Bone and Cartilage Flashcards
Intramembranous Ossification
bones of skull, face, and clavicle
- Ossification center forms in fibrous connective tissue and the mesenchymal cells mature into osteoblasts
- Osteoblasts secrete osteoid which is mineralized and osteoblasts become osteocytes
- Osteoid is about embryonic blood vessels and form trabeculae with periosteum surrounding it
- Bony collar forms and red marrow appears
- Appositional growth and remodeling will change the bone with age
Endochondrial Ossification
bone replaces cartilage model
- Formation of bony collar around cartilage
- Cavitation of hyaline cartilage within the cartilage model
- Chondrocytes enter forming bone and hypertrophy and calcify (not ossify like in intramembranous)
- Chrondrogenic cells become osteoprogenitor cells which then become osteoblasts to secrete osteoid
- Invasion of cavities by periosteal bud and spongy bone forms because bony collar prevents nutrients from supplying chondrocytes, which die and form spongy bone
- Formation of medullary cavity as ossification continues and secondary ossification center appears in epiphysis (no bony collar at epiphysis)
- Ossification of epiphysis with growth plate still consisting of hyaline cartilage
Calcium is Required for Several Processes
Cell division Blood coagulation Gland and nerve cell secretions Nerve impulse transmission Muscle contraction
Role of RANK L
Osteoclasts have RANK ligand receptors and when RANK binds it promotes bone resorption
Osteoblasts secrete OPG, which bind to RANK ligands to inhibit binding onto RANK L receptors on osteoclasts in order to promote bone formation
When bone formation occurs, bone lining cells move and expose the bone and become osteoblasts and begin expressing RANK ligand, which binds to RANK on osteoclast precursors
RANK L binds to RANK to allow for bone resorption
Then osteoblasts form the bone for remodeling
OPG blocks RANK L binding to RANK receptors on osteoclasts and estrogen limits the amount RANK L expression by osteoclasts = regulators
Wolff’s Law
Wolff’s law – A bone grows/remodels in response to forces or demands placed upon it
Long bones are thickest midway along the shaft (where bending stress is greatest)
Curved bones are thickest where they are most likely to buckle
Bony trabeculae form along lines of stress
Large, bony projections occur where active, robust muscles attach
Basic Multicellular Unit (BMU)
Head of osteoclasts
Tail of capillaries, progenitor cells, and osteoblasts
Releasing H+ and breaking down mineral components and other organic components so that remodeling can occur
Nerves and osteoprogenitor cells to turn into osteoblasts that secrete matrix then turn into osteocytes
1-4 transverse cuts show the layers and cells that are present during this process
Remodeling Time
I & II = Resorption of bone; 42 days
III to V = Formation of new bone; 22 days
IV = Mineralization lag time; 130 days
Around 192 days
Microfractures
Small cracks within bones - occur all the time
Can accumulate faster than normal remodeling can take care of them = Stress fracture
Nondisplaced vs. Displaced
Nondisplaced – bone ends retain normal position
Displaced – bone ends are out of normal alignment
Complete vs. Incomplete
Complete – bone is broken all the way through
Incomplete – bone is not broken all the way through
Linear vs. Transverse
Linear/longitudinal –fracture is parallel to long axis of bone
Transverse –fracture is perpendicular to long axis of bone
Simple vs. Compound
Simple (closed) – bone ends do not penetrate the skin
Compound (open) – bone ends penetrate the skin
Name a common bone broken in those under 75 years of age?
