skeletal tortora

• Bone tissue is a complex and dynamic living tissue
• Bone remodeling


  1. Building of new bone tissue

  2. Breaking down of old bone tissue
• Young, healthy men in prime physical shape returned from their space flights only to alarm their physicians
• Physical examinations of the astronauts revealed that they had lost up to 20% of their total bone density during their extended stay in space
• Zero-gravity (weightless) environment of space


  Placed minimal strain on the astronauts' bones
• Athletes


  Subject their bones to great forces, which place significant strain on the bone tissue
• Accomplished athletes show an increase in overall bone density
• Bone


  Capable of changing in response to the different mechanical demands placed on it
• High activity levels that strain bone tissue greatly improve bone health
• Bone tissue


  Continuously growing, remodeling, and repairing itself
• Bone tissue


  • Contributes to homeostasis of the body by providing support and protection, producing blood cells, and storing minerals and triglycerides
• Bone tissue contains red bone marrow
• Diaphysis


  The bone's shaft or body—the long, cylindrical, main portion of the bone

  
• Epiphyses


  The proximal and distal ends of the bone

  
• Metaphyses


  The regions between the diaphysis and the epiphyses
• Epiphyseal (growth) plate


  A layer of hyaline cartilage that allows the diaphysis of the bone to grow in length

  
• Epiphyseal line


  The bony structure that results when the cartilage in the epiphyseal plate is replaced by bone

  
• Articular cartilage


  A thin layer of hyaline cartilage covering the part of the epiphysis where the bone forms an articulation (joint) with another bone

  
• Periosteum


  A tough connective tissue sheath and its associated blood supply that surrounds the bone surface wherever it is not covered by articular cartilage

  
• Medullary cavity


  A hollow, cylindrical space within the diaphysis that contains fatty yellow bone marrow and numerous blood vessels in adults
• Endosteum


  A thin membrane that lines the medullary cavity
• Extracellular matrix of bone tissue

  About 15% water, 30% collagen fibers, and 55% crystallized mineral salts

  
• Hydroxyapatite


  Crystals formed by the combination of calcium phosphate, calcium hydroxide, and other mineral salts
• Calcification


  The process of mineral salts crystallizing in the framework formed by the collagen fibers of the extracellular matrix
• Types of cells in bone tissue

  • Osteoprogenitor cells
  • Osteoblasts
  • Osteocytes
  • Osteoclasts
• Osteoprogenitor cells


  Unspecialized bone stem cells derived from mesenchyme, the tissue from which almost all connective tissues are formed

  
• Osteoblasts


  Bone-building cells that synthesize and secrete collagen fibers and other organic components needed to build the extracellular matrix of bone tissue, and initiate calcification

  
• Osteocytes


  Mature bone cells that maintain the daily metabolism of bone tissue
• Osteoclasts


  Huge cells derived from the fusion of monocytes (a type of white blood cell) that function in the breakdown of bone extracellular matrix (bone resorption)
• Issue cell


  The cell maintains and monitors the tissue
• Osteoclasts


  • Huge cells derived from the fusion of as many as 50 monocytes (a type of white blood cell) and are concentrated in the endosteum
  • On the side of the cell that faces the bone surface, the osteoclast's plasma membrane is deeply folded into a ruffled border
  • Here the cell releases powerful lysosomal enzymes and acids that digest the protein and mineral components of the underlying extracellular bone matrix
  • This breakdown of bone extracellular matrix, termed bone resorption, is part of the normal development, maintenance, and repair of bone

  
• • clast


  Means the cell breaks down extracellular matrix
• Osteoclasts help regulate blood calcium level in response to certain hormones
• Osteoclasts are target cells for drug therapy used to treat osteoporosis
• Mnemonic


  Memory device to learn new or unfamiliar information
• Osteooblasts build bone, while osteoClasts carve out bone

  
• Bone is not completely solid but has many small spaces between its cells and extracellular matrix components

  
• Some spaces serve as channels for blood vessels that supply bone cells with nutrients
• Other spaces act as storage areas for red bone marrow
• Compact bone


  Contains few spaces and is the strongest form of bone tissue