May23 M2-Histo 2 Flashcards
types of bone formation (names) (+ other name given to the bone bc of that) depending on type of bone formed (primary woven trabecular vs secondary lamellar same orientation fibers)
- primary bone = intramembranous ossification. (so also called intramembranous bones)
- secondary bone = endochondral ossification (so also called endochondral bones or long bones)
intramembranous ossification where and what
- within a periosteal membrane (periosteum)
- direct mesenchymal condensation and osteoblast differentiation (mes cell to osteoprogenitor to osteoblasts)
endochondral ossification is what
bone growth during development
- cartilage-related
- requires initial cartilage model (anlagen) to degenerate in its center, have its ECM calcify and then serve as substrate for future osteoblasts to attach and form bone on top
bones doing intramembranous ossification
- flat bones*
- cranial vault (top of the skull)
- mandible (lower jawbone)
- maxilla (upper jawbone)
- part of clavicle
- occipital, temporal, parietal bones
bones doing endochondral ossification
- long bones*
- femur
- tibia
- radius
- ulna
- vertebrae
where intramembranous ossification occurs
within plates of mesenchymal cells
intramembranous ossification step 1 and 2
- group mesenchymal cells diff into osteoblast forming a primary ossification center (bone blastema)
- osteoblasts synthesize ECM, become encapsulated osteocytes + spicules are formed
charact of the first step of intramembranous ossification (appearance)
bone blastema or primary ossification center
- mesenchyme cells look like fibroblasts bc they have a stellate apperance with processes going everywhere
- these mesenchyme cells are pluripotential
apperance of bone at the 2nd step of intramembranous ossification
- looks like a bone spicule*
- middle = ECM (bone matrix) with osteocytes (trapped osteoblasts)
- surrounded by cuboidal CT cells (not cuboidal epith):
- all that in environment full of mesenchymal cells
intramembranous ossification step 3: what happens after the initial spicule like bone formed + what is the end result of this step
- formation of secondary ossification centers similar to primary ones (groups of mes cells become osteoblasts)
- osteoblasts start growing perpendicular to the main spicule axis
- end result = trabecular bone bc of the perpendicular growth through all the bone*
what is also happening during the formation of trabecular bone (secondary ossif centers, step 3)
osteoclasts start to appear. multinucleated cells, incorporate in the osteoblasts (cuboidal CT cells) lining the bone matrix
- the bone is deposited and they remove some of it
- result = an addition and removal of bone happens in one specific orientation***
intramembranous ossification step 4: what is happening as/ happens after secondary ossif centers, trabecular bone formation occurs
mesenchymal cells surrounding the trabecular bone differentiate into periosteum
intramembranous ossification step 5: what happens after trabecular bone with periosteum is obtained
- ossification centers (primary and 2ndary) grow radially and fuse
- result = spongy bone called WOVEN BONE (seen in the fetus, collagen fibers disorganized, not lamellar)
intramembranous ossification step 6: what happens after you get woven bone with a periosteum
the periosteum (formed by the most external mesenchymal cells) forms a thin layer of compact bone surrounding the woven bone
architecture of the resulting woven bone in intramembranous ossification (with 2 things to note)
3D structure:
- trabecules of woven (immature bone)
- osteocytes in lacunae (within the bone matrix)
- osteoblasts on trabecules surface
- LOT OF LOOSE CT SURROUNDING THE TRABECULES
- periosteum on periphery surrounding the loose CT (there’s a lot of it) with the trabecules
- BLOOD VESSELS OCCUPY THE WOVEN BONE A LOT
what will the periosteum layer surrounding the woven bone (trabecules + loose CT) do (it came from mesenchymal cells)
will produce compact bone that replaces all woven bone
growth of the skull: direction of bone growth + location of bone formation and bone resorption
growht occurs outwards, expanding the brain
- bone formation on outside surface of the skull
- bone resorption on inside surface of the skull
what happens to the initial trabecules (surrounded by loose CT and a periosteum) formed by intramembranous ossif in the embryo and fetus
- the initial trabecules increase in size*
- apposition of new layers of woven bone (in embryo and fetus)
- some layers may fuse to form a larger plate
- on the plate surface, focal regions of activity appear which result in spicules of bone forming perpendicular to surface of original trabecule
in the growing woven trabecullar bone (skull bone for example), what occupies the spaces between adjacent trabecules or between trabecules and spicules (trabecules = part of surface. spicule = spiking perpendicular to the surface)
blood vessels and loose CT
forces acting on the bone determining which surface of a flat bone gets resorbed and which gets bone formation
- bone receiving pressure on one surface resorbs on that surface (inside surface of the skull, a flat bone, for example. it receives P of brain growing so bone being PUSHED)
- bone being tensed (having tension) on one surface will form bone on that surface (outside surface of the skull, a flat bone, for example. being PULLED)
how to recognize the primary ossification center in a woven trabecullar bone with many trabecules
