Lecture 4 - bone Flashcards
5 roles of bone
support body mass, facilitate movement, protection, site of hematopoiesis, calcium reservoir.
Similarities of bone and cartilage
hard tissues, contain living cells embedded in matrix, common mesenchymal progenitor cells.
Differences of bone and cartilage
bone heavily vascularized/ cartilage avascular; bone access to blood vessels via canaliculi; cartilage less calcified, uses long-range diffusion.
How is bone a dynamic tissue?
constant remodeling from mechanical stress
Piezoelectric potential
bone deposition and bone reabsorption
Bone matrix’s organic components
Type I collagen fibers, amorphous substance (GAGs, glycoproteins), and osteoid
glycoproteins in bone
osteonectin, osteopontin, osteocalcin, and bone sialoprotein
Osteonectin and Osteopontin
anchors minerals to collagen & initiate mineralization and promote crystal formation
Osteocalcin & bone sialoprotein
calcium binding proteins
Bone matrix’s inorganic components
Mostly calcium phosphate, hydroxyapatite (holds water), bicarbonate, and fluoride.
2 methods to prepare bone sections
decalcification (only organic components left- flexible) and grinding (keeps inorganic components)
Mesenchymal osteoprogenitor
osteogenic cell. Committed by Bone Morphogenic Proteins (BMPs) - osteogenin. Differentiate into osteoblasts. Can self renew.
Osteoblast
occur on the periphery. Secrete the osteoid which is the newly deposited material. Abundant RER and golgi. Secretion activated by GH (somatotropin), sex steroids.
Osteocyte
when osteoblasts secrete so mluch osteoid, they become encompassed by it (terminally differentiated). Reside in lacunae.
Osteoclasts
reabsorb calcium.. Formed by a fusion of monocytes. Multinucleated.
Osteoid
deposition of osteoblast cell layer and existing bone. Stains a lighter color on the edge since it is more concentrated in inorganic material.
Canaliculi
canals connecting osteocytes (gap junctions)
2 modes of osteocytic osteolysis regulation
Parathryoid Hormone and Calcitonin
PTH
increases resportion. indirectly stimulates by binding to receptors on osteoblasts which will stimulate osteoclast activity
Calcitonin
descreases resportion
Where are Macrophages located and whats feature does it have?
Howship’s lacunae and a ruffled border to increase surface area.
2 modes of osteoclast function
focal decalcification by acidification (H reacts with calcium to free it) and by extracellular digestion by enzymes (digests collagen and other organic material).
3 parts of bone
periosteum, endosteum, and bone proper
periosteum
Pheripheral. Made of fibrous (outer fibrous layer and highly vascularized) and osteogenic (osteoblasts and osteogenic cells) components
Endosteum
Thin single layer (progenitor cells, osteoblasts, osteoclasts), line bones internal surfaces (trabeculae, H canals), and important for nutrition and maintenance
Bone proper
mineralized components of bone
Attachment of peiosteum to bone
collagen fibers bundles called Sharpey’s fibers
Where is the point of origin for Volkmann’s canals
periosteum
Uncommitted mesenchymal precursor if vascular or avascular
Vascular - osteoprogenitor
Avascular - chondroprogenitor
2 structures of bone proper
woven and lamellar
Woven bone
primary or immature bone. random disposition of collagen fibrils, amorphous calcium phosphate. seen in development and repair
Lamellar bone
secondary or mature bone. Organized disposition of collagen fibers - cancellous or compact
Cancellous bone
spongy bone. Network of irregular lamellae (trabeculae) with bone marrow in between
Compact bone
cortical bone. Forms diaphysis of long bones and thin layer around epiphyses and skull. Highly organized
5 locations where no cancellous bone
flat bones, alveolar bone around teeth, short bones, epiphyses & diaphysis of long bones
Anastomose
fusion of trabeculae trapping blood and lymph vessels. Will cause spongy bone to go to compact bone.
