Bone Flashcards
What are the two main purposes of bone?
structural support and calcium reservoir
What are the three cell types in bone?
osteoblasts
osteocytes
osteoclasts
What type of fiber is the bone matrix made of?
type 1 collagen
along with the minerals = Ca, Mg, Fe, and Sr
What surrounds the outside of bone?
periosteum (except on articular surfaces, which is hyaline cartilage)
What cell is largely responsible for the manifacturing of bone? How?
THe osteoblasts
it’s a two-step process:
- synthesis of organic matrix = osteoid (perior to mineralization)
- deposition of inorganic components (alkaline phosphatease secretion and concentrate phosphate ions)
Where are the osteoblasts located?
on the bone surfaces
it looks like a cuboidal epithelia, but it’s not.
Osteoblasts have receptors for what hormone? WHat do they do when it binds?
parathyroid hormone
when it binds, the osteoblasts releases osteoclast stimulating factor to increase osteoclast activity
What will osteoblasts eventually become? Do they lose contact with each other?
They become osteocytes embedded in the matrix. They maintain contact through projections in canniculi - the ends of which form gap junctions
What is the purpose of an osteocyte?
It has reduced protein synthesis, but it’s still important
it plays a role in the maintenance of the matrix and regulation of calcium
What are osteocyte located in?
they are in lacunae within the matrix
Do the osteocytes form isogenous nests like chondrocytes do?
no
WHat occurs via the gap junctions of the osteocyte projections?
cell-cell coordination and nutrient transfer
What are osteoclasts derived from?
monocytes
What do osteoclasts do?
they are large, multinucleated motile cells that take care of bone resoprtion and thus bone remodelling
WHy do osteoclasts have a lot of lysosomes?
because they use lysosomal enzymes to break down and remodel bone
Are osteoclasts mitotic?
no
WHat is the term for a region of resorbed matrix containing an osteoclast?
a howship’s lacuna
What is an osteoclast’s ruffled border?
It’s the outer rim with microvilli that lies against the bont surface
What does the ruffled border do for the osteoclast?
Its membranes pump H+ into the sub-osteoclastic compartment in the howship’s lacuna to lower the pH and liberate the minerals from the bone
the minerals are them taken up by the osteoclasts and delivered to nearby capillaries
True or false: osteoclasts are mononuclear?
false - multinuclear
What are the inorganic components of the bone matrix?
calcium predominates in the form of calcium phosphate and hydroxyapatite crystals
also Mg, Fe, and Sr
What is the importance of keeping the calcium in hydroxyapatite crystals?
it’s a hydrophilic molecule that binds water
this facilitates the exchange of the calcium between body fluids and the crystals
What are the organic components of the bone matrix?
type 1 collagen
ground substance composed of chondroitin sulfate, keratan sulfate, hyaluronate, and glycoproteins
What are the 3 glycoproteins in the bone matrix
in general what is their purpose?
osteocalcin, osteopontin, osteonectin
they have multiple binding sites on them to bind osteocytes, osteoblasts, type 1 cllagen, and the hydroxyapatide crystals together to make a nice architectural unit in the bony matrix
What are the 4 types of bone?
- cancellous (spongy)
- compact (dense)
- primary bone (woven)
- secondary bone (lamellar bone)
What is cancellous bone like? Where is it located?
It’s comprised of spicules (traveculae) of bone united to form a network
located in the interior of bone (like the ends of long bones)
Where is compact bone located?
it’s the outer exterior of bone
Which has haversian systems, primary or secondary bone?
secondary bone
What kind of bone is the diaphysis? WHat kind of bone is the metaphysis?
diaphysis = compact bone
metaphysis = spongy bone
What is the tough CT layer that surrounds the diaphysis?
the periosteum
What is the CT layer on the internal surfaces of the diaphysis? WHat is just below that?
the endosteum
beneath that is the marrow cavity
What kind of bone is in the medullary cavity of the epiphysis? What is the cap made of?
the medullary cavity is cancellous bone and it contains a marrow cavity.
the articular cap is made of hyaline cartilage
At the epiphyseal plate, the periosteum becomes continuous with what kind of layer?
perichondrium (since the epiphyseal plate is cartilage until it closes)
What are the two layers of the periosteum? What’s in each?
the outer layer is the fibrous layer - containing fibroblasts, collagen, and elastin - protects the bone and acts as an insertion site for tendons
the layer adjacent to the bone surface is the osteogenis layer - contains osteprojenitor cells, osteoblasts, and osteoclasts (if there’s remodelling going on)
What serves to anchor the periosteum to bone?
Sharpey’s fibers - collagenous fibers that are very strong and can be quite prominent
What cells are contained in the endosteum between bone marrow and bone matrix?
osteoblasts, osteoclasts and a few osteogenic cells
WHat is another name for haversian system?
an osteon
What does an osteon consist of?
