Bone Formation, Role in Homeostasis and Repair


Describe bone formation in the fetus and the process of bone remodeling:

  1. Fetal skeleton is primarily composed of ____________ ________ and fibrous CT
  2. This  cartilage “model” is covered with bone matrix by ___________ (secrete ______)  and the cartilage is digested (begins 6th/7th week)
  3. Two methods of bone formation involve replacing CT with bone

____________________________ : bone form on/in fibrous CT

a.      simpler method: used for flat bones of skull and mandible and sealing sutures after birth 

b.      mesenchymal cells (tissue all CT comes from ) differentiate into osteogenic cells that beomce osteoblasts secreting matrix

c.      once trapped in their lacunae the osteocytes extend pm into canaliculi; salts are deposited and matrix hardens

d.      formation of trabeculae: as matrix forms it becomes trabeculae that fuse to form spongy bone; blood vessels grow in between trabeculae spaces and mesenchyme along newly formed bone; CT with blood vessels becomes red bone marrow

e.      development of periosteum: peripheral mesenchyme becomes periosteum, surface layersof spongy bone become compact bone

f.      much of the nre bone is reshaped into its adult size


_________________________ : form bone within hyaline cartilage

g.      most bones made this way

h.      development of the cartilage model: bone site: mesenchymal cells form the shape of the future bone and develop into chondroblasts secreting cartilage matrix making a hyaline model.

  1. Long bone growth at epiphyseal plate is controlled by GH


Bone Remodeling in life is due to

  1. Ca+ in the blood
    1. Ca+ low: parathyroid glands release _______ which activates ____________which destroy bone releasing Ca+ back into the bloodstream
    2. Ca+ high (____________________) Ca should be deposited into bone
  2. pull of gravity and muscles
    1. muscles attach to “bulky” bone and osteoblasts lay down new matrix and get trapped = osteocytes
    2. ie. Gymnasts, equestrians
    3. physical therapy


Types of Bone Fractures:

  1. Simple
  2. Closed and open (compound) fractures
  3. Greenstick
  4. Spiral
  5. comminuted
  6. compression
  7. depressed
  8. impacted


Bone Repair:

  1. Hematoma forms
  2. ______________ callus : grow new capillaries into clotted blood= granulation tissue
    1. dispose of dead tissue by phagocytes
    2. CT forms a mass = fibrocartilage callus

                                                     i.     Cartilage matrix

                                                   ii.     Bony matrix

                                                  iii.     Collagen fibers

    1. splint closes the gap


  1. bony callus: ________________ replaces fibrocartilage callus



Ossification: the making of bone

 bones does not harden until growth stops, even then it is constantly being rebuilt

            embryonic skeleton is