Bone Flashcards
What are the functions of bones?
Support
Protection
Movement
Electrolyte balance
Blood formation
What is the only way that bone grows?
Appositional mechanism
What is the macroscopic structure of the long bone?
Diaphysis, proximal and distal epiphyses (growth plate), metaphysis
Marrow cavity
Articular cartilage
Periosteum
Endosteum
Marrow spaces
Marrow cavity
A central space that contains bone marrow cells
Articular cartilage
The joint surface between 2 bones
Periosteum of the long bone
An outer covering that contains bone marrow cells and an inner osteogenic layer of stem cells
Absent at articular cartilage
Endosteum
Marrow spaces and trabeculae of spongy bone
Macroscopic structure of the cranial bone (flat)
Outer plate
Diploe
Inner plate
Periosteum of the cranial bone (flat)
Covers the outer surface of both the inner and outer plates
The inner plate is fused with the duramater of the cranial cavity
How are the inner surfaces of both plates in a cranial bone lined?
Marrow spaces of the diploe and are lined by endosteum
Microscopic structure of the compact bone
Ground substance containing inorganic calcium and phosphate salts (hydroxyapatite)
Cells
Type 1 collagen in the matrix (lamellae)
How are the lamellae of the compact bone classified as?
Outer circumferential under the periosteum
Inner circumferential under the endosteum
Concentric (osteons)
Interstitial between osteons
What cell types are in the compact bone?
Osteoprogenitor, osteoblasts, osteocytes and osteoclasts
What is the bone organic bone matrix made of?
Type 1 collagen fibers
Non mineralized (chondroitin sulfate and keratin sulfate) ground substance
Metaphysis
Area involved in elongation between diaphysis and epiphysis in growing bones
What is the bone inorganic bone matrix made of?
Hydroxyapatite (calcium and phosphorus) mineralized osteoid
What is spongy bone called in flat bones?
diploe
Primary/ Woven bone
Newly formed, immature bone, rich in osteocytes
Osteoclasts and osteoblasts numerous in surrounding endosteum
Low mineral content
Where isn’t primary bones replaced in adults?
Tooth sockets, insertions of some tendons
What is the first bone tissue to appear in embryonic development and in fracture repair?
Primary bone
Secondary (Mature) Bone
Found in adults
Lamellar bone (calcified matrix, 3-7 micrometers thick)
Matrix organized as lamellae
Osteon
Haversian System
Concentric body lamellae surrounding small Haversian canal with blood vessels, osteocytes, nerves and loose CT
Cement line
Outer boundary, collagen rich layer of osteon
Haversian Canal
Single trophic unit in osteon
Involves the common nutrition
(circle in the middle of the bone)
Volkmann’s Canal
Connects adjacent Haversian canals
Connect the periosteum and endosteum bringing blood vessels to the bone
(long skinny tunnels)
Mature Osteon
Lined by osteoprogenitor cells
Haversian canal is narrow
Regular lamelle
React to stain
What are the 3 types of osteons?
1) mature osteons
2) forming osteons
3) Resorption osteons
Interstitial systems
Remnants of osteons after remodeling
Present between regular osteons
Irregular lamellar structures without central Haversian canal
Forming osteons
Haversian canal lined by osteoblasts
Resorption osteons
HC lined by osteoclasts
HC wide and irregular
Remodeling of bones
- Resorption of osteons
- Osteoblasts appear in the resorption cavity and start building a new generation of osteons
- Remnants of the previous osteon forms in interstitial system
Continues throughout life
Appositional Growth
Occurs when new bone tissue is deposited on the surface of the bone (thickening)
Osteoprogenitor cells
Solid matrix
Interstitial Growth
Produces longer bones as the cartilage lengthens and is replaced by bone tissue
Addition within
Chondroblasts
Denser matrix
Osteoprogenitor Cells
Stem cells found in the endosteum, inner layer of the periosteum and the Haversian canal
Osteoprogenitor cells differentiation
They multiply and:
1) become osteoblasts at sites where new bone must be synthesized
2) Become chondroblasts in an environment of low oxygen tension
Osteoblasts
Bone forming cells
Found in same location as osteoprogenitor cells and bone surface
Synthesize osteiod matrix
Large, rounded branched cells, basophilic
Osteocytes
Mature osteoblasts surrounded by their own matrix
Lie in lacunae interconnected by canaliculi (communication and exchange)
Branched
Osteoclasts
Bone eating cells found on the bone surface
Multinucleated, derived from monocytes
Lie in Howship’s lacunae (enzyme eroded depressions)
Osteoid
Uncalcified matrix made of type 1 collagen and ossseomucoid
What stimulates osteoprogenitor cells to differentiate into osteoblasts?
Stress and fractures –> which build a new bone
How do neighboring osteocytes in a mature osteon connect with each other?
Via cytoplasmic process that lie in the canaliculi and this allows osteocytes to get nutrients from distant vessels
What are the functions of osteocytes?