is the largest trabecule, may appear central with trabecules of expanding woven bone that are less large, growing from it
in the growing woven trabecular bone with many ossif centers growing perpendicularly and making trabecular bone, what happens to periosteum on periphery eventually (formed by mes cells)
it will eventually become 2 layers. inner and outer. (inner is on one side of the bone, side of bone resorption, and outer is on other side, side of bone formation)
what woven trabecular bone with inner and outer periosteum will form in later life
woven bone disappears and replaced by contact lamellar bone
what is the reason for which bone receiving pressure resorbs and for which bone under tension forms bone
- osteoclasts sense the pressure and bone resorbs
- osteoblasts sense tension and add bone
bone transformation that can occur other than woven trabecullar nonlamellar bone becoming secondary bone (compact or spongy)
spongy bone (secondary, trabecullar, cancellous, regular fibers) can become compact bone (secondary, lamellar, regular fibers
endochondral ossification is for formation of what type of bone
short and long bones
initial thing needed for endochondral ossification
you need a piece of hyaline cartilage whose shape ressembles a small version of the bone to be formed (anlagen)
2nd step of endochondral ossification (after have anlagen)
perichondrium on periphery (area of diaphysis) transforms into periosteum and deposits bone, forming a bone collar (ribbon of bone present in the middle of the forming bone shaped structure)
steps of formation of a bone collar (how periosteum of anlagen forms a bone collar and becomes periosteum)
- becomes periosteum bc perichondrium transforms into periosteum
- periosteum has many pluripotential cells
- periosteum differentiates and produces different primary ossification centers and trabecular bone (it is INTRAMEMBRANOUS OSSIFICATION occurring in the periosteum)
next step of endochondral ossification: what is the consequence of the formation of the bone collar
- interferes with nutrition to the cartilage bc there are no blood vessels in hyaline cartilage
- the cartilage degenerates (3 steps): chondrocyte hypertrophy, chondrocyte death, ECM calcification (ECM calcifies everytime a chondrocyte dies)
appearance of forming endochondral bone with dying cartilage
- surface with trabecular bone + bone spicules + osteoblasts
- center with dying cartilage (becomes calcified. the ECM appears basophilic)
next step of endochondral ossification: what happens after ECM calcifies and cartilage dies
- blood vessels invade the calcified cartilage. the invasion is led by OSTEOCLASTS
- they come from the periosteum (the blood vessels and osteoclasts)
- occupy space where chondrocytes died
charact of blood vessels invading calcified ECM and dead cartilage in endochondral ossification
- carry many osteoprogenitor cells with them
- these will diff into osteoblasts
- osteoblasts attach to calcified cartilage
endochondral ossification: step after osteoblasts attaching to calcified matrix (cartilage)
- osteoblasts divide and secrete ECM
- this produces trabecules of primary woven bone (so 2nd place of trabecular bone formation (primary ossif centers) after the periosteum previously)
structure formed in the middle of the bone as a result of trabecular bone formation by osteoblasts in the calcified cartilage
zone of mixed spicules (called mixed bc have cartilage, bone and osteoblasts. in that order towards a blood vessel)
what’s a mixed spicule (found in growing endochondral bone)
structures that are parallel to bone length. spicule components are
- blood vessel in middle (parallel to bone axis)
- osteoblasts on each side of vessels
- bone formed by osteoblasts
- calcified cartilage in middle of each vessel-osteoblast-bone structure
in endochondral ossification, what happens after the long bone with mixed spicules is formed
secondary ossification follows, and it happens at the epiphysis of the future bone (no real epiphysis yet)
what happens in secondary ossification happening at epiphysis during endochondral ossification
similar to primary ossification centers
- cartilage degenerates and is invaded by blood vessels
- the blood vessels come from the perichondrium and carry perichondrium transformed in periosteum (so has osteoprogenitor cells)
- mixed spicules ( = WOVEN BONE) are formed
in secondary ossification at the epiphysis in endochondral ossification, where will cartilage remain
2 places
- at the articular surface
- at the epiphysial plate
shape of the epiphyseal plate
disc
in endochondral ossification, what happens after the formation of a diaphysis and an epiphysis regions with mixed spicules
- osteoclasts start being active
- they start chewing out the mixed spicule
- this is important to produce the marrow (the cavity)
endochondral ossification has a primary ossif center and a secondary ossif center: what happens to those as you age
- the centers will eventually fuse
- short term leaves a scar
- long term not visible and all appears as one thing bc blood vessels break through
different portion of bones
- epiphysis near end (where 2ndary ossif center is)
- epiphysial plate (hyaline cartilage)
- metaphysis
- mixed spicules
- diaphysis (where primary ossif center is)
special thing about the cartilage at the bone articular surface
it has no perichondrium so it’s difficult to repair if it’s torn
does the epiphysial plate have perichondrium with its cartilage?
