Bone Lecture 1 Flashcards
Fxns of bone
Structural support
Protection of vital organs
Hematopoiesis (red bone marrow)
Reservoir for Ca2+ (calcium) and PO4- (phosphate)
Mechanical levers for movement
Storage of adipocytes (yellow bone marrow)
What makes up Long Bones?
Epiphysis Metaphysis (growth plate) Diaphysis Periosteum Endosteum Compact/cortical bone Spongy/Trabecular bone Articular cartilage Red & yellow marrow
Characteristics of flat/short/irregular bones
Two outer plates Cortical bone (dense)
Diploe (middle layer)
Spongy bone
Contains red marrow
Locations
Skull, ilia, ribs, sternum
Long Bone types
Bones of extremities
Short Bone types
Cube-shaped bones of wrist/ankle
Irregular Bone types
vertebrae, sacrum, mandible
Flat Bone types
cranium, sternum, ilium, scapula
Sesamoid Bone types
Bones within a tendon (patella)
Osteoblasts characterisitics
Located at surfaces of bone tissue
Cells are side by side, similar to an epithelial cell layer
Actively synthesize osteoid = organic matrix of bone
What do osteoids contain?
Type I collagen
GAGs, PG aggregates
Glycoproteins – osteonectin, osteocalcin
What do osteoblasts create?
hydroxyapatite crystals (calcium and phosphate) to “calcify” (harden) the matrix
Osteocytes
Osteocytes are osteoblasts that have become surrounded by calcified organic matrix
Calcification occurs “around” osteocyte, creating a lacuna
Osteocytes function to maintain matrix of bone
Osteocyte maintains small amount of non-calcified matrix at its immediate periphery within the lacuna
Osteocytes fxning
Osteocytes have cytoplasmic processes extending from the cell
Calcification of matrix “around” these processes creates canaliculi (small canals)
Osteocytes use canaliculi to form connections and gap junctions with adjacent cells
Allows easy nutrient exchange between cells
Osteoclasts
Multinucleated (5-50 nuclei)–highly active
Motile-never locked in a matrix
Derived from blood monocytes
Located in Howship’s lacunae when actively resorbing bone
Fxn of Osteoclasts
Function as bone macrophages to resorb matrix of bone during bone remodeling
Resorption (break down) of bone
Ruffled Border of osteoclasts importance?
necessary for proper bone resorption
Creates a microenvironment for demineralization and organic matrix removal
Site of adhesion of the osteoclast to the bone matrix
Bone Resportion process
Osteoclast secretes collagenase to digest organic matrix of bone (especially collagen)
Osteoclast also pumps protons (acid) into lacunae to promote localized digestion of ECM proteins
Resorption is controlled by cytokines and hormones
Thyroid hormone, calcitonin – reduce activity
Osteoblasts have receptors for parathyroid hormone (PTH); PTH causes osteoblasts produce osteoclast stimulating factor –increase activity
Bones ECM organic components
Osteoid
Type I Collagen
Ground substance (GAGs, PGs, glycoproteins)
Bones ECM inorganic components
Minerals
Calcium and phosphorous salts
Hydroxyapatite crystals
Osteoid: Un-calcified bone matrix
Type I collagen in large fiber bundle form
Ground Substance
GAGs - Chondroitin-4-sulfate
Glycoproteins = osteocalcin, osteonectin & bone sialoprotein
Each aids in process of calcification of bone
Removal or loss of osteoid of bone results in:
Brittle bone
Bone inorganic components
Calcium and Phosphorous Salts
50% of dry weight
50% are replaced each year in bones
Hydroxyapatite crystals (combination of salts)
Ca10(PO4)6(OH)2
Give bone its rigidity
De-calcification of bone results in
Flimsy/rubbery bone
Periosteum/Endosteum
External and internal surfaces of bone are covered by layers of bone-forming cells
Periosteal fibroblasts along with their associated dense connective tissue ECM
Functions:
Nutrition of osseous tissue
Continuous supply of new osteoblasts necessary for maintenance, repair and growth of bone
Periosteum outer layer
Fibroblasts
Collagen fibers (mostly type I)
Sharpey’s fibers - Bind periosteum to bone
Periosteum inner layer
Osteoprogenitor cells
Fibroblast-like cells with the potential to divide and differentiate into osteoblasts
Endosteum fxn
Lines all internal cavities within the bone
Provides nutrient supply to bone cells
Single layer of flattened osteoprogenitor cells
Small amount of loose connective tissue
Some collagen fibers, minimal ground substance
Osteoprogenitor cells provides a reservoir for new osteoblasts for bone maintenance, growth and repair
Primary Bone
Immature or woven bone
First to appear in fracture repair and in embryonic development of bone
Organic matrix fibers (collagen) are irregularly arranged
Secondary Bone
Mature or lamellar bone
Collagen fibers and cells have a lamellar (layered) arrangement
Primary bone purpose and characterisitics
Type of bone that is produced when bone is initially formed; occurs in adults only during fracture healing
Replaced by mature, lamellar bone as fracture repair progresses
Characteristics:
Irregular array of collagen fibers
Lower mineral content compared to lamellar bone
Higher proportion of osteocytes vs. lamellar bone
Lamellar (mature) bone
Outer circumferential lamellae
Inner circumferential lamellae
Around marrow cavity
Interstitial lamellae
Between the 2 circumferential systems
Haversian System Components: Haversian Canal
Parallel to long axis of bone
Form the central point of Haversian systems
Haversian System Components: Volkmann’s Canal
Oriented perpendicular to long axis of bone
Connect blood supply between Haversian systems
Haversian System – Fiber Orientation
In each lamella of the system, collagen fibers are oriented parallel to each other
Fibers orientation in adjacent lamellae may change up to 90º
Formation of collagen fibers within lamella imparts significant mechanical strength to bone for resisting tensile forces in many directions
