Skeletal System

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Skeletal System
2015-09-24 23:16:23
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  1. Composition of the skeletal system
    • notochord
    • cartilage 
    • bone
  2. function of the skeletal system
    • form
    • locomotion
    • supports and protects viscera
    • stores Ca++ salts
  3. Explain the notochord: 

    extends from the tail up to the base of the skull just beneath the brain; does not extend forward
  4. Purpose of the notochord
    - in amphioxus and primitive
    In amphioxus and primitive: , it acts as the axial support of the body and it is extremely flexible in them so that when the fish start swimming, it straightens out—gives undulating movement
  5. Purpose of the notochord
    - in advanced fishes and tetrapods
    In advanced fishes and tetrapods: the vertebrae encroaches on the notochord; the vertebrae replace the notochord in its function as the chief axial support
  6. What does the notochord not contain?
    blood vessels or nerves
  7. Structure of the notochord
    a dorsal rod that is avascular and is not innervated (no nerves) made up of tightly packed cells with little or no intercellular space between the cells
  8. What do the cells of the notochord have?
    contain large vacuoles that are fluid-filled, which keep the cells turgent; and, with this, we have a stiffened rod
  9. What are the outside characteristics of the notochord?
    • Outer: elastic connective tissue to give some flexibility
    • Inner: thicker layer of dense fibrous CT
    • These sheaths are acellular; they are basically fibers; they play an important role in organisms tha tform vertebral columns
  10. Explain the inconstancy of the notochord.
    Only present as continuing structure in life of primitive fish; in other organisms, it is squeezed out by vertebrae or just barely exists in centrum of vertebrae
  11. General characteristics of cartilage
    : third to mammals the hardest tissue; provides form, structure, and support; found in both vertebrates and invertebrates; in condrichthians, it forms most or all of the skeleton; loss of bone in condrichthians may be adaptive thing; in all other vertebrates, it’s present to some extent alongside bone
  12. histology of cartilage
    avascular; gets its nutrient supply from a connective tissue covering that surrounds all cartilage called the perichondrium [chondrium=cartilage]; dense, fibrous, irregular tissue is the perichondrium
  13. What are the two cell types in cartilage?
    –chondroblasts and the chondrocytes; the former is the immature cartilage cell that is responsible for secreting the matrix of cartilage
  14. Explain the matrix in cartilage
    amorphous; embedded in it is the fibers and mucopolysaccharides; they get stuck in the matrix and become chondrocytes—not active in the matrix; mature; if you pull out the cell, the space that the chondrocyte resides in is called the lacuna
  15. What are the types of cartilage?
    • hyaline
    • fibrous
    • elastic
    • calcified
  16. hyaline cartilage
    –most prevalent cartilage in all vertebrates; the fibers in here are collagenous; pretty strong cartilage; it is the cartilage of many of the vertebrate skeletal structures before they are bone ; there are preformed cartilage models in the embryo of many structures; does not turn into bone; used as a template for bone to form
  17. fibrous cartilage
    –Fibrous: combination of dense fibrous CT and hyaline cartilage; chondrocytes line up between the dense bundles of fibers; very strong cartilage
  18. elastic cartilage
    –  Elastic: proteins are elastic; highly flexible; more stability; less support; the pinna of your ear is this
  19. calcified cartilage
    – Calcified: hyaline cartilage where there are bits of hydroxyapatite embedded in it; composed of calcium salts; the whole matrix is not embedded with it; but there are small bits of it; strongest of all the cartilages
  20. General characteristics of bone
    definitive bone is a uniquely vertebrate structure. However, what makes bone so hard is the hydroxyapatite, these calcium crystals found in both vertebrate and invertebrate organisms
  21. Explain the location of true bone
    True bone found in every vertebrate class except the chondrichthians; absence appears to be a secondary loss
  22. Explain bone in...

    bony fishes
    Most bony fishes: bone is composed of an acellular tissue; no osteocytes nor osteoclasts; largely matrix layered (lamellar bone)
  23. Explain bone in...

    amphibian, reptilian, and avian
    Amphibian, reptilian, and avian: largely lamellar (concentric layers of matrix); osteoblasts are present in two places-the periosteum [surrounds bone] and the endosteum [CT that lines spaces in the bone]
  24. Explain bone in...

