FUNCTION(S) OF THE
SKELETAL SYSTEM
•
•
•
•
•
Support
Protection
Movement
Mineral storage
Formation of blood cells
Hematopoiesis
CLASSIFICATION OF
BONES
• Types of Osseous Tissue
– Compact (dense) Bone
– Spongy (cancellous) Bone
spongy bone
compact bone
TYPES OF OSSEOUS TISSUE
Long Bones
A shaft with two widened ends
Compact and spongy bone
 Examples:
Humerus
 Radius & ulna
 Femur
 Tibia & fibula
 Phalanges

Femur
TYPES OF OSSEOUS TISSUE
Short Bones
Cube-shaped bones
Mostly spongy bone
 Examples:

Wrist and ankle bones
Tarsal
Sesamoid bones
 Short bones embedded with a tendon

Example: Patella
Patella
TYPES OF OSSEUS TISSUE
Flat Bones
Thin, flat bones
Layer of spongy bone between
layers of compact bone
Examples:
 Sternum
 Ribs
 Skull
Parietal
TYPES OF OSSEOUS TISSUE
Irregular Bones
Irregular shape
Mostly spongy bone
 Examples:

Vertebrae

Hip bones
Vertebra
BONE STRUCTURE
Diaphysis
Shaft of bone
Compact bone surrounds
medullary cavity
 Contains yellow marrow (fat)
medullary cavity
BONE STRUCTURE
Epiphyses
proximal
epiphysis
Widened end of long bones
Spongy bone
May contain red marrow
Epipheseal line or plate
 Bone growth during childhood
 Actively mitotic plate of hyaline cartilage
Articular cartilage covers joint surface
distal epiphysis
BONE STRUCTURE
Bone Membranes
Periosteum
 Outer C.T. membrane
 Inner surface may contain
osteoblasts or osteoclasts
 Blood vessels and nerves
periosteum
BONE STRUCTURE
Bone Membranes
Endosteum
 Inner C.T. membrane
 Lines marrow cavities, Haversian canals
and covers trabeculae
 Contains osteoblasts and osteoclasts
endosteum
BONE MARROW
Red Bone Marrow
Spongy bone
Found in spongy bone
Hematopoietic tissue
Found in:
 Head of femur and humerus
 Sternum and hip bones in adults
spaces containing red bone
marrow
BONE MARROW
yellow bone marrow
Yellow Bone Marrow
Composed of fat
Found in:
 Medullary cavity
May convert to red marrow
BONE HISTOLOGY: Compact
Bone
Haversian canals
concentric lamella
Volkmann’s canal
lacuna
canaliculi
BONE HISTOLOGY: Compact
Bone
Haversian Systems (Osteons)
Lamellae
 Concentric, interstitial & circumferential
Haversian canals
Volkmann's canals
Osteocytes within lacunae
Canaliculi
BONE HISTOLOGY: Osteon
Haversian canal
Volkmann’s canal
BONE HISTOLOGY: Spongy
Bone
Spongy Bone
No osteons
Scattered trabeculae for support
Called diploe in flat bones
Red marrow between trabeculae
diploe
CHEMICAL COMPOSITION OF
BONE
Organic Components
1/3 of matrix
Includes all 3 cell types
Osteoblasts secrete osteoid = Organic bone matrix
Inorganic Components
2/3 of matrix
Accounts for bone hardness
Hydroxyapatites [Ca10(PO4)6(OH)2]
 Mineral salts of calcium phosphate
BONE MARKINGS
Structures on the external surface of bone
Caused by:
Muscle or ligament attachments
Blood vessels, nerves etc. travel
Be familiar with the types of markings found on bones (see Table
6.1 in your textbook or the list in your lab notebook)
OSTEOGENESIS/OSSIFICATION
Osteogenesis
Process of bone formation
Used for:
 Formation of bony skeleton in embryos
 Bone growth during childhood and early adulthood
 Bone remodeling and repair in adults
OSTEOGENESIS/OSSIFICATION
Two Types of Bone Formation
Intramembranous Ossification
 Bone develops from a fibrous membrane
Endochondral Ossification
 Bone develops from a hyaline cartilage model
Intramembranous Ossification
INTRAMEMBRANOUS
OSSIFICATION
 Used for formation of flat bones (skull & clavicles)
Steps

Formation of bone matrix within fibrous membrane





Initial ossification sight ( 8 wks)  A fibrous C.T. membrane
Ossification center appears in the C.T. membrane
Osteoid secreted by osteoblasts
Osteoid becomes mineralized
Formation of woven bone
 Network of bony trabeculae forms = woven bone

Formation of compact bone plates
 Trabeculae thicken at the edge, forming compact bone
 Spongy bone remains in the center
ENDOCHONDRAL
OSSIFICATION
hyaline cartilage
perichondrium
periosteum
deteriorating cartilage
matrix
ENDOCHONDRAL
OSSIFICATION
 Used for formation of most bones of the skeleton (2nd month)
Steps

Formation of bone collar around hyaline cartilage model
 Perichondrium around hyaline cartilage model converted to periosteum
 Osteoblasts secrete osteoid onto the external shaft of the “hyaline” bone

Deterioration of cartilage matrix
 Matrix within the hyaline shaft deteriorates
ENDOCHONDRAL
OSSIFICATION
secondary ossification center
articular cartilage
blood vessel periosteal
bud
medullary cavity
epiphyseal plate
open spaces forming
bone
ENDOCHONDRAL OSSIFICATION
Steps

