Bone Flashcards
What are the functions of the bone?
- Protect other organs
- produce hematopoietic cells, store minerals,
- Provide structure and support the body
Describe the weight of bone and flexibilty
they are lightweight, but strong yet have internal flexibility because of spongy bones (spicules with spaces between)
Trabecular Bone
** cancellous/spongy bone
large surface area; bone marrow
Cortical bone
** Compact bone
more dense than the tubercular bone
Label all the letters
T- Trabecular
C - Cortical bone
E – epiphysis
D -diaphysis
M – metaphysis
P – physis = growth plate
AC – articular cartilage
Label each line
What is the structural organization of bone tissue
Lamellar bone
Woven bone
Lamellar Bone
strong mature, forms slowly
collagen fibers in matrix arranged in layers (lamellae) resulting in strong mature bone (osteoid)
organized into osteons (Haversian systems) in mature cortical and trabecular bone
Woven bone
weak immature, produced quickly
disorganized arrangement of collagen fibers
present at sites of rapid bone formation (e.g. fracture repair, inflammation, neoplasia)
◦ E. g. periosteal new bone or reactive bone
Osteon
functional unit of lamellar bone located in circles around the central canal (Haversian) and in the interstitial bone between the circles of bone
India ink has been used to
Demonstrate the canaliculi and lacunae
Where are haversian canal seen
at the center of each osteon `
Where is Osteon found?
Osteons are in mature bone = lamellar; not woven bone Located in cortex, trabeculae of bones
What are the cellular elements of bone tissue
Osteoblasts
Osteocytes
Bone lining
Osteoclasts
Where are osteoblast, osteocytes and bone linning cells derived from?
Derived from osteoprogenitor cells
Osteoclasts origin
Monocytic origin
Osteoblast
Produce osteoids and initiate its mineralization.
Secrete type 1 collagen
Positioned external to osteoid matrix
Differentiate to become osteocytes
Some osteoblasts (ob) become surrounded by osteoid and embedded in the bone (osteocytes)
Osteocytes
Most abundant cells
Reside in lacunae surrounded by mineralized
matrix (long filipods to increase their cell area)
Regulate exchange of Ca2+ and other ions between the bones
Fluid and ECF under influence of parathyroid hormone`
Osteoclasts
Bone resorption
Reside in shallow pits (Howship’s lacunae)
Acid demineralizes bone and enhances activity of acid hydrolases released from osteoclasts (extracellular digestion)
What stimulates osteoclast activity
PTH
Label this image
Osteoblasts are rounded, form a single row of cells along trabeculae.
Osteocytes are thinner and located within lacunae embedded in bone.
Osteoclasts are multinucleated cells located along trabeculae and will resorb bone under stimulation of cytokines secreted by osteoblasts or inflammatory cells
System hormones affecting bone
Parathyroid hormone (PTH)– promotes bone resorption
1,25-dihydroxyvitamin D3 – required for normal bone growth and mineralization; also stimulates bone resorption
Calcitonin – inhibits bone resorption
Glucocorticoids – inhibit formation and stimulate resorption
Estrogen – inhibits bone resorption Insulin, growth hormone, androgens and thyroid hormones are also involved in bone metabolism
Osteoid Organic components contain (bone matrix)
Type I collagen – main component of osteoid (~90%)
Osteonectin – involved in mineralization
Osteocalcin – vitamin K-dependent; also involved in mineralization
Proteoglycans – less abundant than in cartilage matrix
Growth factors – e. g. BMPs, IGFs, TGFs, FGFs
How does bone formation occur?
Endochondral bone formation is preceded by hyaline cartilage. It occurs when cartilage differentiates, matures, mineralizes, die and is scaffold that osteoblast resides on
What produces osteoids
Osteoblasts
What zone are osteoid produced and bone produced?
Zone of primary spongisosa and is gradually mineralized into mature lamella bone
Matrix mineralization
In bone, osteonectin and osteocalcin absorb to type 1 collagen and bind Ca2+
Osteoid is not mineralized immediately after depostion - failure to mineralize bone produce rickets = osteomalacia (can result in soft bone fracture)
Intramembranous ossification
↑WIDTH; adult
Bone formed from mesenchymal tissue in periosteum
Occurs in flat bones of skull and pelvis and on
all periosteal surfaces throughout life
Responsible for the growth of bones in width
NO cartilage needed first
Endochondral ossification
↑LENGTH; young
Bone formed from hyaline cartilage precursors in PHYSES
Most bones develop by this method (appendicular, axial and base of skull)
At physes responsible for growth of bones in length
Hyaline cartilage precedes and is scaffold
Bone blood supply
Blood enters the marrow cavity of bones through nutrient, metaphyseal and epiphyseal arteries.
In young animals, the cortex is supplied mainly from the endosteal surface and exits via periosteal veins (i. e. blood flows centrifugally).
With age, the cortex becomes increasingly dependent on periosteal arteries.