    Mammalian: composed of osteoblasts periosteum and endosteum; osteocytes in lacunar spaces within the matrix and osteoclasts, which generally reside at the periphery of bone beneath the periosteum
  25. osteoblast
    immature bone cell; secretes matrix; and, like cartilage, there is a lot of matrix

    The cells reside in that matrix; two components of matrix—fibers (which are mostly collagenous) and the amorphous ground substance, which is some kind of mucopolysaccharide; active in mitosis and synthesis of the matrix; at some point, they mature and become osteocyte
  26. osteocyte
    mature cell that resides within a lacuna in the matrix; once hardened, the extensions are brought back in and what appears in the matrix are canals
  27. What makes bone different than cartilage?
    1) embedded in the matrix are: 1) blood vessels (bring with them hydroxyapatite (which is embedded throughout the matrix, not like the cartilage which has little spicules); and, this causes the matrix to harden.

    Once this hydroxyapatite occurs, there is no diffusion through the matrix, which is why the BV have to be present before that hydroxyapatite gets laid down
  28. osteoclasts
    Osteoclasts: gain cells not within bone but underneath periosteum; pretty inactive except in times of bone remodeling, bone injury, and bone growth; role not well understood; relatively inactive; play role in bone resorption (getting rid of the bone that needs to be remodeled, those pieces that need to e remodeled or repaired or making room for new bone)

    resides in the periphery of bone right underneath the periosteum
  29. Two kinds of bone
    dermal (membranous) bone

    replacement (endochondral) bone
  30. dermal (membranous) bone
    –bone forming in and upon a connective tissue membrane

    Ex: bones of the lower jaw—mandible; bones of the skull, pectoral girdle, other bone that develops in the integument, vertebrae in teleosts, urodyles, and apoda, and dentin
  31. replacement (endochondral) bone
    –Replacement (endochrondral) bone: bone forming in and upon a pre-cartilage model; most bones are formed endochondrally, not all however; all other bone not mentioned in dermal
  32. In mammalian bones, there are two histological orientations for bone. Explain the first.
    Most mammalian bones: random array of osteocytes embedded in matrix; not highly organized; may be lamellar or concentric; osteocytes located on line of concentric circle (imagine)
  33. In mammalian bones, there are two histological orientations for bone. Explain the second.
    There are some bones reorganized into Haversian systems—longitudinal array of bone; in the center of it is the Haversian canal; making up the wall of this system is osteocytes

    Haversian systems are only found in shafts of long bones of mammals; and its there that Haversian systems make up—in the diaphysis and what not; provides greatest amount of strength on bone
  34. Explain the epiphyseal plate
    In epiphyseal plate, the cartilage gets bigger and some gets destroyed as it breaks down
  35. Matrix components
    –Inorganic components- 60% is inorganic hydroxyapatite (the calcium salts), which also provide strength, but compressive type of stress
  36. organic components in bone matrix
    fibers such as collagen
  37. Forms of bone?
    • compact (dense)
    • cancellous (spongy)
  38. compact/ dense bone
    all solid bone; it can have a canal running through it and canaliculi, but it does not have the honeycomb appearance much stronger bone, which is why it is used to protect spongy bone; osteocytes and matrix
  39. cancellous/ spongy bone
    Cancellous (spongy) bone: spicules or spears of bone and several clear spaces, which can be filled with yellow marrow (fat) or red marrow (hemopoietic tissueà gives rise to red blood cells); wherever you have spongy bone, it is covered by a thick layer of compact bone because it can easily be broken
  40. True or False: 

    All bone that is made is spongy and then gets remodeled to become compact.
  41. In terms of classifying bones, what are the categories?
    • long
    • short 
    • flat
    • irregular
  42. Long
    -length is greater than their width; they have two ends—epiphyses –and the center is the diaphysis, which is all compact bone, which is where you have your Haversian systems; center of diaphysis is hollow because if it were too heavy, it’d be solid bone; epiphyes are spongy bone covered with a thin layer of compact bone;
  43. In some long bones, what is up?
    -In some long bones, there is a cartilage plate called the epiphyseal plate; it is hyaline cartilage and it allows for the lengthening of long bones; at the end of the growth period, that cartilage becomes bone
  44. Short bones
    bones that have a similar/ equal length and width; they are spongy bone covered with a thin layer of compact; carpals are examples
  45. flat bones
    -really compact on the outside, compact on the inside, and a thin layer of spongy in the middle (flat bones of skull are examples)
  46. irregular bones
    bones that don’t fit into the other categories (ex: patella); mainly spongy covered by a thin layer of compact
  47. Haversian system
    A longitudianl array of bone found in long bones of many mammals