Histo Lecture 10 II

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Histo Lecture 10 II
2010-10-21 15:00:57

Bones II Lecture
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  1. Intramembranous Ossification is responsible for formation of for:
    • Bone healing
    • Growth of flat bones (i.e. skulls, carpals, tarsals)
    • Thickening of long bones
  2. What are the steps of osteoblasts in intramembranous ossification?
    • Osteoblasts secrete organic matrix (osteoid)
    • Osteoblasts then directly mineralize the matrix with hydroxyapatite crystals
    • Once surrounded by calcified matrix, osteoblasts become osteocytes
  3. Osteoblasts are formed by differentiation of cells of the:
    Periosteum and endosteum or bone marrow stem cells (mesenchyme)
  4. What function do chondrocytes perform?
    Produce cartilage and calcify the matrix
  5. Where do osteoblasts deposit bone matrix (osteoid)?
    Over the pre-existing cartilage matrix
  6. Function of osteoblasts/osteocytes
    Remove remnants of cartilage matrix resulting in typical bone matrix
  7. Endochostral ossification is responsible for
    • Growth of long bones
    • Bone healing
  8. Area of normal hyaline cartilage and chondrocytes
    Resting zone
  9. Area of intestine mitosis (proliferation) of chondrocytes
    Proliferative zone
  10. What happens in the Hypertrophic Zone?
    • Area of chondrocyte hypertrophy due to glycogen uptake
    • Cartilage ECM is partially resorbed
    • Remnants appear as septa of matrix material between hypertrophic chondrocytes
  11. What happens in the Calcified cartilage zone?
    • Thin septa of cartilage matrix become calicified
    • Chondrocytes in this zone die after matrix calcification
  12. The Ossification zone is in charge of being
    • The osteoprogenitor cells from the bone marrow are delivered to the calcified cartilage
    • -Osteoprogenitor cells differentiate into osteoblasts
  13. Osteoblasts deposit bone matrix over calcified cartilage matrix
  14. Following ossification, the _____ cartilage is resorbed, leaving a calcified bone matrix, which is ______ bone tissue
    old; "true"
  15. Overall, the thickness of the _________ _______ does not change as that rate of bone production and cartilage growth are equal at opposite ends.
    Epiphyseal plate
  16. Endochondral ossification during fetal development is a ______ process
  17. Bone under goes ________ remodeling througout life.
  18. Bone remodeling is dependent on ________ placed on bones
    stresses (forces)
  19. Stresses placed on bones affect:
    Deposition and resorption
  20. State Wolff's Law
    Every change in form and function of bone, or in its function alone, is followed by certain, definite changes in its internal architecture and external form.
  21. Describe the process of how bones are repaired from a fracture
    • Damaged blood vessels produce a localized clot
    • Clot material is later removed by macrophages
    • Periosteum and Endosteum repond with intense proliferation of cells
    • Periosteal/endosteal fibroblasts differentiate into chondroblasts and hyaline cartilage model = soft callus
    • Mesenchyme cells differentiate into osteoblasts and form osteoid
    • Endochondral and intramembranous ossification occur to form primary (woven) bone = hard callus
    • Hard callus is replaced by lamellar bone
  22. Healing Time Table
    • Soft callous - 2 wks
    • Hard callous - 4 wks
    • Lamellar bone - 6 wks
  23. Does stress affect healing bone?
    Yes. Healing bone is influenced by stresses placed upon it during the healing process
  24. How does inactivity affect bones?
    • Inactivity or decreased loading of bone results in reduced osteoblast activity but does not affect osteoclast activity
    • Overall result is increased degradation of bone and increase in serum CA++ levels
  25. What 3 qualities of bone change with increased loading?
    • Hypertrophy of bone
    • ↑ bone mass/density
    • ↑ load to failure (strength)
  26. Repetitive loading on bone creates:
    microscopic deformities
  27. What aides the bone healing process?
  28. What causes stress fratures?
    Stress fractures result when loading outpaces bone repair/remodeling
  29. What is Osteopenia?
    • Reuction in bone mineral density below normal levels, results in decreased bone strength
    • (Often a precursor to the development of osteoporosis)
