Bone Histology (Lect) Flashcards
What are the two types of bone developement?
Endochondral
Intramembranous
What kind of bone usually developes intramembranously?
flat bones (e.g skull bones)
What happens if blood vessels are near mesenchyme?
they enlarge and will become bone rather than cartilage
How do mesenchymal cells condense yet remain attached to each other?
they maintain their gap junctions
What do mesenchymal cells first differentiate into on their way to becoming bone?
Osteoprogenitor cells
What do osteoprogenitor cells differentiate into?
Osteoblasts
What is osteoid?
a non-mineralized matrix laid down by osteoblasts that later mineralizes into a bone spicule (aka canaliculi)
What happens when osteoblasts become trapped and can no longer divide?
they become osteocytes
Does osteoid stain dark?
NO
What is deposited that causes bone calcification?
hydroxyappetite
What is formed by bone spicules growing together?
Spongy bone
What is absolutely essential for bones to live?
blood supply
What is the osteogenic layer?
The outer layer of osteoblasts that line up on the outside and inside during intramembranous bone formation to lay down compact bone
What are the two layers of periosteum?
The fibrous layer and the osteogenic layer
What type of cell is formed by the fusion of monocytes from bone marrow?
osteoclasts
What hormone accelerates the activity of osteoclasts?
parathyroid hormone (happens when Ca2+ and PO4 are low)
What hormone slows the activity of osteoclasts?
calcitonin
T or F: osteoclasts are mononucleated?
False
Describe the location and activity of osteoblasts and osteoclasts in the widening of bone?
osteoblast must be working to build bone on the exterior
osteoclasts must work to clean away bone on the interior
Increase in bone width is an example of?
appositional growth
T or F: all bones have both spongy and compact bone
True - all bones have this component, it doesn’t matter how it formed
What is the point of having weaker spongy bone in the interior of bones?
it helps reduce bone weight
When the growth plate recedes what is formed?
epiphyseal line
What happens to red marrow as you age?
some of the red marrow may be converted to yellow marrow
How many cells thick is the endosteum?
1 layer thick
How is bone decalcification performed for preparation methods?
acid is used to extract the mineral
What is the consistency of bone that has been decalcified?
tough and rubery, and can be cut like any other tissue
What is the ground method of bone prep?
bone is cut with a diamond saw and ground until its thin enough to see through, no stains are used
What do dark areas in ground bone represent?
air
What are haversian systems?
concentric rings (lamelae) that contain osteocytes in a lacuna
These form around haversian canals that contain and artery and vein
canaliculi permit nutrition to move from artery to cell
T or F: each ring in a haversian system contains a population of osteocytes?
True
What is represented by dark spots on bone that has been ground?
air - where the lacuna that used to contain an osteocyte was
What is volkmann’s canal?
a tunnel that allows arteries and nerves to move perpendicular to the direction of the lamellae
What changes with each new ring of osteocytes thats added to a haversian system?
the collagen fibers are oriented perpendicular to that of the preceeding layer
What type of collagen can be extracted from boiling bone?
type 1
What is the ground substance in haversian sytems/bone matrix osteons?
glycoaminoglycans
What is the perpose of the perpendicular orientation of collagen fibers and glycoaminoglycans in collagen?
makes bone tough
What is the name for the organic component of bone?
osteoid
What makes bone hard? The organic or inorganic component?
The inorganic
What does the inorganic component of bone consist of?
crystals of hyroxyapatite (form of calcium phosphate)
What makes up interstitial lamellae?
old osteon/havarsian systems
What structure is created by the touching of cytoplasmic processes of one osteocyte with another?
Canaliculi
What do the fluid filled canals of canaliculi do?
allow you to feel mechanical stress
act as a shock absorber
What is circumferential lamellae?
lamellae that’s fairly straight and lies on the inner and outer edges of the bone
What lies adjacent to inner circumferential lamellae?
endosteum
What lies adjacent to outer circumferential lamellae?
periosteum
What is makes up interstitial lamellae?
remnants of old osteons
How do you tell the difference in volkmann’s canal and a haversian canal?
haversial canals run vertically in the center of osteons while volkmann’s canal runs horizontally
How can haversian systems be added to the periphery of a young shaft?
- Vessel runs along a ridge in the shaft
- periosteum grows to make ridges higher
- Ridges fuse to make a tunnel?
- PERIOSTEUM of the tunnel becomes ENDOSTEUM
- new endosteal cells grow making a haversian system
Besides periosteum closing grooves to make new haversian systems, how can new ones be created?
Osteoclasts can bore a tunnel through existing bone
How do osteoclasts creat haversian systems?
they start on the surface and dig down to make a groove which grows over with periosteal cells
What type of bone will you find haversian systems in?
haversian systems ONLY
How does spongy bone get nutrition if there are no haversian systems?
the spicules are so narrow that nutrition is supplies from vessels in the endosteum that cover spicules (via diffusion through canaliculi)
Does spongy bone contain lamellae?
Yes, but they are not arranged as osteons (aka haversian systems)
Where is lamellae found in spongy bone?
in the spicules
Describe the periosteum embyonic/ postnatal bone.
outer fibrous layer
inner cellular layer - consiting of osteoprogenitor cells and osteoblasts
Describe the periosteum in adult bone.
No inner and outer layers
Only a flat inconspicuous cellular layer
T or F: adult bone contains a thin cellular layer of periosteum (osteoprogenitor cells) that will form ostoblasts and chrodoblasts when fractured
T
Where can the endosteum be found?
- covers all marrow spaces and lines volkmann’s and haversian canals
T or F: endosteum is thicker than periosteum and contains only collagen fibers
False, it contains reticular fibers and is thinner
What is stage 1 of fracture healing?
- clot forms
- bone cells and periosteal cells near the fracture die
- neutrophils, macrophages, and osteoclasts invade to clean up
What is stage 2 of fracture healing?
- periostal fibroblasts and osteoprogenitor cells from periosteum proliferate
- osteoblasts from endosteum and periosteum lay down spongy bone to and around fractured bone (internal callus)
- external callus formed by periosteal cells that diff. into chondroblasts - makes fibrocartilage
What is stage 3 of fracture healing?
cartilage in callus undergoes endochondral ossification to produce spongy bone
What is stage 4 of fracture healing?
remodeling - by coordinating osteoblast and osteoclast activities
How long does remodeling continue after fracture has healed?
a few years
What is osteomalacia
softening of the bone (adult rickets)
bone is imperfectly calcified
What causes osteomalacia in adults?
vitamin D deficiency
What happens if osteomalacia persists for a long time?
a large part of the skeleton will consist of osteoid
What is osteoporosis?
augmented bone resorption leading to porous bones
T or F: the chemical composition of the bone is altered in osteoporosis?
False - same composition but there is just less of it
you end of with a log of thin spongy bone
What helps slow progression of osteoporosis?
exogenous calcium
What is osteopetrosis?
Bones get dense and heavy
What causes osteopetrosis?
defective bone resorption caused by mutation in genes for osteoclast proton-ATPase pumps or chloride channels
Can osteopetrosis be transmitted to offspring?
Yes
What is osteogenesis imperfecta?
brittle bones
What causes osteogenesis imperfecta?
mutation in collagen type I
What types of cells can periosteum become?
osteoblasts or chondrocytes
