What is?

Hematopoiesis

Bone Formation• Fetal

– INTRAMEMBRANOUS OSSIFICATION– ENDOCHONDRAL OSSIFICATION

• From birth to young adult– APPOSITIONAL (flat, short, irregular

bones)• Increase diameter for ALL bones

– INTERSTITIAL (EPIPHYSEAL PLATE)• Increase length

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

• These are both Connective Tissues

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

• “spongy bone”

Inner Portion: Cancellous Bone

• dense and solid

Surfaces: Compact Bone

Periosteum Present

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 SystemHaversian 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)

CANCELLOUS BONE: TRABECULAE

• Trabeculae: Needlelike Pieces of Bone (Surround Spaces)

• Contains Osteocytes• How Cancellous Bone Gets Its Blood Supply:

– Periosteum Bone Marrow Openings in Trabeculae

BONE TISSUE isOSSEOUS TISSUE

COMPONENTS: MATRIX, PROTEIN FIBERS, CELLS• Typical Connective Tissue

COMPOSITION OF BONE MATRIX• INORGANIC COMPONENTS

• Minerals (Esp. Ca and Phosphate)• Forms hydroxyapatite

• Gives Matrix Hardness and Strength• ORGANIC COMPONENTS

• Complex Mixture of Carbohydrates and Proteins• Gives Matrix Strength

• PROTEIN FIBERS: COLLAGENOUS

Types of 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

BONE MARROW is MYELOID TISSUETissue Type: Connective Tissue• Reticular

LOCATIONS

• Long Bones: • Medullary Cavity• Epiphyses: • Spaces in Cancellous

Bone• Short, Flat, Irregular Bones: • Spaces in Cancellous Bone

Myeloid tissue is a biologic tissue with the ability to perform hematopoiesis.

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

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

Fetal Bone FormationOsteogenesis

• The cartilaginous skeleton is changed to bone in one of two ways:– Intramembranous ossification– Endochondral ossification

#1. INTRAMEMBRANOUS

OSSIFICATION

• How Bones Form in the Fetus– 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 cancellous

bone (CsB). • Eventually osteonsform.

#2. ENDOCHONDRAL OSSIFICATION• 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

• Embryonal hyaline cartilage is model for bone formation.

• Osteoblasts begin to calcify the cartilage

• Osteoblasts and osteoclasts are constantly reshaping the bone

• Epiphyseal plate is site of continued bone growth; indicates the bone is not yet mature.

Bone Growth - Animation

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

FETAL SKELETON

BONE GROWTH AND RESORPTION• How Bones Increase in Size after Birth

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

– Growth By Adding to the Surfaces– LONG BONES grow in length by 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

Epiphyseal PlateThe epiphyseal plate allows for growth in bones.

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)

• http://www.youtube.com/watch?v=6Cn4uusbGk8

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)

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

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

CARTILAGE• CHARACTERISTICS

– MATRIX• FIRM/FLEXIBLE GEL

– PROTEIN FIBERS• COLLAGENOUS

– CELLS• CHONDROCYTES• Chondrocytes Lie in

Lacunae– AVASCULAR: Oxygen

and Nutrients by Diffusion

Similarities and Differences

Bone Cartilage

f l

Similarities and Differences

Bone Cartilage

ChondrocytesJoints,avascul

arGel matrix

CollagenGround substance/matrixCellsProtectionConnective tissueMitosis (both grow)Appositional, insterstitialLacunae

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

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 Collagenous Fibers

• 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