Bone Histology, Matrix Composition, and Clinical Pathologies

A set of comprehensive question-and-answer flashcards covering bone cells, extracellular matrix composition, Osteitis deformans, and bone formation and resorption mechanisms.

What are osteoprogenitor cells and where in bone tissue are they located?

Osteoprogenitor cells are bone stem cells derived from mesenchyme that are located in both the periosteum and the endosteum.

What two cells are produced when an osteoprogenitor cell undergoes cellular division?

Cellular division of an osteoprogenitor cell produces another stem cell along with a "committed cell" that matures to become an osteoblast.

What shape and organelles characterize active osteoblasts, and what matrix component do they secrete?

Active osteoblasts exhibit a cuboidal shape, contain abundant rough endoplasmic reticulum and Golgi apparatus, and secrete osteoid.

How do osteoblasts transition into osteocytes?

Osteoblasts differentiate into osteocytes once they become entrapped within the bone matrix they produce and secrete.

What are the primary functions of osteocytes within bone tissue?

Osteocytes maintain the bone matrix and detect mechanical stress, signaling osteoblasts to deposit new bone matrix at the surface when stress is detected.

What is the specific depression or pit on the bone surface where an osteoclast is often located?

A resorption lacuna (Howship's lacuna).

What structural feature on osteoclasts increases their surface area exposure to bone?

A ruffled border where the osteoclasts contact the bone.

What causes Osteitis deformans (Paget disease of bone)?

Osteitis deformans results from a disruption in the balance between osteoclast and osteoblast functions, characterized by excessive bone resorption followed by excessive bone deposition.

How do osteoclasts in Osteitis deformans differ in size and nuclear count from healthy osteoclasts?

Osteoclasts in Osteitis deformans are five times larger than normal and may contain 20 or more nuclei, compared to about 3 to 5 nuclei in healthy osteoclasts.

Which bones are most commonly affected by Osteitis deformans?

The skull, hip bones, vertebrae, femur, and tibia.

According to Learning Strategy 7.2, what represents the concrete and rebar in bone matrix, and what happens if either is missing?

Collagen fibers represent rebar and hydroxyapatite represents concrete; without hydroxyapatite (concrete) the rebar bends, and without collagen (rebar) the concrete crumbles.

What are the organic components of the extracellular matrix of bone and what functional property do they provide?

The organic component is osteoid, composed of collagen proteins and ground substance (proteoglycans like chondroitin sulfate, and glycoproteins); it gives bone tensile strength and flexibility.

What inorganic chemical crystals form hydroxyapatite in bone matrix, and what functional property do they confer?

Hydroxyapatite, $Ca_{10}(PO_4)_6(OH)_2$, is formed by the interaction of calcium phosphate, $Ca_3(PO_4)_2$, and calcium hydroxide, $Ca(OH)_2$; it hardens the matrix to provide rigidity and compressional strength.

What structural changes occur in bone matrix from a loss of protein versus an insufficiency of calcium?

A loss of protein or the presence of abnormal protein results in brittle bones, whereas insufficient calcium results in soft bones.

What specific roles do Vitamin D and Vitamin C play in bone matrix formation?

Vitamin D enhances calcium absorption from the gastrointestinal tract, and Vitamin C is required for collagen formation.

Which specific substances stored in osteoclast lysosomes perform bone resorption, and what are their functions?

Proteolytic enzymes digest organic components (collagen fibers, proteoglycans, and glycoproteins), and hydrochloric acid ($HCl$) dissolves inorganic mineral parts (calcium and phosphate crystals).

What is osteolysis and when does bone resorption occur?

Osteolysis is the release of stored calcium and phosphate from the bone matrix into extracellular fluid and blood; bone resorption occurs during bone remodeling and when blood calcium levels are low.