The epiphyseal plate

allows for growth in bones.

Zones of the Epiphyseal Plate

GROWTH IN DIAMETER – COMBINED ACTION OF OSTEOBLASTS AND OSTEOCLASTS

• Osteoblasts(Periosteum) Build New Bone on the Outer Surface

• Osteoclasts(Endosteum) Destroy Bone from the Inner Surface of the Medullary Cavity (Enlarges Med. Cavity)

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BONE GROWTH AND RESORPTION

• BONE RESORPTION– Osteoclasts (Endosteum) Destroy Bone

from the Inner Surface of the MedullaryCavity

BONE GROWTH AND RESORPTION• BONE GROWTH AND RESORPTION

THROUGHOUT LIFE– Both Growth and Resorption Go On

Throughout Life, But at Different Rates• From Infancy Young Adulthood: Growth

EXCEEDS Resorption (Bones Grow and are Thick)

• During Late 20’s/Early 30’s: Growth EQUALS Resorption (Bones Remain Relatively Constant)

• From Mid 30’s/Early 40’s Old Age: Resorption EXCEEDS Growth (Bones Become Thinner, More Susceptible to Fracture and Disease)

BONE GROWTH AND RESORPTION

• BONES RESPONSE TO STRESS– Bone Stress = Weight Bearing Applied

to Bones– Bone Stress Increases the Activity of the

Osteoblasts (Helps Offset the Effects of Aging on Bones)

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REPAIR OF BONE

FRACTURES

• FRACTURE: A Break in the Continuity of Bone

FRACTURE HEALING

• VASCULAR DAMAGE– Damage to Blood

Vessels

FRACTURE HEALING

• FORMATION OF FRACTURE HEMATOMA– Blood Clot Forms in

the Area of the Fracture in Order to Stop Bleeding

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FRACTURE HEALING

• FORMATION OF CALLUS TISSUE– Thickened Repair

Tissue That Binds the Ends of the Bones Together (Reason That the Fracture is Aligned and Immobilized)

FRACTURE HEALING

• REPLACEMENT BY BONE– Callus Tissue

Becomes Bone (Action of Osteoblasts), Remodeled by Osteoclasts

Epiphyseal Plate Fracture

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CARTILAGE• CHARACTERISTICS

– MATRIX• FIRM/FLEXIBLE GEL

– PROTEIN FIBERS• COLLAGENOUS

– CELLS• CHONDROCYTES• Chondrocytes Lie in

Lacunae– AVASCULAR: Oxygen

and Nutrients by Diffusion

CARTILAGE: Types

• Hyaline• Elastic• Fibrocartilage

HYALINE CARTILAGE• Most Abundant and

Common• Shiny• Semitransparent• Locations:

– Articular Cartilage– Costal Cartilages– Cartilage Rings in

Trachea and Bronchi– Tip of Nose

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ELASTIC CARTILAGE• Has Fewer Collagenous

Fibers Compared to Hyaline

• In Addition, Contains Elastic Fibers

• Locations: – External Ear– Epiglottis– Eustachian Tube

FIBROCARTILAGE

• Cartilage With the Most CollagenousFibers

• Locations: – Symphysis Pubis– Intervertebral Disks– Menisci in Knee

GROWTH OF CARTILAGE• INTERSTITIAL (ENDOGENOUS)

GROWTH– DEFINITION: “Growth From Within”– OCCURS WHEN: During Childhood and

Adolescence• APPOSITIONAL (EXOGENOUS)

GROWTH– DEFINITION: “Growth by Adding to the

Surfaces”– OCCURS WHEN: During Adulthood