Lecture 8: Bone Flashcards
The structure of individual bones is designed to provide maximum resistance to ____ ____ while maintaining the least _____ _____.
Mechanical stress
Body mass
Applied histology definition of bone
Specialized connective tissue consisting of cells embedded within a gel-like substance that becomes mineralized
Bone has the property of marked ____ and _____ while retaining some degree of _____
rigidity
strength
elasticity
Bone is considered both a ____ and an ____ because
tissue
organ
an organ is a group of tissues which perform a specific function or group of functions
4 functions of bones
- Support/protect
- Shape/movement
- Source of calcium reserve (99%) and storage of other inorganic ions
- Active participation in the maintenance of calcium homeostasis in the body
To acommodate changes related to mechanical stresses and demands on calcium homeostasis, bones are in a dynamic state of
growth and resorption throughout life
Bone is composed of
Cells and an organic extracellular matrix containing primarily glycoproteins and collagen fibers called the osteoid
Osteoid rapidly undergoes mineralization by
deposition of inorganic salts, mainly calcium hydroxyapatite crystals, to form bone
The bone matrix growth factors play an important role in
bone development
modeling
remodeling
Bone composition percentages
- 9% water
- 22% organic matrix
- 69% inorganic matrix
Organic matric is ___% collagen which is responsible for
95
tensile strength
Collagen in organic matrix is mainly type
I
Bone organic matric contains
- Sulfated GAGs like chondroitin and karatan sulfate
- Glycoproteins such as alkaline phosphatase, osteonectin, and ostepontin
Inorganic matrix is mainly composed of
Hydroxyapatite crystals deposited within collagen fibrils to enhance tensile strength
How are the microcrystals of hydroxyapatite formed?
Calcium phosphate reacts with calcium hydroxide
The main minerals of the bones
- Calcium phosphate (85%)
- Calcium carbonate (10%)
- Amounts of Na, Mg, and Fe are substantial but constitute less than 5% of bone total
What provide the framework and necessary tensile strength?
Collagen fibers produced by osteoblasts
What serve as carriers for minerals?
Proteoglycans of the bone (osteoid) embedded in the collagen fibers
How does the bone matrix harden?
By deposition mainly of hydroxyapatite
Two bone envelopes
Periosteum
Endosteum
Periosteum
- A fibrous connective tissue layer that covers outer/external surface of bones
- Site of insertion of muscles, tendons, and ligaments
Endosteum
-Inner delicate connective tissue surface of the bone - lines the trabeculae of the spongy bone
Immature bone cells originating from osteoprogenitor cells
osteoblasts
Osteoblasts are responsible for
synthesis and secretion of collagen and organic compounds of the extrallcellular matrix of bone (osteoid)
Osteoid quickly mineralizes and osteoblasts are trapped as
osteocytes
