Ch. 6: Bone & Skeletal Tissue
Skeletal Cartilages
Classification of Bones
Functions of Bones
Bone Structure
Development
Bone Homeostasis: Remodeling & Repair
Homeostatic Imbalances of Bone
Developmental Aspects
Ch. 6: Bone & Skeletal Tissue
Skeletal system includes bone & cartilage
Skeletal Cartilages
Structure, types, locations
All types of sk cart have chondros, extracell mtx, fibers
Hyaline c
most common, flexible, resilient, contain fine collagen fibers
Articular, costal, respiratory (vb), nasal (ext nose)
Elastic c
like hyaline; more elastic fibers; tolerate repeated bending; epigolttis, ext ear
Fibrocart
Cross between hyal cart (chondros) & dense reg conn tiss (thick coll fibers);
high tensile strength
Resist high pressure & stretch
Menisci in knees, intervert discs
Growth
Appositional; Interstitial
Figure 6.1
Ch. 6: Bone & Skeletal Tissue
Classification of Bones
Axial vs appendicular
By shape: long, short, flat, irregular
Functions of Bones
Support
Protection
Movement
Storage of minerals, growth factors, fat
Hematopoesis
Forces
• Tension
• Compression
• Bending
Figure 6.2
Ch. 6: Bone & Skeletal Tissue
Bone Structure
Gross Anatomy
Bone Markings – See Table 6.1
Texture
Compact (lamellar): dense outer layer, naked eye smooth
Spongy (cancellous): trabeculae, red or yellow marrow
Typical long bone structure
Diaphysis: compact bone collar over marrow-filled medullary cavity
Epiphyses: bone ends, compact over spongy, articular (hyaline) cartilage;
epiphyseal line (remnant of epiphyseal plate)
Membranes: periosteum, endosteum, osteoblasts/clasts
Short, irregular, flat bone structure
Compact over spongy; no marrow cavity
Hematopoetic tissue (red marrow):
Trabecular parts of long bones (esp. heads of femur, humerus in adult) &
flat bones
Microscopic Anatomy
Chemical Composition
Table 6.1
Table 6.1
Figure 6.3
Figure 6.3a
Figure 6.3b
Figure 6.3c
Figure 6.5
Ch. 6: Bone & Skeletal Tissue
Bone Structure
Gross Anatomy
Microscopic Anatomy
Cell types: osteogenic, osteoblasts, osteocytes, osteoclasts
Compact bone
Microscopic passageways; osteons (Haversian systems)
Multiple lamellae per osteon; alternating collagen fiber orient’n
Central canal; osteocytes btn lamellae
Spongy bone
Trabeculae align with stress; no osteons
Chemical Composition
(skeleton = 14-17% of total adult body weight i.e. ~ 10 kg)
Organic
Cells & osteoid (ground substance & collagen fibers)
Inorganic (2/3 of skeleton weight – Trotter & Peterson, J Bone Jt Surg Am 1962)
Hydroxyapatite crystals (mainly calcium phosphate) (40% of
hydroxyapatite is Ca; total body Ca ~ 2.5 – 3 kg for normal 70 kg person)
Figure 6.6
Bone architecture
(a) macroscopic bone,
(b) osteons with circular arrangements of differently
oriented collagen fibers.
(c) collagen fiber = bundles of collagen fibrils.
(d) collagen fibril = staggered arrangement of collagen
molecules with embedded mineral crystals (blue).
(e) collagen molecule triple helix.
Collagen: tensile and bending strength.
Hydroxyapatite (calcium phosphate):
compressive strength
Reinforced concrete
“Rebar” (steel reinforcing bars): tensile
and bending strength.
Concrete:compressive strength.
Above: channel.nationalgeographic.com/series/la-hardhats/all/Photos#tab-Photos/11
Left: www.bnl.gov/nsls2/sciOps/chemSci/softMatter.asp
College or Department name here
Figure 6.6
Figure 6.6a
Figure 6.6b
Figure 6.6c
Ch. 6: Bone & Skeletal Tissue
Development
Ossification (= osteogenesis)
Forming the bony skeleton
Intramembranous ossif
Endochondral ossif
Postnatal bone growth
Length of long bones: epiphyseal plate
Hormonal regulation
GH. Sex hormones: growth spurt, epi plate closure
Figure 6.8.
