Week 9 - Bone Formation and Resorption Flashcards
What is the alveolar bone also known as?
Cribiform plate or bundle bone
How is the cribiform plate formed?
as a result of attachment of the PDL fibers and passage of vessels and nerves into and out of the PDL
What is the term bundle bone referred to?
bone in which Sharpey’s fibers (PDL) are embedded
What is woven bone?
immature/newly formed bone in which the collagen fiber matrix is randomly oriented
What is woven bone associated with?
generally newly formed (embryologic development) or associated with healing wounds
How does woven bone compare to mature bone?
- Has more cells per unit area
- Contains a greater volume of non-collagenous protein
- Forms more rapidly than mature bone
What is lamellar bone?
mature/secondarily formed bone
What can lamellar bone be classified as?
Spongy/cancellous and compact/cortical
What is spongiosa/cancellous bone?
trabecular bone that lies between the cortical plates and within the marrow spaces
Describe the appearance of spongiosa/cancellous bone
- Trabeculae lined with osteoblasts (bone lining cells)
- Has random orientation of collagen fibers
What are facial and lingual cortical plates made of?
Made up of lamellar bone, haversian bone, or interstitial bone
What is the composition of bone?
67% inorganic (Calcium hydroxyapatite)
33% organic
- 28% collagen
- 5% proteins (osteocalcin, sialoprotein, osteonectin, BMP)
What is osteoid?
bone matrix formed by osteoblasts (5-10 um increments)
What is the function of osteoblasts?
Make bone (active bone lining cells)
What is the function of osteoclasts?
Remove bone
What is an osteocyte?
An osteoblast that has been entrapped by its own osteoid matrix
What are bone lining cells?
Flattened inactive osteoblasts that line trabecular bone. Protect bony surface from osteoclast activity
What are chondroblasts?
Lay down cartilage
What are chondrocytes?
Maintain ECM and produce cartilage matrix
What are mesenchymal cells?
Undifferentiated cells
What are canaliculi?
how osteoblasts and osteoclasts communicate with the outside environment
What is the process of communication of canaliculi?
Processes of the osteocytes travel within the canaliculi and connect to other osteocytes/osteoblasts, allowing cell-to-cell communication
What other properties can the canaliculi have?
Mechanoreception
What is the periosteum?
A dense connective tissue, bound to bone by Sharpey’s fibers, that contains blood vessels, nerves, and three cell layers
What are the three cell layers of the periosteum?
- Peripheral cell layer of fibroblasts
- Intermediate cell layer of undifferentiated mesenchymal cells
- Proximal cell layer of osteoblasts
What is the PDL a modified version of?
Modified version of a periosteum
What does the endosteum line?
the medullary cavity and cancellous bone (trabeculae)
What is the endosteum similar in composition to?
Generally has the same composition as periosteum but is significantly thinner
What are collagen proteins associated with bone?
Type I
Type II
Type III
Type V
Type X
What is the function of type I protein?
fibrillar; ubiquitous in distribution (located everywhere)
What is the function of type II protein?
fibrillar; primarily a cartilage protein. Found in endochondral bone formation
What is the function of type III protein?
fibrillar; granulation and mesenchymal tissues. Found in healing tissues
What is the function of type V protein?
fibrillar, stromal connective tissue. Promotes cellular attachment and migration
What is the function of type X protein?
growth plate; facilitates conversion of cartilage -> bone
What are non-collagenous proteins associated with bone?
osteonectin, osteopontin, osteocalcin, BMP and others
What are non-collagenous proteins associated with bone characterized by?
(all have these properties)
- Highly acidic nature
- High aggregation tendencies
- Calcium binding properties
What does bone formation consist of?
- in-situ remodeling
- intramembranous bone formation
- endochondral bone formation
What is in-situ remodeling?
a process of osteoclastic resorption, and bone replacement by osteoblast activity
Where is in-situ remodeling mostly seen in?
Areas of alveolar bone affected by orthodontics
What are the steps of in-situ remodeling?
Osteoclasts resorbs bone
Osteoblasts get stimulated and release osteoid
Osteoid gets mineralized and new bone is formed
What is intramembranous bone formation?
bone formation within or between connective tissue membranes consisting of type I collagen (connective tissue framework that gets calcified)
What does bone NOT replace?