Formation of spongy bone by periosteal bud
 Periosteal bud invades the internal cavity
 Contains blood vessels and osteoblasts
 Osteoblasts produce trabeculae of bone

Formation of medullary cavity
 Osteoclasts break down new bone forming a medullary cavity

Ossification of epiphyses
 Secondary ossification centers form in epiphyses shortly before or after birth
 Spongy bone forms
 Hyaline cartilage remains only at the epiphyseal plate and articular surfaces
BONE GROWTH IN LONG
BONES
Growth in Length
•Cartilage growth in epiphyseal plate
•Cartilage replaced by bone
•Bone remodeled
•Bone resorption
Growing Bone
Adult Bone
BONE GROWTH IN LONG
BONES
Long bones lengthen by growth of the epiphyseal plates
Harden at the end of puberty
All bones grow in width or change shape by appositional
growth
BONE GROWTH IN LONG
BONES
Growth in the Epiphyseal Plate
Hyaline plate contains dividing chondrocytes
Chondrocytes enlarge
 Pushed towards diaphysis
 Eventually die
Osteoblasts secrete bone matrix
 Form small bone spicules
BONE GROWTH IN LONG
BONES
Growth in the Epiphyseal Plate (cont.)
Epiphyseal plate activity stimulated by growth hormone during
childhood
Sex hormones (testosterone & estrogen)
 Adolescent growth spurt
End of adolescence
 Epiphyseal plate replaced by bone
 Longitudinal bone growth ends
BONE GROWTH IN LONG
BONES
Appositional Growth
Used to widen bones for remodeling
Osteoblasts on the periosteum:
 Form new Haversian systems on outer bone surface
 Increase thickness of compact bone
Osteoclasts on the endosteum
 Resorb bone
 Enlarge medullary cavity
BONE GROWTH IN LONG
BONES
Appositional Growth
•Bone addition
•Bone resorption
Growing Bone
Adult Bone
BONE REMODELING & REPAIR
 Bone Remodeling
Bone deposited and resorbed daily at the periosteal and endosteal surfaces
5 to 7% of bone mass recycled weekly
Rate of resorption should = rate of deposit
Response to blood calcium levels
Ca2+ ions are needed for nerve impulse transmission, muscle contractions, blood
coagulation
 Vitamin D enhances absorption of Ca2+ from the intestine

When remodeling occurs is determined by mechanical and gravitational forces
Heavier bone usage  heavier bones
Nonuse  bone wasting
BONE REMODELING &
REPAIR
Bone Deposit
Osteoblasts deposit osteoid which is later mineralized into hard
bone
 Hormonal Control

Calcitonin
Produced by “C” cells in the thyroid glands
 Secreted when blood Ca2+ levels 
 Inhibits bone resorption, enhances Ca2+ deposit in bone matrix

BONE REMODELING &
REPAIR
Bone Resorption
Osteoclasts secrete enzymes
 Digest organic matrix
Osteoclasts secrete acids
 Make calcium salts more soluble
Minerals freed from bone are put into bloodstream
 Hormonal Control

Parathyroid Hormone (PTH)
Produced by the parathyroid glands
 Secreted in response to low blood Ca2+ levels
 Stimulates bone resorption

CALCIUM HOMEOSTASIS: PTH
CONTROL
BONE
PTH promotes Ca2+ release into the
blood
Ca2+ removed from blood by
osteoblasts
BLOOD
PTH promotes Ca2+ reabsorption from
urine
Ingested Ca2+
KIDNEY
Unabsorbed Ca2+ lost in feces
SMALL INTESTINE
Ca2+ lost in the urine
PTH promotes Vitamin D
formation
Vitamin D promotes Ca2+ absorption
FRACTURES
Fracture
Break in the bone
Fracture Types
Simple
Compound
Comminuted
Compression
Depression
Impacted
Spiral
Greenstick
TYPES OF FRACTURES
greenstick fracture
fissured fracture
transverse fracture
oblique fracture
comminuted fracture
spiral fracture
FRACTURE REPAIR
Phases of Repair
Hematoma Formation
 Blood clot forms
hematoma
FRACTURE REPAIR
Phases of Repair
Fibrocartilaginous Callus
Formation
 Fibroblasts secrete collagen
fibrocartilage
 Condroblasts secrete cartilage
matrix
 Osteoblasts form spongy bone
spongy bone
FRACTURE REPAIR
Phases of Repair
Bony Callus Formation
 Osteoclasts and osteoblasts convert callus
into a bony callus
bony callus
FRACTURE REPAIR
Phases of Repair
Bony Callus Remodeling
 Continues for several months
compact bone
BONE IMBALANCES
Osteoporosis
A group of diseases in which bone resorption exceeds bone
deposit = reduction in bone mass
 Vertebrae and neck of femur most susceptible
 Most common in postmenapausal
reduction
women due to estrogen
BONE IMBALANCES
Osteoporosis
Risk Factors
 Insufficient exercise
 Poor calcium or protein intake in diet
 Vitamin D or calcitonin metabolism problems
 Smoking
 Drinking
 Immobility
BONE IMBALANCES
Osteomalacia
Disorders in which bone is inadequately mineralized
Osteoid is deposited but calcium salts are not
Weight-bearing bones fracture, bend or deform
 Rickets may occur in children with insufficient calcium or Vitamin D
intake

Causes bowed legs and deformities of the pelvis
BONE IMBALANCES
Paget’s Disease
Characterized by excessive, abnormal bone formation and
resorption
Bone produced contains a high ratio of woven bone to compact
bone
Bone mineralization is reduced
Bones become soft and weak