Skeletal system: Bone tissue 2

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Skeletal system: Bone tissue 2
2012-06-27 18:04:42
Skeletal system Bone tissue

Skeletal system: Bone tissue 2
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  1. Blood and Nerve supply of Bone: Nutrient Artery
    Near the centre of the Diaphysis it passes through a hole in the compact bone called the Nutrient Foramen
  2. Blood and Nerve supply to Bones: Nutrient Veins
    veins that carry blood away from long bones.  This one accompanies the Nutrient Artery.
  3. Bone Formation: Ossification
    when mesenchmal cells become transformed into osteogenic cells.  These undergo cell division and give rise to cells that differentiate into osteoblasts, osteoclasts, and osteocytes

    • -begins during the sixth week of embryonic life.  
    • -The two types of ossification are Intramembranous and endochondral. Both result in replacing preexisting connective tissue with bone 
  4. Ossification: Intramembranous
    • refers to the bone formation directly within the mesenchyme arranged in sheetlike layers that resemble membranes
    • Steps:
    • 1. Development of the ossification centre: chemical messages cause the mesenchymal cells to cluster together and differentiate, first into osteogenic cells and then into osteoblasts.
    • 2. Calcification: Next, the secretion of extracellular matrix stops and the cells, now called osteocytes, lie in the lacunae and extend their narrow cytoplasmic processes into canaliculi.  Within a few days calcium and other minerals are deposited and the extracellular matrix hardens
    • 3. Developement of the periosteum:  
  5. Endochondral ossification
    • The replacement of cartillage by bone
    • Steps:
    • 1. Development of the cartillage model: chemical signals tell the mesenchymal to crowd in the shape of the future bone and then to develope into chondroblasts.  These secret extracellular material making the cartillage model consisting of hyaline cartillage.  A covering called the perichondrium develops around the cartilage model. 
    • 2. Growth of Cartilage model: cell division of chondrocytes causes the cartilage model to grow.  As the cartilage model continues to grow chondrocytes in its midregion increase in size causing the surrounding chondrocytes and extra cellular matrix to calcify.  This causes other chondrocytes to die becuase nutrients can no longer diffuse quickly enough.  As these chondrocytes die lacunae are formed and eventually merge into small cavities.
    • 3. Development of the primary ossification: A nutrient artery penetrates the perichondrium and the calcifying cartilage model, stimulating cells in the perichondrium to differentiate into osteoblasts instead of chondroblasts. Osteoblasts then begin to deposit bone extracellular material over the calcified cartilage matrix, forming spongy bone trabeculae.
    • 4. Development of the medullary: as the primary ossiffication centre grows towards the ends of the bone, osteoclasts breakdown some of the newly formed spongy bone trabeculae.  This activity leaves a cavity. The medullary cavity
    • 5. Development of the secondary ossification centre: When branches of the epiphyseal artery enter the epiphysis the secondary ossification centre develops
    • 6. Formation of articualry cartilage and the epiphyseal plate: 
  6. Epiphyseal growth plate
    consists of four zones:  Zones of resting cartilage, Zone of proliferating cartillage, Zone of hypertrophic cartilage and zone of calcified cartilage

    -Because of cell division in the epiphyseal growth plate the diaphysis of a bone increases in length 
  7. Bone Thickness
    Bone thickness grows in diameter due to the addition of new bone tissue by periosteal osteoblasts around the outer surface of the bone(appositional growth)
  8. Bone remodeling
    is an ongoing process in which osteoclast carve out small tunnels in old bone tissue and the osteoblasts rebuild it.
  9. Bone Resorption
    osteoclasts release enzymes and acids that degrade collagen fibers and dissolve mineral salts in bone resorption
  10. Bone deposition
    the addition of minerals and collagen fibers to bone by osteoblasts
  11. Repairing fractures
    • 1. Formation of Fracture hematoma: As blood leaks from the torn ends of the vessels a mass of blood forms around the site of the fracture.  This mass of blood is called a Fracture Hematoma
    • 2. Fibrocartilaginous callus formation: fibroblasts from the periosteum invade the fracture site and produce collagen fibres. In addition cells from the periosteum develop into chondroblasts and begin to produce fibrocartilage in this region. These events lead to the creation of a fibrocartilaginous callus
    • 3. Bony callus formation: osteogenic cells develop into osteoblasts, which begin to produce spongy bone trabeculae.  These join the living and dead portions of the original bone fragments.  
    • 4. Bone remodeling: Dead portions of the original fragments of borken bone are gradually reabsorbed by osteoclasts.  Compact bone replaces spongy bone around the periphery of the fracture 
  12. Bone's role in calcium homeostasis
    bone is the major reservoir for calcium in the body.  Helps maintain calcium levels in the body through different processes
  13. Parathyroid hormone
    • secreted by parathyroid glands
    • -this hormone increases clood Ca2+ levels.  A PTH secretion operates through a negative feedback system. If something causes the calcium level to drop Paraythoid gland cells detect this change and start making more AMP which tells the cell to start synthesizing more PTH and sending it out into the blood.  This increases the number of active osteoclasts. which step up the pace of bone resorption. 
  14. Calcitriol
    a hormone that promotes absorption of calcium from foods in the gastriointestinal tract into the blood.
  15. calcitonin
    inhibits activity of osteoclasts, speeds calcium uptake by bone and speeds up calcium depostion into bone
  16. osteoarthritis
    the degeneration of articular cartilage such that the bony ends touch
  17. osteomyelitis
    an infection of bone characterized by high fever, sweating, chills, pain, nausea.  It is often caused by bacteria