What are the 5 functions of the skeleton?
- Support
- Protection
- Movement
- Mineral storage —> calcium phosphate
- Produces blood cells —> 1 trillion/day
What are the 2 sections of the skeleton?
- Axial —> inner
- cranium, vertebral column, rib cage - Appendicular —> outer
- pectoral girdle, pelvic girdle, upper
limbs, lower limbs
What are the 2 components of bones?
- Cells
- Matrix (osteoid)
What are the 4 components of bone matrix?
Organic (40%):
1. Type 1 collagen - 90%
2. Ground substance - 10%
—> proteoglycans
—> glycoproteins
—> cytokines
—> growth factors
Inorganic (60%):
3. Calcium hydroxyapatite
4. Osteocalcium phosphate
What are the 4 types of bone cells?
- Osteogenic = ‘stem’
- in marrow + deep periosteum - Osteocyte = mature
—> senses mechanical strain —> directs
osteoblast/clast activity
- osteoblast embedded in osteoid
secretions
- in matrix - Osteoblast = making
—> secretes osteoid —> catalyses
mineralisation
- in growing periosteum + endosteum - Osteoclast = breaking
—> dissolves bone —> resorb via
phagocytosis
- from bone marrow
- in bone surface (old/injured/excess)
What are the 2 pathways of bone development in utero?
- Intramembranous
- flat bones: skull, clavicle, mandible
- mesenchymal cells —> bone
- Endochondral
- long bones, ribs, vertebrae
- mesenchymal —> cartilage —> bone
- takes longer
How does intramembranous ossification occur? (5)
- Mesenchymal cells differentiate to osteoblasts
- Osteoblasts secrete osteoid —> trapped —>
become osteocytes - Osteocytes cluster —> ossification center
- Ossification centers fuse —> form trabecular matrix
(branches) and periosteum (outer membrane) - Blood vessels between cavities in cancellous bone
—> bring mesenchymal cells —> red marrow
How does endochondral ossification occur?
- Bone collar forms around hyaline cartilage
- Cavity forms in centre of cartilage —> periosteal
bud invades cavity - Spongy bone formed in cavity (primary ossification
= diaphysis) —> grows —> elongation - Medullary cavities form at ends of bone —> bone
formation (secondary ossification = epiphyseal) - Growth till cartilage only at ends —> articular
cartilage
What are the 2 categories of bone?
- Immature = first bone produced
- woven structure —> weaker - Mature = mineralised
- lamellar structure —> stronger
- cortical or cancellous
What are the 2 types of mature bone?
- Cortical —> compact and dense (outer)
- suitable for weight bearing - Cancellous —> spongy (inner)
What is the organisation of cortical bone? (5)
Composed of osteons compact together
- Haversian Canal —> central space
- contains blood vessels, nerves,
lymphatics
- Lamellae —> concentric layers around centre
- Lacunae —> small spaces between lacunae
- contain osteocytes
- Canaliculi —> tunnels connecting lacunae
- contain ECF
- Volkmans Canals —> transverse canals connecting
Haversian Canals
What are the 3 mechanisms of bone fracture?
- Trauma - high or low energy
- Stress - abnormal stress on normal bone
- Pathological - normal stress on abnormal bone
What is the structure of long bones?
Top to bottom:
1. Epiphysis
2. Physis
3. Metaphysis
4. Diaphysis
Outer to inner:
1. Periosteum = connective tissue membrane covering
2. Outer cortex = cortical bone
3. Cancellous bone —> red marrow in spaces
4. Medullary cavity —> yellow marrow
+ nutrient artery
+ articular cartilage at joint ends
What is the role of bones in calcium homeostasis?
Stores 99% of bodies calcium
- Calcium hydroxyapatite
- Store + release —> regulated by PTH, calcitriol,
calcitonin, vitamin D
What are the 2 types of bond growth?
- Interstitial —> length
- Appositional —> thickness (intermembranous)
What is interstitial bone growth?
Bone lengthening
- at physis:
epiphyseal side —> hyaline cartilage dividing to form
more matrix
diaphyseal side —> cartilage calcifies —> dies —>
replaced by bone
What is appositional bone growth?
Bone thickening (deposition beneath periosteum)
1. Periosteal blood vessel through ridge
2. Periosteal ridges fuse —> endosteum-lined tunnel
3. Osteoblasts in endosteum build new concentric
lamellae towards tunnel —> new osteon
4. Osteon grows outwards —> bone grows
5. Osteoclasts resorb old/damaged bone
- happens to 5-10% bone each year
What are the 4 stages of fracture healing?
What are the 6 causes of pathological fractures?
What are the 3 mechanisms of bone fracture?
How do stress fractures occur?
Bone overused —> stress > remodelling capacity —> weakened bone —> fractures easily
- usually to weight-bearing bones:
femur, tibia, metatarsals, navicular
- activity related:
athletes, occupation, military etc.
female athlete triad —> eating disorder,
amenorrhea, osteoporosis
What are the 6 causes of pathological fractures?
- Osteoporosis/osteopenia:
- osteoclast > osteoblast activity —> bones soft —>
low energy trauma fractures (fragility) - use T-score —> normal > -1
—> -1 > osteopenia > -2.5
—> -2.5 > osteoporosis - female:male —> 4:1
- causes: postmenopausal
senile
secondary —> hypogonadism, excess
glucocorticoid, alcoholism
- osteoclast > osteoblast activity —> bones soft —>
- Malignancy:
- primary —> osteosarcoma
—> chondrosarcoma
—> ewing sarcoma
—> lymphoma - bone metastasis —> blastic: prostate
—> lytic: kidney, thyroid, lung
—> both: breast
- primary —> osteosarcoma
- Vitamin D deficiency:
- inadequate calcium + phosphate —> insufficient
matrix mineralisation
—> rickets (children)
—> osteomalacia (adults)
- inadequate calcium + phosphate —> insufficient
- Osteomyelitis
- Osteogenesis Imperfecta (Brittle Bones)
- produce abnormal type I collagen —> insufficient
osteoid production - hereditary
- produce abnormal type I collagen —> insufficient
- Paget’s Disease
- excessive bone breaking
- 4 stages: osteoclastic activity
mixed osteoclastic-osteoblastic activity
osteoblastic activity
malignant degeneration
What are the 4 stages of fractures healing?
- Bleeding
- Inflammation
- haematoma forms, cytokines released,
aniogenesis, granulation tissue formed
- haematoma forms, cytokines released,
- New tissue formation
- soft callus (collagen —> type II collagen) to …
hard callus (bone —> type I collagen) - involves: fibroblasts, osteoblasts, chondroblasts
- soft callus (collagen —> type II collagen) to …
- Remodelling
- callus responds to activity —> excess removed
- involves: macrophages, osteoclasts, osteoblasts
What is Wolff’s Law?
Bone grows and remodels in response to the forces placed on it
