Bone Resorption

How long does the bone remodeling process typically take?

3 weeks to 3 months

What type of cells are present on the resting bone surface before remodeling begins?

Lining cells

What type of bone cell is embedded within the bone matrix?

Osteocyte

What type of precursor cell gives rise to osteoclasts?

Osteoclast precursor

At what point in the process does bone resorption occur?

At the activation stage

Which type of bone cell actively breaks down bone matrix?

Osteoclast

hat is the function of the reversal phase in bone remodeling?

It transitions from bone resorption to bone formation by signaling osteoblast precursors.

What type of cells appear near the cement line before new bone formation begins?

Osteoblast precursors

What is the initial unmineralized bone matrix secreted by osteoblasts called?

Osteoid

What cells are responsible for bone formation?

Osteoblasts

What is the term for the coordinated action of bone cells during remodeling?

Bone remodeling unit

hat process follows the deposition of osteoid to strengthen the newly formed bone?

Mineralization

Bone mass is _______ and changes based on _______

dynamic; loading

What is differential bone mass?

variation in bone density within an individual, often due to differences in mechanical loading

In which populations do you see differential bone mass

commonly seen in athletes who use one limb more than the other

What happens to the bone matrix over time?

The bone matrix accumulates damage over time due to mechanical stress

What type of microscopic damage occurs in bone from normal activities like walking?

Small cracks called micro-damage

What can happen if micro-damage in the bone matrix is not repaired?

It can accumulate to the point where the bone fails

How does bone remodeling help maintain bone integrity?

allows bone to adapt to mechanical load and repair accumulated damage

What technique is used to study osteocyte connections and signaling?

Osteon confocal microscopy

How are neighboring osteocytes connected?

They are connected by gap junctions, allowing them to share intracellular materials and signaling molecules

What allows osteocytes to communicate with each other?

Plasma membrane projections extending through canaliculi and connecting via gap junctions

How do osteocytes respond to mechanical forces or damage?

signals neighboring osteocytes, triggering a coordinated response

What is the first phase of bone remodeling?

activation

What molecules do osteocytes and osteoblasts secrete to regulate osteoclast activity?

RANKL (stimulates osteoclast differentiation) and OPG (suppresses osteoclast differentiation)

What is the function of RANKL in bone remodeling?

RANKL promotes osteoclast differentiation, initiating the bone resorption process

How do osteocytes initiate the remodeling process?

By increasing RANKL secretion, which stimulates osteoclast differentiation and bone resorption

What is osteopetrosis (marble bone disease)?

A disorder caused by impaired osteoclast activation, leading to excessive bone density

What happens to bone in osteopetrosis?

Abundant woven bone accumulates due to the absence of functional osteoclasts, preventing normal bone resorption

How does osteopetrosis affect bone remodeling?

Without functional osteoclasts, old bone is not resorbed, leading to overly dense but brittle bones

what is osteopetrosis

marble bone disease

What is the second phase of bone remodeling?

resorption

Which cells are responsible for bone resorption?

Osteoclasts

What stimulates osteoclast maturation and activity?

RANKL (Receptor Activator of NF-κB Ligand

How do osteoclasts break down bone?

They form tight attachments to the bone surface, create a resorptive space, and secrete acid and proteases to digest bone mineral and proteins

Which enzymes are used by osteoclasts to acidify the resorption space?

Carbonic anhydrase and vacuolar ATPase

What happens to the bone components after resorption?

The digested mineral and protein components are released into the extracellular space

What is the third phase of bone remodeling?

reversal

What happens to osteoclasts during the reversal phase?

numbers decrease as resorption slows down

ow does the reversal phase prepare for bone formation?

Osteoclasts release factors that stimulate osteoblast differentiation and activity

hat type of cells are recruited during the reversal phase?

Osteoblast precursors

What is the fourth phase of bone remodeling?

formation

What type of matrix do osteoblasts produce during the formation phase?

A type I collagen matrix called the osteoid

What additional role do osteoblasts play besides producing osteoid?

secrete osteoblast-stimulating factors that embed in the matrix, preparing for future remodeling

What is the final step in the formation phase of bone remodeling?

Mineralization

What is the progression of cells leading to an osteocyte during mineralization?

Mesenchymal stem cell → Preosteoblast → Osteoblast → Osteoid osteoblast → Mineralizing osteocyte → Osteocyte

What is the final phase of bone remodeling?

quiescence

What do osteocytes secrete to inhibit bone remodeling?

Osteoclast and osteoblast inhibitory factors

What is a major inhibitor of osteoblast activity?

Sclerostin

How does sclerostin expression change as osteoblasts become osteocytes?

increases

When does bone remodeling resume after quiescence?

When new stress or damage is detected

What is sclerosteosis?

disease caused by the loss of sclerostin, leading to excessive bone formation

What is the main characteristic of sclerosteosis?

global progressive increase in bone density

What are potential complications of sclerosteosis?

Loss of hearing, sight, or smell due to cranial nerve compression, and possible sudden death due to brainstem compression

What is the inheritance pattern of sclerosteosis?

Autosomal recessive

How does Toll-like receptor signaling affect osteoclastogenesis?

promote and enhance osteoclast differentiation

What is used to stain osteoclasts in bone tissue studies?

TRAP staining (Tartrate-Resistant Acid Phosphatase)

How does bacterial lipopolysaccharide (LPS) affect osteoclast differentiation?

LPS enhances osteoclast differentiation in RANKL-committed precursors

How does periodontitis affect bone remodeling?

romotes osteoclast differentiation, leading to alveolar bone loss

What is a consequence of alveolar bone loss in periodontitis?

result in tooth instability and eventual tooth loss

How can dental plates help after tooth loss?

can restore function by replacing missing teeth

How do natural teeth interact with alveolar bone differently from dental plates?

Natural teeth extend into the alveolar bone and translate mechanical forces from chewing, while non-implanted dental prosthetics rest on the bone surface and do not transmit forces