SKELETAL SYSTEM

SKELETAL SYSTEM FUNCTIONS

Support (Primary function)Movement (Passive)Protection of Vital OrgansMineral StorageBlood Cell Formation (Hematopoiesis or

Hemopoiesis)

OSSEOUS TISSUE

Cancellous (spongy) BoneCompact (dense) BoneBone Cells

- Osteoblasts – Secrete to form bone- Osteocytes

* Mature bone cells* “Trapped” osteoblasts

- Osteoclasts – destroy bone* Enzymes digest protein* Acids dissolve minerals* Forms Marrow Cavity; Involved in Remodelling

CANCELLOUS OR SPONGY BONE

- Open spaces, light weight

- Lattice arrangement

- Made of microscopic trabeculae subunits

- Location of bone marrow

- Site of blood cell formation (red marrow)

- Within epiphyses of long bones

COMPACT OR DENSE BONE

- Dense, Ivory-like

- Forms the outside layer of bones

- Forms Diaphyses of long bones

- Made of microscopic osteon (Haversian system) subunits

Axial skeletonAxial skeleton

Appendicular skeletonAppendicular skeleton

STRUCTURAL CLASSIFICATION:

APPENDICULAR AND AXIAL

STRUCTURAL CLASSIFICATION BASED ON BONE SHAPE

TYPE OF BONE EXAMPLE

Long bones Femur

Flat bones Frontal bone

Short bones Carpals

Irregular bones Vertebrae

Long BoneIrregular Bone

Flat Bone

Short Bones

STRUCTURAL CLASSIFICATION BASED ON TYPE OF BONE

ANATOMY OF A LONG BONE

Periosteum Epiphysis Diaphysis Compact bone Spongy bone Medullary cavity Endosteum Nutrient foramen Epiphyseal line

Epiphysis

Diaphysis

Spongy bone

Compact bone

Medullary cavity

Epiphyseal line

BONE DEVELOPMENT

Ossification = replacement of other tissues with bone

Begins about the 6th week of gestationSize increases until late teens (females) to mid-

twenties (males)Requires Ca2+

Ossification processes include:

- Intramembranous bone formation

- Endochondral bone formation

GENERAL FEATURES OF INTRA-MEMBRANOUS BONE FORMATION

* Occurs in flat bones of skull, clavicles

* Begins with collagenous fiber membrane model

* Membrane calcifies into compact bone

* Fontanels (“Soft spot”, not yet ossified)

THE PROCESS OF INTRA-MEMBRANOUS BONE FORMATION

* C.T. Cells cluster & centers of ossification appear

* Cells differentiate into osteoblasts* Osteoblasts secrete a matrix, forming

trabeculae* Calcium salts are deposited

* Trabeculae fuse into spongy bone lattice

* Lattice fills with red bone marrow

* Eventually, peripheral trabeculae thicken into compact bone (periosteal ossification)

THE PROCESS OF INTRA-MEMBRANOUS BONE FORMATION

CONTINUED

* Occurs in remainder of skeleton

* Begins with hyaline cartilage model

* Cartilage is replaced by bony tissue

GENERAL FEATURES OF ENDOCHONDRAL BONE FORMATION

THE PROCESS OF ENDOCHONDRAL BONE FORMATION

FORMATION OF BONE COLLAR

- Cartilage model is covered by perichondrium

- Perichondrium becomes periosteum

- A “collar” of bone is produced around the diaphysis

THE PROCESS OF ENDOCHONDRAL BONE FORMATION

CALCIFICATION OF DIAPHYSEAL CARTILAGE- Hypertrophy of chondrocytes

- Surrounding matrix calcifies

- Diffusion disabled, chondrocytes die

- Cartilaginous matrix disintegrates

THE PROCESS OF ENDOCHONDRAL BONE FORMATION CONTINUED

FORMATION OF PRIMARY OSSIFICATION CENTER- Diaphysis penetrated by blood vessels,

osteoblasts, osteoclasts- Marrow cavity formed by osteoclasts- Trabeculae form (Spongy bone) - Cartilage model grows at ends,

elongating bone

THE PROCESS OF ENDOCHONDRAL BONE FORMATION CONTINUED

FORMATION OF SECONDARY CENTER OF OSSIFICATION- Blood vessels reach epiphyses- Secondary ossification centers develop- Spongy bone is formed- Cartilage is replaced by bone, except at

articular surfaces- Cartilage remains at epiphyseal plate

(metaphysis) until growth is complete

FRACTURES AND THEIR REPAIR

Definition: Any break in a boneRepair may take monthsTypes include

- Simple (skin not broken)

- Compound (bone protrudes through skin)

- Greenstick (shaft bent/broken)

- Spiral (twisting force, ragged break)

- Comminuted (shattered into fragments)

STEPS IN FRACTURE REPAIR

- Broken blood vessels form a fracture hematoma

- C.T. and Capillaries invade site, form fibrocartilage callus

- Repair cells (osteoblasts) are activated in about 48 hours

- Bony callus replaces fibrocartilage callus- Bony callus is remodeled by osteoclasts

BONES AS LEVERS

Lever: A rigid rod that moves about a fixed point

Fulcrum: The fixed point around which a lever moves (joints)

Forces: Act to move levers at two points- Resistance: Force to be overcome- Effort or Work: Force required to overcome

resistance; supplied by skeletal muscles

CLASSES OF LEVERS

First Class: The fulcrum is between the effort/force and the resistance- Seesaw

- Tilting head backward

FIRST CLASS LEVER

F

R

E

R

E

R

E

R

E

R

E

R

E

R

E

CLASSES OF LEVERS CONTINUED

Second Class: Resistance is between the fulcrum and the effort/force- Wheelbarrow

- Rising up on one’s toes

SECOND CLASS LEVER

F

R

ER

E

R

E

R

E

R

E

R

E

R

E

R

E

Third Class: The effort/force is between the fulcrum and the resistance- Most common type in the human body

- Flexing the elbow

CLASSES OF LEVERS CONTINUED

THIRD CLASS LEVER

F

R

ER

ERERER EER

R ER

E

ARTICULATIONS: CLASSIFICATION BY

FUNCTIONCLASSIFICATION FUNCTION

Synarthrosis Immovablejoints

Amphiarthrosis Slightly movablejoints

Diarthrosis Freely movablejoints

ARTICULATIONS: CLASSIFICATION BY

STRUCTURECLASSIFICATION STRUCTURE

Fibrous joint Sutures of skull

Cartilagenous joint Pubic symphysis

Synovial joint Knee

ARTICULATIONS: EXAMPLES

SuturesFunctional: SynarthrosisStructural: Fibrous

KneeFunctional: DiarthrosisStructural: Synovial

Pubic symphysisFunctional: AmphiarthrosisStructural: Cartilagenous

STRUCTURE OF A SYNOVIAL JOINT

Articular cartilage – cover bone endsSynovial membrane – lines joint capsuleSynovial fluid – lubricates & nourishes

cartilageSynovial cavityJoint capsule – fibrous C.T.Ligaments – reinforce jointBursae – synovial sacs at other sites of

friction

TYPES OF SYNOVIAL JOINTS

Classified based on shape of articular surfaces

Gliding (plane)HingePivotEllipsoidal (condyloid)SaddleBall-and-socket