Musculoskeletal Flashcards
choose the option that is correct:
Osteoclasts:
-are found in the resting endosteum and periosteum
-secrete their enzymes into an acidic environment in order to activate them
-are less common on trabeculae due to the reduced surface area
-remove hydroxyapatite by secreting enzymes
-use the clear zone to keep the destructive elements that they secret out of their Howship’s lacunae
secrete their enzymes into an acidic environment in order to activate them
where are most long bones found?
Appendicular skeletone
what are the functions of the appendicular skeleton?
-movement
- fat storage(yellow)
how many bones are there in the axial skeleton?
80( some paired)
how many bones are there in the appendicular skeleton?
126(paired)
what are the functions of the axial skeleton?
support/protection
Haemopoises( red bone marrow)
what is the bone marrow at birth?
ALL red
how is bone count reduced throughout a lifetime?
during puberty, some bones fuse
elderly- even more bones fuse
what is the organization of a long bone?
width of the compact bone in epiphysis compared to the diaphysis
compact bone is thinner
in epiphysis( ~ 1 mm)
compression force between 2 bones allows a thin layer of compact bone if supported by trabecular from below
is there periosteum in the epiphysis?
No as in contact with another bone
instead have a tougher layer of articulate cartilage
what are the forces acting on the epiphysis of the fema?
compression and tension
where is endosteum found in the spongy bone?
covers the trabeculae
organisation of epiphysis
more spongy bone
organisation of diaphysis
cylinder shape, hollow( medullary cavity with bone marrow). Lightweight
what is the function of perforating (Sharpey’s) fibers
forms strong unions between structures outside the bone to the bone
Big where tendons and ligaments attach to the bone
what is the size of the compact/cortical bone in the diaphysis?
~1 cm
thick to withstand parallel forces
what types of fibers are in the bone ECM?
collagen fibres type 1 and 5
what types of fibers are in the bone ECM?
collagen fibers type 1 and 5
what is the function of collagen fibers in bone?
resist tension( stretching/pulling)
what does the ground substance in the bone contain?
hydroxyapatite
Ca10(PO4)6OH2
what is the function of the ground substance in bone?
resists compression (squeezing/crushing)
what type of cells are in the bone?
osteogenic
osteoblast
osteocyte
osteoclasts
overall what force does the bone resists?
tension+ compression= torsion
where are osteogenic cells located?
the surface of the bone in the periosteum and endosteum. Also inside central canals of compact bone
the function of osteogenic cells
normally dormant, but can divide and supply developing bine with bone-forming cells
the function of osteogenic cells
normally dormant, but can divide and supply developing bine with bone-forming cells
where are osteoblasts located?
usually in the layer under the peri or endosteum, wherever new bone is being formed
function of osteoblasts
synthesis, deposition and calcification of osteoid
put down new bone
when is the layer active?
when osteoblasts are present
what is osteoid?
- The organic extracellular matrix (mainly collagen) of bone, synthesized by osteoblasts prior to mineral deposition.
- Osteoid is 70% collagen with the remainder consisting of proteoglycans, other proteins and water.
what is calcification?
- This precursor matrix(osteoid) is eventually infiltrated with bone salts (hydroxyapatite) and this process is called calcification.
- This makes the bone strong but also dense, thus nutritive fluids cannot diffuse freely through it
how rapid is calcification?
can calcify an osteoid 70-80% in the 1st 3 weeks
after the initial 3 weeks can take years to fully calcify the bone
what is osteocyte and where is it located?
An osteoblast trapped within
lacunae inside the bone.
Osteocytes can
communicate with
neighboring cells
through their long
cellular processes
inside canaliculi
function of osteocytes
Bone tissue
maintenance
- live lattice inside the bone.
- localized minor repair
- Rapid Ca exchange
osteoclast
Fusion of
monocyte
(White Blood Cell)
progenitor
cells.
osteoclast function
Secretes acid and
enzymes.
Dissolves the
mineral and organic
components of
bone.
how long do osteoclasts live for?
