Ch. 6 Bones and Skeletal Tissues

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  1. Articular Cartilage
    Composed of?
    Surrounded by?
    • covers the ends of most bones at movable joints
    • is composed of the connective tissue cartilage, which contains no nerves or blood vessels
    • the structure is surrounded by a layer of dense irregular connective tissue, the perichondrium
  2. Perichondrium
    • which acts like a girdle to resist outward expansion when the cartilage is subjected to pressure
    • also functions in the growth and repair of cartilage
  3. Three types of Cartilage tissue occur in the body:
    • Hyaline Cartilage
    • Elastic Cartilage
    • Fibrocartilage
  4. Cartilage (Fig. 6.2)
    Matrix contains?
    • is a connective tissue that consists of cells called chondrocytes and an abundant extracellular matrix
    • each chondrocyte is located in a space in the matrix called a lacuna (a "lake" or "cavity")
    • the matrix contains fibers and a jellylike ground substance of complex sugar molecules that attract and hold water
    • consists primarily of water (60% to 80%) and is very resilient; that is, it has the ability to spring back to its original shape after being compressed
  5. Hyaline Cartilage ("glass")
    • which looks like frosted glass when viewed by the unaided eye, is the most abundant kind of cartilage
    • when viewed under the LM, its chondrocytes appear spherical
    • the only type of fiber in the matrix is a collagen unit fibril, which forms networks that are too thin to be seen with a LM
    • the gelatinous ground substance holds large amounts of water; thus, this tissue resists compression well
    • provides support through flexibility and resilence
  6. Elastic Cartilage
    • is similar to hyaline cartilage, but its matrix contains many elastic fibers along with the delicate collagen fibers
    • it is better able to tolerate repeated bending
  7. Fibrocartilage
    Two specific locations of fibrocartilage?
    • is an unusual tissue that resists both strong compression and strong tension (pulling) forces
    • it consists of thick collagen fibers (as in dense regular connective tissue) surrounding the chondrocytes within lacunae
    • are in the anulus fibrosus portion of the disc between the vertebrae and in the articular discs of some joints, for example the menisci of the knee
  8. Cartilaginous structures grows in two?
    • Appositional growth, "growth from outside," cartilage forming cells (chondroblasts) in the surrounding perichondrium produce the new cartilage tissue by actively secreting matrix
    • Interstitial growth, "growth from within," the chondrocytes within the cartilage divide and secrete new matrix
  9. Cartilage grow rapidly during?
    Cartilage stops growing?
    As a result?
    • the embryonic development, childhood, and adolescence 
    • in the late teens, when the skeleton itself stops growing, and chondrocytes do not divide again
    • cartilage regenerates poorly in adults
  10. Function of Bones: Pg. 127
    • Support
    • Movement
    • Protection
    • Mineral storage
    • Blood cell formation and energy storage
    • Energy Metabolism
  11. Extracellular Matrix of bone
    Organic components?
    Inorganic components?
    • it is the unique composition of the matrix that gives bone its exceptional physical properties
    • the organic components of bone account for 35% of the tissue mass→particularly collagen fibers, contribute the flexibility and tensile strength that allow bones to resist stretching and twisting
    • 65% by mass, consists of inorganic hydroxyapaptities, or mineral salts, primarily calcium phosphate→these mineral salts are present as tiny crystals that lie in and around the collagen fibrils in the extracellular matrix →the crystals pack tightly, providing bone with its exceptional hardness, which enables it to resist compression
  12. Three types of cells in bone tissue produce or maintain the tissue:
    Fourth type of cell found within bone tissue?