Haversian system
cylindrical columns of 4-15 concentric lamellae surrounding a canal with blood & lymph vessels and nerves
Osteon
Haversian system
Volkmann’s canals
allow blood vessels to go from the outside of the cell to the interior of the bone.
Osteoblast and calcification
Osteoblasts secrete osteoid and calcium binding factors which facilitate the precipitation of calcium phosphate.
Factors secreted by osteoblasts
alkaline phopshatase (promotes accumulation of inorganic phosphate in the osteiod); osteonectin and osteocalcin (high affinity calcium binding proteins)
Why is bone remodeling important?
deposition allows for high vascularity; Resorption allows for formations of canals or morrow cavities; shapes bones; response to mechanical stress; maintain calcium homeostasis.
Osteoporosis
Resorption > deposition
Osteopetrosis
Deposition > resorption
Vit C deficiency
affects production of collagen
Vit D deficiency
decreases uptake of calcium from GI tract.
Vit A deficiency
slow bone growth, can cause premature epiphyseal closure
Vit A excess
slow cartilage growth and accelerated ossification
Growth hormone deficiency and excess
deficiency - dwarfism
excess - gigantism (children), acromegaly (adults)
Sex steroids
influence time of appearance of ossification centers during development
Hyperparathyroidism
excess PTH thus bone mass loss, fragile bones, increase in circulating calcium (goes to kidney)
2 types of ossification
intramembranous and endochondral
intramembranous ossification
differentiation of mesenchymal cells into osteoblasts then osteocytes. occurs in vascularized areas.
endochondral ossification
replacement of cartilage with osteoblasts and osteocytes (seen at articular surfaces).
Sequence of events in intramembranous ossification
Mesenchymal condensation, appearance of blood vessels, differentiation into osteoblasts, mineralization by osteocytes, spicules/trabeculae formed, interweaving of trabeculae.
Way spongy bone is converted to compact bone in a Haversian canal
Intramembranous.
Type of cartilage that is a template for endochondral ossification
hyaline cartilage
Steps of endochondral ossification to form primary ossification center (diaphyseal)
mesenchymal condensation, differentiation into chondroblasts, small hyaline cartilage, capillaries penetrate perichondrium and creates periosteum, formation of subperiosteal bone collar (intramembranous), cartilage degenerates, blood vessels enter,s, then endochondral ossification.
Ossification important for width of bone
intramembranous
Ossification important for length of bone
endochonral
Steps of endochondral ossification after secondary ossification center (epiphyseal)
diaphysis - bone collar grows toward ephiphyses, spongy bone formed in center, marrow cavity enlarges; epiphysis - growth at growth plate (5 distinct zones); spongy bone replaces woven; second secondary ossification starts at epiphysis.
Adult bone
epiphyseal cartilage is no longer present, compact bone @ diaphysis, spongy @ epiphysis, yellow (adipose) marrow, periosteum surrounds shaft, articular cartilage with no peichondrium
5 zones of bone growth
resting zone, proliferating zone, maturing (hypertrophic) zone, calcifying zone, and ossifying zone
Proliferating zone
mitotic zone. Osteoblasts are proliferating in response to growth hormone (lengthening of bone)
Mature/hypertrophic zone
when the cells rupture, calcium migrates into the trailing edge and then start to deposit spongy bone.
Bone repair
oxygen supply interrupted, fibroblasts/macrophages, chondrogenic pathway to form cartilage bridge, blood vessels reappear, which leads to ossification
Synarthrose joint
joint with little or no movement
syndesmosis joint
joined by dense CT (cranial in young)
synostose
immobilized, fused bones (old skull bones)
synchondrose
joined by hyaline cartilage (rib/sternum)
symphysis
joined by fibrocartilage (pubic symphysis, discs)
Diarthrose joint
synovial/articular joint
2 cells found in synovial membrane
A cell - phagocytic
B cell - secrete synovial fluid
Tendon
muscle to bond TMB
Ligament
bone to bone LBB