Figure 6.8
Figure 6.9
Figure 6.10
Figure 6.11
Figure 6.15
Ch. 6: Bone & Skeletal Tissue
Bone Homeostasis: Remodeling & Repair
Remodeling
At periosteum & endosteum
Remodeling unit w/ osteoblasts, osteoclasts
Osteocytes (stimulated by osteoblasts) secrete matrix
Control of remodeling
By hormones to regulate plasma [Ca]
PTH ↑when [Ca] ↓, stimulates osteoclasts
In response to mechanical stress
Bone strongest where stress acts
Long bone hollow ctr; shaft thickest at middle
Curved bones thickest where most likely to break
Spongy bone trabeculae line up along stress lines
Projections (tuberosity, crest,…) where muscles attach
Ch. 6: Bone & Skeletal Tissue
Bone Homeostasis: Remodeling & Repair
Remodeling animation with description of osteoporosis (54 s):
http://www.youtube.com/watch?v=5uAXX5GvGrI
Figure 6.12
Figure 6.13
Ch. 6: Bone & Skeletal Tissue
Bone Homeostasis: Remodeling & Repair
Repair
Classification of fractures
Bone end positions: displaced or nondisplaced
Complete or incomplete
Orientation: linear (long axis) or transverse
Skin penetration: open (compund) or closed (simple)
By nature, location of break – see Table 6.2
Repair process – see Fig 6.15
Table 6.2
Table 6.2
A current debate: Do some osteoporosis drugs increase the
rate of “rare” fractures?
Radiograph Showing a
Subtrochanteric Stress Fracture.
Kwek et al., NEJM 359:316, 2008.
Not the most common site for stress fracture.
Common stress fracture sites: tibia (runners),
metatarsals (dancers, skaters), fibula…) From
article about possible increase in fracture risk in
patients on bisphosphonates (osteoporosis drugs).
See also JAMA 305: 783-789, 2011.
Some data suggests that the risk of rare fractures
is a lot higher after 6-8 years on bisphosphonates
than after 2 yrs; some suggest a bisphosphonate
holiday after 5 yrs (NYT 2011-03-06).
Figure 6.15
Ch. 6: Bone & Skeletal Tissue
Homeostatic Imbalances of Bone
Osteomalachia
Failure to mineralize; weak bones
Rickets in children
Due to Ca deficiency, maybe secondary to vit D deficiency
Osteoporosis
Resorption > formation; ↓ bone density, mass
Elderly susceptible; vertebral, femoral neck fx
Estrogen, testosterone slow osteoclasts, stimulate blasts
Post-menopausal fall in estrogen
Remodeling animation with description of osteoporosis (41 s):
http://www.youtube.com/watch?v=NKVKNqIOnh0&feature=related
Paget’s disease
Disorganized (Pagetic) bone; spongy/compact too high
Elderly susceptible; affected bone weak
Figure 6.16
Hip Fractures
•
300,000 hip fractures annually in US
• Majority related to osteoporosis and falls in older people
• Enormous public health implications and economic burden
• A top cause of immobilization in elderly
• Patients who have sustained a hip fracture
• 2-year mortality rate of 36%
• Immobility → increased bone resorption, predisposition to 2nd hip fracture
• Many don’t regain prefracture level of mobility; lose independence, QOL
• Risk of subsequent skeletal fracture up 2.5x
• Risk of new hip fracture up 5x – 10x
Editorial: Calis KA, Pucino F, NEJM 2007: Sep 17, epub ahead of print
Drug therapy for osteoporosis
Ca, Vitamin D supplementation
Bisphosphonates
Many have names ending in –dronate
Fosamax/alendronate, Actonel/risedronate, etc.
Reduce activity of osteoclasts
Reduce bone remodeling
Side effects: osteonecrosis of jaw, uncommon fractures,
etc.
PTH analogs
Forteo/teriparatide
34 aa fragment of PTH (84 aa)
Mechanism of action mysterious
College or Department name here
Further reading:
NYTimes Sep 23 2009
Can vitamin D improve athletic performance?
http://well.blogs.nytimes.com/2009/09/23/phys-ed-can-vitamin-d-improve-your-athletic-performance/
Vitamin D essential for absorption of Ca from gut; it also helps other cells
including muscle cells use Ca. Many of us with a “normal” diet and occasional
outdoor time are vitamin D deficient and we may benefit from more D.
Vitamin D Status and Its Relation to Muscle Mass and
Muscle Fat in Young Women. 59% of sample (16-22 yo ♀ in Calif)
had insufficient 25OH-D (<30 ng/ml), including 24% who were deficient in
25OH-D (<20 ng/ml) (surprisingly large %). Vitamin D insufficiency was
associated with increased fat infiltration in muscle.
Gilsanz, …, Kremer. J Clin Endocrinol Metab 2010; DOI: 10.1210/jc.2009-2309
Further reading:
NY Times Sep 1 2009
Does ibuprofen help or hurt during exercise?
http://well.blogs.nytimes.com/2009/09/01/phys-ed-does-ibuprofen-help-or-hurt-during-exercise/
Many athletes regularly take ibuprofen. Article describes increasing evidence
that "vitamin I" has negative side effects including blunted growth response of
bone to applied stress, decreased post-workout collagen production, etc. One
scientist wrote recently in Brit J Sports Med that regular ibuprofen use around
the time of exercise diminishes the expected increase in skeletal strength that
otherwise comes from exercise. http://bjsm.bmj.com/cgi/content/full/43/8/548