yes, has a bit of perichondrium.
allows lateral growth of the epiphysial plate with age
growth of long bone is the result of what events
the development of the various parts of the bone in synchrony
growth of long bone: speed and steps as you age
- rapid during primary bone formation (embryo + fetus)
- continues in childhood and adolescence
- slows down in adulthood
- stops at some point in adulthood when secondary bone formation starts
growth of long bones: components of the growth plate (will induce the growth of the bone)
hyaline cartilage (with isogenous groups, lacuna, chondrocytes).
resting cartilage
-1 zone of cells like that, distal (closer to the epiphysis), with RESTING chondrocytes
-1 zone (THE PROLIFERATION ZONE) of cells like that, proximal (closer to diaphysis), with ACTIVE chondrocytes placed in stacks/columns of cells following bone axis
growth of long bones: what do the active chondrocytes do in the growth plate
- divide actively
- produce roads of chondrocytes
- called the proliferation zone*
growth of long bones: why do we say that bone grows inwards?
the cells proliferating in the growth plate are from the side facing the diaphysis. they divide and push the epiphysis away from the diaphysis.
it’s not cells forming on the epiphysis side
growth of long bones: what happens to chondrocytes being put in roads towards the diaphysis by the growth plate?
- form a zone of chondrocyte hypertrophy (below the zone of proliferation)
- the most distal chondrocytes (closest to diaphysis) die. you get a zone of cell death (below the zone of chondrocyte hypertrophy)
growth of long bones: what is happening in the zone of chondrocyte hypertrophy
- chondrocytes accumulate glycogen in their cytoplasm
- the resorbed ECM (bone matrix) is reduced to a thin septa which starts to calcify
growth of long bones: what happens in the zone of cell death below the growth plate
- a cavity is left open due to cell death
- blood vessels coming from the diaphysis (opposite side) invade this space. (so initially got through the periosteum and now get through the diaphysis)
- invade the dying chondrocytes (of zone of cell death) which forms a ZONE OF VASCULAR INVASION below the zone of cell death
growth of long bones: charact of the blood vessels invading zone of cell death and forming a zone of vascular invasion below it
are capillaries carrying osteoprogenitor cells
growth of long bones: what happens to the ECM when chondrocytes die in the zone of cell death
- it calcifies and it dies (no more chondrocytes)
- calcium phosphate deposits on the ECM
- it will serve as a substrate to which osteoprogenitor cells will attach
growth of long bones: what osteoprogenitor cells will do when come with vascular invasion
- attach to calcium phosphate in calcified, dead ECM of zone of cell death
- form osteoblasts and bone spicules (zone of mixed spicules, = vessel, osteoblast, bone (osteocytes from these osteoblasts), cartilage)
growth of long bones: appearance of mixed spicules being formed by invading osteoblasts
cuboidal cells lining around the matrix and producing bone (result = spicules)
the bone between cartilage and osteoblasts = osteocytes + matrix
growth of long bones: what can happen later to the zone of mixed spicules
can be eaten by osteoclasts (will be next step)
growth of long bones: summary of the layers of the epiphyseal plate
- resting zone
- zone of prolif
- zone of hypertrophy
- zone of cell death
- zone of vascular invasion
- zone of mixed spicules
growth of long bones: appearance of the resting zone of epiphyseal plate on histo
- isogenic groups typical of hyaline cartilage (chondrocytes)
- the chondrocytes are very active and do mitosis
- this mitosis forms isogenic groups that look like stacks and that arevery long
- cartilage is growing and pushing away from the diaphysis
growth of long bones: appearance of mixed spicules on histo
- lot of white zone with debris = blood vessels, invasion of osteoprogenitor cells
- osteoblasts lining spicules (or may appear as a big group meaning you have a face view)
- bone with osteocytes (acidophilic) on other side of osteoblasts
