Skeletal System: Bone
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- general considerations
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
True bone found in every vertebrate class except the chondrichthians; absence appears to be a secondary loss
- bony fish
bone is composed of acellular tissue; no osteocytes nor osteoclasts; largely matrix layered (lamellar bone)
- amp., rep, 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)
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
What is a difference between most bony fish?
they lack a matrix
In amphibians, reptiles, and birds, __.
the activity exists
immature bone cell; secretes matrix and, like cartilage, there a lot of matrix
the cells reside in that matrix
In bone, what are the two components of matrix?
- fiberes: mostly collagenous
- amorphous ground substance: some kind of mucopolysaccharide; active in mitosis and synthesis of the matrix
At some point, what happens to osteoblasts?
they mature and become osteocytes
- What are the two kinds of bone?
Dermal (membrane/-ous) bone: bone forming in and upon a connective tissue membrane
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
Examples of dermal bone.
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
In mammalian bones, there are __ for it.
Most mammalian bones: __
two histological orientations
random array of osteocytes embedded in matrix; not highly organized; may be lamellar or concentric; osteocytes located on line of concentric circle
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 the osteocyte
Location of Haversian systems?
only found in shafts of long bones of mammals; and its there that Haversian systems make up--in the diaphysis and what not; provides the greatest amount of strength of bone
What are the steps of the formation of membrane (dermal) bone?
Cells and matrix
–immature bone cell; active in division in mitosis and it secretes the matrix; has extensions that stick of the cell
–mature cell that resides within a lacuna in the matrix; once it is hardened, the extensions are brought back in and what appears in the matrix are canals
–cell that resides in the periphery of bone right underneath the periosteum; involved in bone resorption
–Inorganic components- 60% is inorganic hydroxyapatite (the calcium salts), which also provide strength, but compressive type of stress
––Organic component- fibers--collagen
Forms of bone
- compact (Dense)
- cancellous (spongy)
- all solid bone
- can have a canal running through it, as well as canaliculi
- no honeycomb appearance
- much stronger, which is why it is used to protect spongy bone
- osteocytes and matrix
- spicules or spears of bone and several clear spaces, which can be filled with yellow marrow (fat) or red marrow (hemopoietic tissue, which gives rise to RBCS)
- whereer you have spongy bone, it is covered by a thick layer of compact bone because it can easily be broken
All bone that is made is __ ad then it gets __
- remodeled to become compact
In terms of classifying bones, what are the classifications?
- Length > Width
- 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
- epiphyses are spongy bone covered with a thin layer of compact bone
In some long bones, what is present?
- a cartilage plate called the epiphyseal plate
- it is hyaline cartilage and allows for the lengthening of long bones; at the end of the growth period, that cartilage becomes bone
- have a similar to equal length and width; they are spongy bone covered with a thin layer of compact
- carpals are examples
really compact on the outside, compact on the inside, and a thin layer of spongy in the middle (flat bones of the skull are examples)
bones that don't fit into the other categories (ex: patella); mainly spongy covered by a thin layer of compact
a longitudinal array of bone found in long bones of many mammals
composition and organization -- look up
means small canals, all of which allow for diffusion of materials between cells and between blood, which is in the center canal
If it were solid bone, nothing could diffuse through it; canals allow for communication
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