    • Osteogenic cells (osteo=bone, genice=producing) are stem cells the differentiate into bone-forming
    • ↳ Osteoblasts (blast=bud, sprout) are cells that actively produce and secrete the organic components of the bone matrix
    • ↳ the bone matrix secreted by osteoblasts is called osteiod ("bonelike") within a week, inorganic calcium salts crystallize within the osteiod 
    • Once osteoblasts are completely surrounded by bone matrix and are no longer producing new osteiod, they are called
    •  Osteocytes (cytes=cell) function to keep the bone matrix healthy
    • → if osteocytes die or are destroyed, the bone matrix is resorbed by Osteoclasts (clast=break) are derived from a linage of white blood cells; these multinucleated cells break down bone by secreting hydrochloric acid, which dissolves the mineral component of the matrix, and lysosomal enzymes, which digest the organic components
  13. Structure of a Typical Long Bone (Fig. 6.4)
    • Diaphysis or shaft, forms the long axis of a long bone
    • Epiphyses are the bones ends
    • ↳ the joint surface of each epiphysis is covered with a thin layer of hyaline cartilage called the articular cartilage 
    • Between the diaphysis and each epiphysis  of an adult long bone is an epiphyseal line→this line is a remnant of the epiphyseal plate, commonly called the growth plate, a disc of hyaline cartilage that grows during childhood to lengthen the bone
  14. Structure of a Typical Long Bone: Blood Vessels (Fig. 6.4c)
    • unlike cartilage, bones are well vascularized
    • in fact, at any given time between 3% and 11% of the blood in the body is in the skeleton 
    • The main vessels serving the diaphysis are a nutrient artery and a nutrient vein→together these run through a hole in the wall of the diaphysis, the nutrient foramen ("opening")→the nutrient artery runs inward to supply the bone marrow and the spongy bone→branches then extend outward to supply the compact bone
  15. Structures of a Typical Long Bone: The Medullary Cavity ("middle")
    • the very center of the diaphysis of long bones contains no bone tissue at all
    • also called the marrow cavity→as the name implies, in adults this cavity is filled with yellow bone marrow
  16. Periosteum ("around the bone")
    The periosteal membrane has two sublayers:
    • a connective tissue membrane, covers the entire outer surface of each bone except the ends of the epiphyses, where articular cartilage occurs
    • a superficial layer of dense irregular connective tissue, which resists tension placed on a bone during bending, and a deep layer that abuts the compact bone
    • the deeper layer is osteogenic, containing bone-depositing cells (osteoblasts) and bone-destroying cells (osteoclasts)
    • ↳these cells remodel bone surfaces throughout our lives→during periods of bone growth or deposition, the osteogenic cells differentiate into osteoblasts→these osteoblasts produce the layers of bone tissue that encircle the perimeter of the bone, the circumferential lamellae
    • the periosteum is richly supplied with nerves and blood vessels
    • the periosteum is secured to the underlying bone by perforating collagen fibers (Sharpey's fibers), thick bundles of collagen that run from the periosteum into the bone matrix
    • the periosteum also provides insertion points for the tendons and ligaments that  attach to a bone→at these points, the perforating collagen fiber bundles are exceptionally dense
  17. Endosteum
    • a thinner connective tissue membrane that covers the internal bone surfaces
    • specifically, endosteum covers the trabeculae of spongy bone; it also lines the central canals of osteons
  18. Structure of Short, Irregular, and Flat Bones
    • they all have much the same composition as long bones: periosteum-covered compact bone externally and endosteum-covered spongy bone internally
    • they have no diaphysis and no epiphysises; they contain bone marrow (between the trabeculate of their spongy bone), but no marrow cavity is present
    • In flat bones, the internal spongy bone is called diploe
  19. Bone markings fit into three categories: Pg.133
    • (1) Projections that are the attachment sites for muscles and ligaments
    • (2) Surfaces that form joints
    • (3) Depressions and openings
  20. Compact Bone
    • to the unaided eye, compact bone looks solid
    • however, microscopic examination reveals that it is riddled with passageways for blood vessels and nerves
    • Osteon or Harversian system
  21. Connection
    • Hyaline Cartilage makes up the articular cartilage that covers the ends of adjoining bones in movable joints
    • The epiglottis, which bends down to cover the glottis (opening) of the larynx each time we swallow, is made of elastic cartilage
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Ch. 6 Bones and Skeletal Tissues
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