5.1 Structure And Function Of Bone

• What type of tissue is bone classified as?

  Bone is classified as a specialized form of connective tissue.
• What are the main components of connective tissues, including bone?

  Connective tissues are composed of specialized cells, protein fibers, and an extracellular matrix.
• What is another name for bone tissue?

  Bone tissue is also known as osseous tissue.
• What gives bone tissue its solid and sturdy characteristics?

  The deposition of calcium salts around the protein fibers gives bone tissue its solid and sturdy characteristics.
• What separates osseous tissue from surrounding tissues?

  Osseous tissue is separated from surrounding tissues by a fibrous periosteum.
• What lines the inner bony surfaces when osseous tissue surrounds another tissue?

  The inner bony surfaces are lined by a cellular endosteum.
• What accounts for almost two-thirds of the weight of bone?

  Calcium phosphate, $Ca_3(PO_4)_2$, accounts for almost two-thirds of the weight of bone.
• What do calcium phosphate and calcium hydroxide form when they interact?

  Calcium phosphate and calcium hydroxide interact to form crystals of hydroxyapatite.
• What role do the inorganic components of bone play?

  The inorganic components enable bone to resist compression.
• What provides bone with considerable tensile strength?

  Collagen fibers and other noncollagenous proteins provide bone with considerable tensile strength.
• How do calcium phosphate crystals behave under stress?

  Calcium phosphate crystals withstand compression but shatter when exposed to bending, twisting, or sudden impacts.
• What is the function of collagen fibers in bone?

  Collagen fibers tolerate stretching, twisting, and bending but bend out of the way when compressed.
• What do osteocytes do in bone tissue?

  Osteocytes maintain and monitor the protein and mineral content of the surrounding matrix.
• What are the small chambers occupied by osteocytes called?

  Osteocytes occupy small chambers called lacunae.
• What are the channels that connect lacunae called?

  The channels that connect lacunae are called canaliculi.
• What is the role of tight junctions between osteocyte processes?

  Tight junctions interconnect osteocyte processes and provide a route for the diffusion of nutrients and waste products.
• What are osteoblasts?

  Osteoblasts are cuboidal cells that secrete the organic components of the bone matrix.
• What is osteoid?

  Osteoid is the organic material secreted by osteoblasts that later becomes mineralized.
• What initiates osteogenesis?

  Osteoblasts respond to various stimuli, including mechanical and hormonal, to initiate osteogenesis.
• What are osteoprogenitor cells?

  Osteoprogenitor cells are small numbers of stem cells found in bone tissue.
• Where are osteoprogenitor cells found?

  Osteoprogenitor cells are found in the innermost layer of the periosteum and the endosteum lining the medullary cavities.
• What happens to osteoprogenitor cells after they divide?

  After dividing, osteoprogenitor cells differentiate into osteoblasts.
• Why is the ability to produce additional osteoblasts important?

  The ability to produce additional osteoblasts is important after a bone is cracked or broken.
• What are osteoclasts?

  Osteoclasts are large, multinucleate cells found at sites where bone is being removed.
• What process do osteoclasts perform to dissolve the bony matrix?

  Osteoclasts secrete acids through a process involving the exocytosis of lysosomes to dissolve the bony matrix.
• What is osteolysis?

  Osteolysis is the erosion process that increases calcium and phosphate concentrations in body fluids.
• What is the balance between the activities of osteoblasts and osteoclasts important for?

  The balance between the activities of osteoblasts and osteoclasts is important for maintaining bone strength.
• What happens when osteoclasts remove calcium salts faster than osteoblasts deposit them?

  When osteoclasts remove calcium salts faster than osteoblasts deposit them, bones become weaker.
• What happens when osteoblasts are more active than osteoclasts?

  When osteoblasts are more active than osteoclasts, bones become stronger and more massive.
• What are the two forms of adult bone?

  • Compact bone
  • Spongy bone
• How does compact bone differ from spongy bone in terms of structure and function?

  Compact bone is heavier and better at resisting forces that occur parallel to the bone, while spongy bone is lighter and better at resisting forces from multiple directions.
• What is the term for spongy bone?

  Spongy bone is also termed trabecular bone or cancellous bone.
• Where is compact bone typically found in the skeleton?

  Compact bone forms the walls, and an internal layer of spongy bone surrounds the medullary cavity in typical bones of the skeleton.
• What does the medullary cavity contain?

  The medullary cavity contains bone marrow.
• What are the two types of bone marrow found in the medullary cavity?

  The two types of bone marrow are yellow marrow and red marrow.
• What is the function of yellow marrow?

  Yellow marrow serves as an important energy reserve.
• What is the function of red marrow?

  Red marrow is an important site of blood cell formation.
• What are the structural differences between compact and spongy bone?

  • Compact bone is dense and solid.
  • Spongy bone forms an open network of struts and plates.
  • Both have the same matrix composition but differ in the arrangement of osteocytes, canaliculi, and lamellae.
• What is the functional unit of mature compact bone?

  The functional unit of mature compact bone is the cylindrical osteon, or Haversian system.
• How are osteocytes arranged in an osteon?

  In an osteon, osteocytes are arranged in circular layers around a central canal.