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
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
CLASSES OF LEVERS CONTINUED
Second Class: Resistance is between the fulcrum and the effort/force- Wheelbarrow
- Rising up on one’s toes
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
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