Question

______ - creates osteocytes
______ - bone resorption

1. osteoblasts: forms bone cells & secrete bone matrix.
2. osteocytes: mature bone cells
3. osteoclasts: destroys bone cells
4. 1/3 of matrix - glycoprotein & collagen fibers (osteoid)

a. the other 2/3 of the matrix is inorganic salts:
bone hardness
ex. calcium phosphate, calcium hydroxide, calcium carbonate.
osteogenesis - bone development or ossification)
a. intramembranous ossification: when bone forms from fibrous membrane & bone is called membrane bone.

1. results in formation of flat bones & some irregular bones (ex. clavicle & some skull bones)
2. fibrous connective tissue formed by mesenchymal cells (embryonic tissue in the mesoderm that all connective tissues comes from)
3. process involves following steps:

a. formation of spongy bone w/in the fibrous membrane - osteoblasts cluster & begin to secrete organic bone matrix (osteoid) around collagen fibers.
b. formation of the periosteum
c. formation of compact bone plates
b. endochondrial ossification: when bone forms from hyaline cartilage structures & is called cartilage bone. (cartilage is used as a model for bone formation)

1. long & short bones are formed by this process that uses hyaline cartilage as models for bone construction.
2. process begins in 3rd month of development & is more complex than intramembranous ossification because hyaline cartilage must be broken down as ossification proceeds.
3. long bone formation begins in the primary ossification center at the center of the hyaline cartilage shaft.
4. steps include:

i. formation of a bone collar around the hyaline cartilage model. - osteoblasts beneath the periosteum secrete bone matrix on the hyaline cartilage model forming bone collar. primary ossification begins w/ infilteration of blood vessels.
ii. cavitation of the hyaline cartilage shaft. invasion of internal cavities by the periosteal bud & spongy bone formation. - cartilage deteriorates & matrix deposited in cavities - spongy bone formed.
iii. formation of the medullary cavity.
iv. ossification of the epiphyses. hyaline cartilage remains only on epiphyseal plate; promotes longitudinal growth.
______ disk (growth plate) is a band of cartilage between the epiphysis and diaphysis
www.biologycorner.com / biol.co/skeletal - slides

Explanation:

• First blank: Osteoblasts form bone cells (osteoblasts secrete bone matrix and form osteocytes as they become trapped in the matrix).
• Second blank: Osteoclasts are responsible for bone resorption (they destroy bone cells, breaking down bone tissue).
• Last blank: The epiphyseal disk (growth plate) is the band of cartilage between the epiphysis (end of the long bone) and diaphysis (shaft of the long bone), responsible for longitudinal bone growth.

Answer:

1. For the first blank (creates osteocytes): Osteoblasts (since Osteoblasts form bone cells which mature into osteocytes)
2. For the second blank (bone resorption): Osteoclasts (since Osteoclasts are responsible for destroying bone cells, which is part of bone resorption)
3. For the last blank (disk (growth plate) is a band of cartilage between the epiphysis and diaphysis): Epiphyseal (the epiphyseal disk, or growth plate, is the band of cartilage between the epiphysis and diaphysis)