What are the characteristics of immature bone?
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It has more cells and the matrix is not lamellar.
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What are the characteristics of immature bone?
It has more cells and the matrix is not lamellar.
What is the periosteum made of?
An outer fibrous layer and an inner cellular layer containing osteoprogenitor cells.
What is the role of Vitamin D in the body?
Essential for calcium absorption and bone mineralization.
What is the function of osteoclasts?
To resorb bone tissue by releasing protons and lysosomal hydrolases into the extracellular space.
What type of cell is responsible for bone resorption?
Multinucleated cell known as osteoclasts.
What are osteoprogenitor cells difficult to distinguish from at the microscopic level?
Bone-lining cells, also known as endosteal cells.
What are osteons or Haversian systems made of?
Cylindrical units.
What are the spaces within the bone matrix called?
Lacunae (singular: lacuna).
What are bone-lining cells derived from?
Osteoblasts.
What is another name for Volkmann's canal?
Volkmann canal.
How is osteomalacia different from osteoporosis?
Osteomalacia is a problem with bones not hardening due to impaired mineralization, while osteoporosis is the weakening of the bone resulting from low peak bone mass, increased bone resorption, and impaired bone formation.
What do osteoblasts secrete?
The extracellular matrix of bone.
What is the nature of the newly formed tissue during ossification?
An immature (woven) bone with thick trabeculae lined by osteoblasts and endosteal cells.
What occurs during further growth and remodeling of the bone?
Replacement of woven bone by the inner and outer layers of compact bone with spongy bone between them.
What is the name of the constricted microenvironment where osteoclasts release protons and lysosomal hydrolases?
Howship’s lacuna.
What is the function of Haversian canals?
They contain blood vessels and nerve fibers that nourish the bone cells.
What are the cells present in bone tissue?
Osteoblast, osteocyte, osteoprogenitor cells, bone lining cells, and osteoclast.
What do osteoblasts deposit during the initial stage of ossification?
Unmineralized bone matrix, the osteoid.
What is the function of Haversian canals?
They contain blood vessels and nerves for the osteons.
How do osteocyte processes communicate?
By gap junctions.
What does bone tissue depend on osteocytes for?
To maintain viability.
What are the three functional stages of an osteocyte?
a. Relatively quiescent osteocyte - Few rER and mitochondria, fills the lacuna. b. Formative osteocyte - rER, golgi, osteoid in pericellular space, arrow nonmineralized osteoid. Outer margin of lacuna is not present. c. Resorptive osteocyte (osteocytic remodeling) - The pericellular space is devoid of collagen fibrils. Outer boundary of lacuna.
What happens to osteocytes in mature bone during tissue preparation?
Osteocytes shrink and lacunae appear empty with a small nucleus attached to their walls.
How is mature bone tissue classified?
As compact (dense) or spongy (cancellous).
What forms the interior of the bone?
Sponge-like meshwork consisting of trabeculae (spongy bone).
What are the cells in the endosteum known as?
Endosteal cells.
What is the function of endosteum?
To line bone cavities and contain osteoprogenitor cells.
What are the characteristics of mature compact bone?
It contains several osteons with concentric lamellae, Haversian canals with blood vessels, nerve, and connective tissue.
What is contained within each lacuna?
A bone cell, or osteocyte.
What is the appearance of osteoclasts?
Large, multinucleated cells with acidophilic cytoplasm.
From which cells are osteoclasts derived?
Hemopoietic progenitor cells in bone marrow.
What is the role of osteoblasts in the bone remodeling unit (BRU)?
Depositing bone, beginning at the origin of the resorption canal.
What is osteoporosis characterized by?
Progressive loss of normal bone density.
What conditions can result from prolonged and severe vitamin D deficiency?
Rickets in children and osteomalacia in adults.
What is the pale area of newly secreted unmineralized material in osteoblast called?
Osteoid, which contains collagen fibrils.
What happens as osteoid undergoes mineralization during ossification?
Trapped osteoblasts become osteocytes.
What is the main function of osteoclasts?
Bone resorption (eating bone).
What is present in the lacunae?
Osteocytes.
How do bones appear on X-ray in individuals with osteopetrosis?
Bones appear dense on X-ray, but they are very fragile and break easily.
What is the uncalcified matrix of bone called?
Osteoid.
How do osteocyte processes communicate?
By gap junctions.
What are Volkmann's canals?
Channels in the bone that transmit blood vessels and communicate with the Haversian canals.
What is the major structural component of bone matrix?
Type I collagen.
From what type of tissue are all bones developed?
Mesenchyme (embryonic connective tissue).
What are the functions of bone tissue?
Support, protection, regulation of blood calcium and phosphate levels.
When does direct ossification of the mesenchyme begin?
In the fetal period.
What are the inner circumferential lamellae?
Layers of bone tissue that line the medullary cavity.
How are lacunae connected to each other?
By canaliculi.
What do osteoblasts secrete to constitute the initial unmineralized bone?
Bone matrix proteins, which form osteoid.