Cartilage
Where is intramembranous bone formation found in?
the inner spongy layers of bone, as well as sutures
Describe intramembranous bone formation as a method of bone deposition
It is an extremely rapid and disorganized method of bone deposition, and allows for growth of the tissues surrounding it
What is an example of intramembranous bone growth?
Woven bone is an example of intramembranous bone growth -> healing response
What do osteoblasts secrete?
Osteoblasts secrete matrix vesicles that mineralize surrounding collagen fibers
How are osteocytes created?
The osteoblasts usually become trapped themselves, becoming osteocytes
What do matrix vesicles contain?
contain pyrophosphatase, **alkaline phosphatase (helps mineralize collagen), glycoproteins, phosphoproteins, phospholipids
What is endochondral bone formatino?
bone formation within hyaline cartilage that involves a concomitant replacement of the cartilage framework by bone
What type of bone formation does bone replace cartilage?
Endochondral bone formation
Where is endochondral bone formation found in?
vertebrae, long bones, base of the skill, and head of the mandible
What is the process of endochondral bone formation?
- Mesenchymal cells create a general outline/shape of what the final bone will look like
- Cells differentiate into chondroblasts (cartilage cells), which increase in size, secrete collagen, and mineralize it with matrix vesicles
- The newly formed chondrocytes eventually die - Vascular tissue from surrounding perichondrium invades cartilage, allowing chondrocytes/chondroclasts and mesenchymal cells to enter the area
- Chondroclasts eat away the cartilage, and newly differentiates osteoblasts deposit osteoid into the cartilage
- Osteoid is mineralized by osteocytes, and bone is made
What are growth of endochondral bones dependent on?
the growth of the cartilage and stops once the cartilage has been completely removed
What are the zones of cellular activity?
- reserve or resting chondrocytes
- proliferation
- maturation
- hypertrophy and calcification
- cartilage degeneration
- osteogenesis
What kind of cartilage is in the reserve or resting chondrocytes?
Hyaline cartilage
What happens during proliferation?
Collagen starts to form
What happens during maturation?
less division of cells but chondrocytes are increasing in size
What happens during hypertrophy and calcification?
where areas become evaluated (look more empty, have larger spaces)
What happens during cartilage degeneration?
Chondrocytes die
What happens during osteogenesis?
osteoblasts come in with capillaries. Osteoblasts differentiate and bone formation occurs
What is bone metabolism controlled systemically by?
Hormones
What is bone metabolism controlled locally by?
Mechanical factors, growth factors, and cytokines
What are hormones important for?
Bone metabolism
- affect absorption both directly and indirectly
- Can cause both absorption or formation depending on concentration and synergy/interactions with each other
What are examples of hormones that are important to bone metabolism?
Parathyroid hormone (PTH), 1,25-dihydroxyvitamin D, Calcitonin, Estrogen, Glucocorticoids
What do cytokines and growth factors cause?
osteoblasts to stimulate formation of osteoclasts. Indirectly causes bone resorption
What are examples of cytokines and growth factors important to bone metabolism?
Interlukin-1, interlukin-6, BMP-2 and BMP-7, TRF, IGF, FGF, Platelet-derived GF)
What happens under conditions that favor bone resorption?
Osteoblasts can be stimulated by cytokines and hormones to produce interlukin-6 which promotes differentiation of osteoblasts
Describe osteoclast mediated resorption
Chemicals “wake up” osteoblasts which activates osteoclast precursors and allows activation of osteoclasts (which resorb bone)
What does osteoclastic resorption of bone do?
(works like a bacteria) decreases pH to demineralized hydroxyapatite
What enzymes work in osteoclastic resorption to degrade the bone matrix and demineralize hydroxyapatite?
lactic acid, citric acid, free protons/H+, **acid phosphatase, aryl sulfatase, collagenase and gelatinase
What is the osteoclast mediated resorption reaction?
CO2 + H2O -> HCO3- + H+
- Carbon dioxide and water catalyzed by carbonic anhydrase. Results in bicarbonate and free protons
- Bicarbonate gets removed and free protons are there to help demineralize and break down the bone