- calcified matrix with no cells (basophilic and pale) in middle of spicules
growth of long bones: what happens to the zone of mixed spicules
spicules are dissolved by the action of osteoclasts (multinucleated cells with a ruffled border looking like a brush border)
growth of long bones: origin of osteoclasts for the dissolution of mixed spicules
- hematopoietic precursor cells (NOT mesenchymal cells)
- RANKL activates the transformation of these to make osteoclasts
growth of long bones: how osteoclasts dissolve mixed spicules
- attach to mixed spicules and create a sealed compartment
- produce hydrolytic enzymes + protons (acidic environment)
- bone resorption occurs and calcium phosphate is removed
growth of long bones: end result of osteoclasts dissolving the calcified cartilage and the mixed spicules
- resorption of woven bone
- formation of a hollow marrow
growth of long bones: what regulates growth and long bones
various hormones acting at the epiphyseal plate
synovial joint: other name for the synovial joint
diarthrosis
synovial joint function
- joins two bones with a fibrous joint capsule that is continuous with the periosteum of the joined bones
- the capsule is the outer boundary of the synovial cavity and surrounds the bones’ articular surfaces
synovial joint: layers of the fibrous joint capsule in a synovial joint
- external fibrous layer
- internal synovial layer
- inside that = synovial cavity filled with synovial fluid*
synovial joint: what is found at the articular surface of a diarthrosis (synovial joint)
- hyaline cartilage with no perichondrium with chondrocytes arranged in vertical rows
- no blood vessels in hyaline cartilage
- note: the fibrous joint capsule of synovial joint is continuous with bone periOSTEUM*
synovial joint: content of the external fibrous layer of the fibrous joint capsule
- dense fibrous tissue
- abundant type 1 collagen
- this external fibrous layer can be called the FIBROUS CAPSULE*
synovial joint: content of the innermost portion of the joint capsule (internal synovial layer)
- synovial membrane (called the synovium). cells lining cavities + CT with vessels, cells, etc.
- more cellular
- leaky to fluids so allows extensive transfer of fluids (synovial fluid) to the joint space
- may be folded along with some of the underlying CT so it may project inside the joint cavity
synovial joint: diff names to the external layer of the capsule
- external fibrous capsule
- fibrous capsule
- external layer
synovial joint: diff names to the internal layer of the capsule
- synovial membrane
- synovium
- internal synovial layer
synovial joint: charact of the CT of the synovium
- highly vascularized
- contains large fenestrated leaky capillaries
synovial joint: cells in the synovium
- synoviocytes or type B cells (are modified fibroblasts) lining the synovial cavity
- some macrophages (type A cells) along the synoviocytes
synovial joint: different things the synovium touches
- deep on the bone, will touch the periosteum (below epiphysis)
- near the synovial joint, still on bone, will touch the perichondrium (on the epiphysis)
- in the synovial joint, touches synovial fluid
structure of the epiphysis of bone
- epiphysis in the middle
- calcified cartilage surrounding the half of the epiphysis that points to the synovial joint
- articular cartilage surrounding the whole epiphysis (and surrounding calcified cartilage for the portion of epiphysis covered by calcified cartilage)
synovial joint: why the synovium is not epithelium
- no gap junctions
- no junctional complexes
- no basement membrane
- discontinuous
the synovial cavity can be considered a _______
ECM.
-the permeable capillaries allow diffusion of fluid easily, which then traverse the modified fibrocytes (synoviocytes)
what happens to the folds of the synovium in the case of inflammation of the synovial cavity
the folds (synovium that folds into cavity with some of its underlying CT) will become swollen
on histology, what are the various spaces found in the synovial joint capsule (synovium + fibrous capsule)
blood vessels