  30. What causes Osteopenia?
    Inactivity, aging, low intake of vitamin D and calcium, and smoking
  31. What is the definition of Osteoporosis?
    Defined as decrease in bone density and decrease in overall volume of bone
  32. How is Osteopenia classified?
    1 to 2.5 standard deviations from the norm
  33. How is Osteoporosis classified?
    Greater than 2.5 standard deviations from normal BMD
  34. How many Americans have osteoporsis?
    10 million (80% females)
  35. Name some risk factors for Osteoporosis
    • Female
    • Older age
    • Small frame
    • Caucasian, Asian, Hispanic
    • Menopause
    • Inactivity
    • Poor diet (Low Vit D % calc; excess protein, sodium, caffeine)
    • Smoking, alcohol abuse
    • Steroid medications
    • Anorexia, RA, GI pathology
  36. What percent of the body's calcium is stored in bone?
  37. Calcium levels are controlled by what system?
    endocrine system
  38. What are 3 regulators in calcium metabolism?
    • -Parathyroid hormone
    • -Calcitonin
    • -Vitamin D
  39. How is Hypercalcemia determined?
    • >10.5 mg/dL of blood
    • Causes mild to severe proximal weakness in extremities
  40. How is Hypocalcemia determined?
    • <8.5 mg/dL of blood
    • neurmosucular excitability and muscular tetany (especially UE flexion)
  41. What is secreted in response to low levels of Ca++ in the plasma?
    Parathyroid Hormone
  42. PTH promotes what action in the bone?
    Osteoclast resorption and liberation of Ca++ into the blood
  43. Where does PTH bind?
    • Osteoblasts
    • -Osteoblasts stop producing bone
    • -Osteoblasts secrete an osteoclast-stimulating factor
  44. Where else does PTH act to affect calcium levels?
    • Enhances calcium absorption from intestines
    • Decreasese calcium excretion by kidneys
  45. The thyroid gland synthesizes what hormone in response to elevated levels of Ca++ in the blood?
  46. What is the function of Calcitonin?
    • Inhibits matrix resorption by osteoclasts
    • Inhibits new osteoclast formation
  47. What vital bone cell does Calcitonin NOT interact with?
  48. What is essential for intestinal absorption of Ca++ and PO4- from the kidney?
    Vitamin D
  49. Vitamin D is necessary for active reabsorption of Ca++ and PO4- from what organ?
    The kidney
  50. What stimulates the formation of Vitamin D?
    UV light
  51. What processes inative Vitamin D? What activates it?
    liver; kidneys
  52. 4 characteristics of Diarthrodial Joint
    • Capsule
    • Outer fibrous layer
    • Inner synovial layer (synovial membrane)
    • Joint cavity
  53. Define synovial fluid
    Viscous, colorless & transparent fluid formed from a dialysate of plasma
  54. The outer fibrous layer is comprised of what 3 things
    • Dense irregular CT
    • Continuation of periosteum
    • Continuation with tendons and ligaments
  55. Functions of Joint Capsule
    • Nourishment (Direct vascular supply)
    • Innervation (Mechanoreceptors, Free nerve endings, GVA/GVE to vasculature)
  56. Cell types of synovium
    • F cells - Synthesize large amounts of hyaluronic acid that is secreted into the synovial fluid
    • M cells - Differentiated blood monocyte that serves as phagocytic cell of synovial membrane
  57. Functions of the synovium
    • Nourishment
    • -Highly vascularized
    • -No neural innervation
    • Produces synovial fluid for waste/nutrient exchange
    • Synovial fluid to improve frictionless motion
  58. Main constituents on Synovial Fluid
    • Hyaluronic acid
    • Water
    • Electrolyte composition similar to plasma
  59. Function of Synovial Fluid
    • Delivers O2 to articular cartilage
    • Medium for removal of waste products
    • Reduces friction on articular surfaces
  60. What are syndesmosis?
    • When bones are united by dense connective tissue
    • -ex. interosseus ligament between radius and ulna
  61. What are Synchondrosis?
    • Bones are united by hyaline cartilage
    • -ex. epiphyseal plates, sternocostal joints
  62. What is Symphysis?
    • Bones united by fibrocartilage. Type of Synchondrosis
    • -ex. pubic symphysis and IV disks
  63. What are syntosis?
    • Bones are united by bony tissue that has replaced normal synarthroses
    • -Ex. cranial sutures in adults, epiphyseal plates upon maturity