What is an osteocyte surrounded by when completely surrounded by osteoid or bone matrix?
Osteoid or bone matrix.
What are the channels that connect adjacent osteons and the Haversian canal?
Volkmann's canal
What is the thin, light-blue layer in the bone spicule called?
Osteoid (uncalcified matrix).
What is the appearance of the cytoplasm of osteoblast?
Markedly basophilic.
What are osteoprogenitor cells derived from?
Mesenchymal stem cells.
What are the cylindrical units in mature compact bone called?
Osteons or Haversian systems.
What forms the outside of the bone?
Compact, dense layer (compact bone).
What are osteoclasts responsible for?
Bone resorption and remodeling.
Do osteoclasts have PTH receptors?
No, osteoclasts do not have PTH receptors.
What are the structural units of compact bone?
Osteons
What is the outcome of the continued centripetal deposition of lamellae?
Creation of a new osteon.
What are the tiny channels that connect adjacent lacunae and allow osteocytes to communicate?
Bony canaliculi
What is the space between the lamellae known as?
Lacunae.
What is the function of interstitial lamellae?
They fill the spaces between osteons in compact bone.
What is the primary protein in bone, constituting 90% of the protein in bone?
Type I collagen.
What is created as a result of the deposition of bone by osteoblasts?
The 'closing end' of the BRU.
What are the concentric rings of the bone matrix called?
Lamellae
What does L.S. Ground bone refer to?
Longitudinal section of ground bone used for microscopic examination.
What is another name for nonlamellar bone?
Bundle bone or woven bone.
What are osteocytes referred to once surrounded by their secreted matrix?
Osteocytes.
What is the function of osteons?
They are the structural unit of compact bone, providing strength and support.
What is observed under the osteoclast as a result of its activity?
A shallow bay called a resorption bay (Howship’s lacuna).
How do patients with achondroplasia appear in terms of their limb bones?
Short and thick.
What is the central canal within the osteon called?
Haversian canal
What appears in the mesenchymal connective tissue during ossification?
An ossification center.
What is the characteristic feature of epiphyseal growth plates in patients with achondroplasia?
They exhibit a reduced zone of proliferation.
Where are osteoclasts seen in relation to bone resorption?
On the surface of bone where resorption is taking place.
What is the initial step in the bone remodeling unit (BRU)?
Osteoclastic erosion of bone in a 'resorption canal'.
Are Volkmann’s canals surrounded by concentric lamellae?
No, they are not surrounded by concentric lamellae.
What are the layers of bone matrix that run parallel to the bone surface?
Circumferential lamellae
What is C.S. decalcified bone?
Cross-section of bone from which the mineral content has been removed.
What are the two different processes of bone development?
Intramembranous ossification and Endochondral ossification.
What does the Haversian canal contain?
The vascular and nerve supply of the osteon.
When do cartilage models of bones form from mesenchyme?
During the fetal period.
What are the outer circumferential lamellae?
Layers of bone tissue that line the outer surface of compact bone.
What is the impact on the length of long bones in patients with achondroplasia?
Their length is shortened.
What is osteopetrosis?
A rare congenital disease characterized by increased bone density and defective osteoclast function.
What is the most important regulator of calcium and phosphate levels in the extracellular fluid?
Parathyroid hormone (PTH) secreted by the parathyroid glands.
What connects Haversian canals and the marrow cavity?
Perforating (Volkmann’s) canals.
What happens in the zone of proliferation during endochondral bone formation?
Cartilage cells undergo divisions and organize into distinct columns.
What happens in the zone of calcified cartilage during endochondral bone formation?
The hypertrophied cells begin to degenerate, and the cartilage matrix becomes calcified, serving as an initial scaffold for deposition of new bone.
What is the process called when osteocytes are responsible for remodeling of matrix?
Osteocytic remodeling.
What are the zones involved in endochondral bone formation?
What type of bone is stained dark blue in the bone spicule?
Osteocytes are embedded within the bone matrix and stained dark blue.
What does C.S. Decalcified refer to in bone structure?
It refers to a cross-section of bone tissue after removal of calcium salts.
What is the responsibility of osteoblasts in relation to bone matrix?
Osteoblasts are responsible for the calcification of bone matrix.
What are the remnants of old osteons that have been partially destroyed during bone remodeling?
Interstitial lamellae
From what type of cells are osteoclasts derived?
Mononuclear hemopoietic cells.
What are the small spaces within the bone matrix where osteocytes are located?
Lacunae
What is a bone remodeling unit (BRU)?
A two-stage process whereby cortical bone is remodeled from within.
What encloses the cell processes of osteocytes?
Canaliculi.
What key enzyme do osteocytes secrete for ECM remodeling?
Matrix metalloproteinases (MMPs).
What is the purpose of osteocytic remodeling?
To repair microdamages in the matrix.
What causes osteoporosis?
Imbalance between osteoclast-mediated bone resorption and osteoblast-mediated bone deposition. LACK OF ESTROGEN.