It’s concentric lamellae of bone (usually not more than 10 lamellae/osteon) with osteocytes between the lamellae layers that communicate with each other through canniculi
they have a haversian canal in the center that containes blood vessels, nerves, and lymphtics
Describe the plane of collagen deposition in adjecent lamellae?
the deposition is perpendicular to adjacent lamellae
What are Volkmann’s canals?
They’re vascular passageways that run radially through compact bone (as opposed to the haversian canals that go longitudinally)
note they are NOT surrounded by bone lamellae
What is an interstitial lamella?
a remnant of a partly resorved osteon - they just don’t look complete anymore and they don’t have vessels anymore
What do we call the lamellae that run right beneath the periosteum? Do they go all the way around?
outer circumferential lamellae
they usually don’t completely encircle the bone shaft because of resorbtion
What do we call the lamellae that run just adjacent to the endosteum?
inner circumferential lamellae - usually not complete either
Why is bone development appositional only?
osteocytes are amitotic and calcified matrix can’t expand
What are the two ways an osteon can be formed?
- adjacent to the periosteum, osteoclasts will create a groove in the surface of bone, into which the blood vessles and nerves sink, after which the osteoblasts create new bone on top of them, enclosing in an osteon
- In the internal depths of the bone, osteoclasts will drill a hole in an existing osteon and then osteoblsats will lay down bone from the outside of the hole in.
Which type of bone development will result in compact bone, intramembranous bone formation or endochondral bone formation?
TRICK QUESTION
both intramembranous and endochondral can result in both compact and cancellous bone tissue
What is the precursor in intramembranous ossification? What is the precursor in endochondral ossification?
intramembranous = embronic CT
endochondral = hyaline cartilage
Which bones ar emade through intramembranous ossificaiton?
the skull bones, mandicle, maxilla, and clavicle
What happens first in endochondral ossification?
formation of the bone collar
it’s intramembranous ossification around the diaphysis of the cartilage template
What does the bone collar cause?
it prevents diffusion of nutrients into the cartilage matrix, so it calcifies - the chondrocytes become hypertrophic and die. then the matrix surrounding those chondrocytes gets resorbed.
How and where does the primary ossification center form?
After the cartilage calcifies under the bone collar, you can get penetration by capillaries that bring in osteoprogenitor cells
these develop into osteoblasts and formt he primary ossification center in the diaphysis.
What happens in the primary ossification center?
osteoclasts resorb the cartilage matrix
osteoblasts lay down woven bone first, which is later remodelled into lamellar bone.
bone marrow precursors also arrive.
the bone collar expands and the bone grows longitudinally
Where does the secondary ossification center develop?
it’s ossification of the epiphysis - WITHOUT bone collar formation
WHile growth in the primary ossification center is longitudinal, growth in the secondary ossificaiton center is….
radial
What cartilage does NOT become calcified in the epiphysis?
the interarticular hyaline cartilage
What are the 5 zones of the epiphyseal plate?
- resting zone (normal hyaline cartilage)
- proliferative (high mitotic activity with column s of isogenous nests (stacks of pancakes))
- hypertrophic zone (glycogen accumulation - cells chondrocytes enlarge)
- calcified (chondrocytes die - deposition of hydroxyapatie)
- ossification (osteoblasts and bone matrix appear)
label…
In synovial membranes, what secretes the synovial fluid? What is it made of?
the type B fibroblasts secrete synovial fluid, which is composed of hyaluronate and glycosaminoglycan
Besides the fibroblasts, what other cells make up the synovial membrane? What does this look like?
macrophages (type A cells)
together, they look like a squamous epithelium, but it isn’t
What 4 things will induce “plasticity” of bone?
stress induced remodeling (braces)
fracture
disuse (loss of bone density)
hormone changes
What two hormones are involved in calcium homeostasis? What secretes them?
secreted by the thyroid….
parathyroid hormone increases calcium resorption by stimulating osteoblasts to stimulate osteoclast activity
calcitonin promotes calcium deposition by inhibiting osteoclast activity
What happens to the bone in scurvy?
it’s a vitamine C deficiency so you don’t get proper hydrosylation of proline resieus and the alpha chains of tropocollagen can’t form stable microfibril aggregates
improper collagen synthesis
this results in weakness of epiphyseal plates and diaphysis
What is Rickets?
It’s a vitamin D deficiency in children
it leads to improper absorption of calcium from the intestin and they thus have a functional clacium deficiency
this results in incomplete bone matrix calcification and the spicules will distort under strain causing bone deformation
What is “adult rickets”?
osteomalacia
it’s prolonged vitamin D deficiency so you have deficiency calcium
this causes deficient calcification of new bone and a gradual decalcification of existing bone.
You don’t get bone distortion with this one, but they do get weaker
What happens in osteoporosis and what causes it?
bone tissue is diminished due to hormone changes causing osteoclast activity to outstripp the osteoblast activity
lack of estrogen