Maintenance of bone density, homeostasis, and blood concentration of calcium and phosphate
Calcium continuously renewed by osteocytes
Ruffled border
On the side of the osteoclast facing the bone surface
Composed of finger-like projections of the cell membrane extending to the Howship’s lacunae
Increase the surface area of bone resorption
What are the functions of osteoclasts?
Resorption, remodeling and bone repair
Osteogenic cells
Mesenchymal stem cells in the periosteum and endosteum
Small oval/elongated, pale cytoplasm and oval nuclei
Characteristics on the osteoclasts
Large, multinucleated
Acidophilic
Ruffled border facing bone marrow
Clear zone
An area of cytoplasm that seals off an acidic micro-environments containing lysosomal enzymes
Bone resorption occurs here
What is tranfered into the clear zone?
Collagenase and protons from osteoclasts, that break down collagen fibers and calcium salts
What phagocytizes the remnants of bone resorption?
Osteoclast
What is the function of calcitonin?
Decreases serum calcium levels and deposits it in bone through a reduction in osteoclastic activity
Encourages bone tissue formation that can b used in clinical treatment of osteoporosis
Produced by parafollicular cells of the thyroid gland
Osteoporosis
Porous bone
Disease where density and quality of bone are reduced
Old age and post-menopausal women
Bone resorption increases more than bone formation
Osteogenesis
Formation of bones
1) Intramembranous ossification
2) Endochondral ossification
Spongy Bone
Composed of interconnected trabeculae that surround cavities filled with bone marrow
Bone matrix with osteocytes
What is each trabecula lined with in spongy bones?
By endosteum containing osteoprogenitor cells, osteoblasts, osteoclasts
Bone marrow
Soft tissue present in the marrow cavity of a long bone and in the spaces of a spongy bone
Red and yellow types
Red bone marrow
Marrow cavity of all bones in young animals that are filled with red marrow (myeloid/ hematopoietic tissue)
Yellow Bone marrow
In adults the red marrow will turn into fatty yellow tissue except in the skull, vetebrae, sternum and pelvic girdle
Intramembranous ossification
Occurs in embryonic development
Develop in fibrous sheets called trabeculae
Mesenchymal cells lining trabecula in the presence of blood vessels differentiate into osteoblasts, which synthesize osteoid, then is calcified
Endochondral ossification
Matrix of preexisting hyaline cartilage is eroded and replaced by osteoblasts producing osteoid
What are the trapped osteoblasts in the calcified matrix?
Osteocytes
How is spongy bone converted to compact bone?
When the trabeculae at the surface of the bone continue to grow and calcify until the spaces between them are filled in
What are some examples of intramembranous ossification?
Flat bones of the skull
Part of the scapula and pelvic girdle
Mandible
Maxilla
Calvicle
Steps for endochondral ossification
1) Formation of periosteal collar in the periphery
2) Hypertrophy of cartilage cells in the center of the cartilage models
3) Calcification of cartilage matrix
4) Degeneration of cartilage cells
5) Infiltration of periosteal bud carrying blood vessels and osteoblasts in the middle of the cartilage matrix
6) Replacement of woven bone by lamellar bone
This repeats until until the entire cartilage is replaced by bone except epiphyseal plate
Zones of the epiphyseal plate?
Reserve cartilage cells (resting)
Zone of cell proliferation
Zone of hypertrophy
Zone of calcification
Zone of ossification
What way CAN’T bones grow?
Interstitial mechanism because cells cannot multiply in a calcified matrix
Steps in intramembranous ossification
1) capillaries grow into mesenchyme and release oxygen
2) surrounding mesenchymal cells round up, differentiate into osteoblasts and form osteoid
3) osteoid mineralizes. Osteoblasts become osteocytes
4) bone spicules form and enlarge to form trabeculated of immature bone
5) A single plate (table) of bone are formed
6) immature bone is replaced by mature bone
7) remodeling continues, and two tables of bone are formed
8) The two tables are separated by Diploe
Parathormone (parathyroid hormone)
Increases osteoclastic activity which increases bone lysis, release of calcium and PO4
Growth hormone
Produced by the anterior pituitary gland
Stimulates overall growth of the body
Excess growth hormone during growing years
Gigantism
Excess growth hormone during in adult years:
acromealgy
Deficiency of growth hormone during growing years?
Dwarfism
Osteomalacia
Calcium deficiency in adults
Deficient calcification of newly fromed bone and decalcified of already formed bone
Rickets
Calcium deficiency in children caused by vitamin D deficiency
In children
Deformed epiphyseal plates
Osteopetrosis
Genetic disorder characterized by heavy bones due to defective osteoclastic activity
Bone Fracture healing
Blood vessels torn bleed which clots to produce a large hematoma.
Clot is gradually removed by macrophages and replaced by a soft fibrocartilage- like mass ( procallus tissue) rich in collagen and fibroblasts. If broken, the periosteum re-establishes continuity over this tissue.
Procallus tissue is invaded by regrowing blood vessels and osteoblasts.
Later( few weeks) fibrocartilage is gradually replaced by trabeculae of primary bone, forming a hard callus throughout the original area of fracture.
Primary bone is remodeled as compact and cancellous bone in continuity with the adjacent uninjured areas and fully functional vasculature is re-established