Distal Radius = Colle’s fracture
Communited vs. Compression
Communited: brittle bones mostly in elderly people or osteogenesis imperfecta; bone fragments into three or more pieces
Compression: bones are crushed during a fall for example; bone is crushed
Greenstick vs. Depressed
Greenstick: mostly in children because still isn’t completely calcified; bone breaks incompletely
Depressed: broken bone portion is pressed inward; typical of skull fracture
Spiral vs. Epiphyseal
Spiral: most common in sports injuries; ragged break occurs when excessive twisting forces are applied
Epiphyseal: cartilage cells are dying and area is weaker; epiphysis separates from diaphysis along epiphyseal plate
Salter Harris Fractures
30% are associated with growth disturbance
2% result in disability
Mainly lower extremity due to weight bearing
Epiphyseal plate can be affected/fractured
Salter Harris I
Point tenderness over physeal plate
X-rays initially often appear normal
One week later, films may show sclerosis relating to new bone reparative process
Good prognosis
Salter Harris II
Fracture through growth plate and metaphysis
Most common SH fracture
May produce long bone shortening
Most significant if in the lower extremity
Salter Harris III
Fracture through epiphysis and growth plate
Notice physeal widening
Prone to chronic disability because of articular involvement
Salter Harris IV
Fracture affects epiphysis, metaphysis and growth plate
Prone to chronic disability because of articular involvement
Salter Harris V
Compression or crush injury of growth plate
X-rays initially normal
Early closure of the growth plate
Poorer prognosis due to shortening and/or angulation
Bone Repair Steps
- Torn blood vessels hemorrhage, a mass of clotted blood (hematoma) forms at fracture site, site becomes painful, swollen, and inflamed
- A few days after the fracture, a soft callus of highly vascular collagenous tissue (granulation tissue) is formed and capillaries grow into tissue and debris is cleared away by phagocytic cells
- New bony trabeculae appear within fibro-cartilaginous callus; fibrocartilaginous callus is converted into a bony callus; bony callus appears 3-4 weeks post-injury, continues until bones are firmly united 2-3 months later
- Bone Remodeling: Excess bone is removed along the exterior of the shaft and in the medullary cavity; compact bone is deposited, reconstructing walls of the shaft
Fibrocartilaginous Callus Formation
Osteoblasts and fibroblasts migrate to the fracture and begin reconstructing bone
Fibroblasts secrete collagen fibers that connect broken bone ends
Osteoblasts begin forming spongy bone
Osteoblasts furthest from capillaries secrete an externally bulging cartilaginous matrix that later calcifies
Bone Repair Process
The bone repair process is a combination of intramembranous and endochondral bone formation, coordinated with remodeling and resorption
Cancellous Bone
(a.k.a. spongy, trabecular, medullary)
lined by endosteum with osteoprogenitor cells, osteoblasts and osteoclasts present
Haversian systems generally absent; osteocytes communicate with blood sinusoids in the marrow cavity via canaliculi
Found in medulla of membrane bones, ends of long bones, and filling center of irregular bones
Woven Bone
(a.k.a. primary, immature)
No lamellar organization
First bone laid down, and also found during fracture healing and at some tendon attachments
Attach tendon to bone
Sharpey’s Fibers
Attach other tissues to bone
Muscle to bone
Play large role in attaching the periodontal ligament and bone of tooth
Hyaline Cartilage
Hyaline (clear; blueish in gross section)
Embryonic skeleton & portions of adult
Respiratory tree, nasal region, costal cartilages
Articular cartilage
Type II collagen
Diffuse fibers throughout matrix; amorphous
Normally surrounded by perichondrium
Outer fibrous layer
Inner chondrogenic layer
Exception - articular cartilage
Repair of Cartilage
Not highly vascularized therefore hard to repair
Not innervated
Avascular
No lymphatic drainage
Receives nutrients by diffusion via surrounding connective tissue
Elastic Cartilage
Elastic (yellowish in gross section)
Places needing structure and flexibility
Epiglottis, larynx, pinna (cauliflower ear if damaged), eustacian tube
Type II collagen + elastic fibers
Diffuse fibers throughout matrix; amorphous
Surrounded by perichondrium
Fibrocartilage
Resists both compressive and shear forces
Pubic symphysis, menisci, intervertebral disks
Type I collagen
Thick bundles very obvious in matrix
Fewer chondrocytes than others
No perichondrium
Common injury = herniated disc
Bone Lining Cells
Line the surface of bone (very spindle shaped)
Derived from osteoblast precursors or osteoblasts
Communicate with osteocytes via canaliculi
Serve as an ion barrier and appear to facilitate signaling for bone resorption and remodeling