2-3 months before self-destruction
what are the steps in osteoclast function?
1st: Dissolve
2nd: Endocytpse the dissolved products
3rd: Neutralise
4th: Exocytose the products out of the top of the cell
what is the process by which bone grows?
Appositional growth
Bone is too rigid to grow by a process called interstitial growth
describe the process of appositional growth
do bones spend more time in the active or resting state?
resting
what are these cells?
osteoblasts
what are these cells?
osteocytes
what are these cells?
osteogenic cells
Rickets
Not enough Ca2+ in the diet-> bone stays softer for longer. Osteoblasts keep laying down osteoid but do not calcify it
-when the bones get calcified they’re deformed
Not enough minerals & nutrients to produce Vit D. Need Vit D to absorb Ca2+ through the intestinal wall
osteomalacia
adults have formed but softer bones. Vit D defficiency
how do osteocytes contribute to regulation of Ca2+ and Phosphorus lvls?
osteocytes can pull Ca2+ and Phosphorus from the wall of the lacunae or add to the wall of the lacunae. Happens rapidly due to canniculi
why are canaliculi positioned in the same direction?
when laying down canaliculi cannot be pushed into existing calcified bone, can only push in the direction the bone is growing.
name the tissue/cell
layer of osteoid that has not been calcified yet
mostly collagen and proteoglycan
how do bones grow in length?
by the process called Endochondral ossification
Between epiphysis and metaphysis, there is a layer of hyaline cartilage called an epiphyseal/ growth plate.
Chondrocytes in the cartilage can divide and secrete more ECM, making the plate thicker-> pushes epiphysis away from the rest of the bone
The cartilage dies & gets used as a surface to put down new bone. Cartilage is replaced with bone.
Eventually, the rate of cartilage growth drops below the rate at which it is replaced with bone
-> Epiphysis and metaphysis fuse
how does the rate of bone growth and reabsorption change throughout your lifetime?
children: more growth than absorption
20-35: rate of growth and absorption are ~ the same
over 35: more absorption than growth. Bones become more fragile.
by what age are all immature bones replaced with mature?
3 yo
immature bone(woven) structure
collagen fibers inside are wavy, randomly arranged, and not so densely packed( neither are cells or ECM)
not as strong
how are collagen fibers laid down in mature/lamellar bone?
As osteoblasts deposit new bone onto a surface (appositional growth),
they do so in layers or sheets (lamellae). The collagen fibres are typically
put down in the same direction within a layer, but can alternate up to 90o
out of phase between the layers. This enables bone to withstand forces
from different directions, making it significantly stronger
what are the 2 types of lamellar( mature) bone?
spongy and compact bone
why can trabeculae not be bigger than 0.4 mm in the narrowest dimension?
an osteocyte should be within 0.2 mm away from the blood vessel
how is collagen layed in the osteon>
layers of alternating collagen between lamellae
how thick is compact bone?
normally > 0.4 mm
what is the process that forms primary osteons?
appositional growth
primary osteons are formed around existing blood vessels on the surface of the bone( normally in the periosteum)
Bone on either side of the blood vessel grows quickly but slow underneath-> forms crests that fuse to form a tunnel surrounding the blood vessel.
Periosteum layer becomes endosteum
The osteoblasts in the endosteum build lamellae inward filling the tunnel
how are secondary osteons formed?
by osteoclast activity
secondary osteons are created inside the existing bone
what triggers secondary osteon formation?
osteocytes die from the insufficient blood supply or there is microdamage in the bone
->chemical signals are released-> monocyte progenitor cells sense the signals and exit the blood vessels and fuse to form the osteoclasts
what is the group of osteoclasts that bore through the bone called?
cutting cone
what is the orientation of the 2ndary osteon formation?
the tunnel is oriented along the lines of greater stress through the bone( parts that get damaged more often)
how fast does the tunnel of 2ndary osteon progress?
~1mm every 20 days
how is the blood supply to the new 2ndary osteon layed?
a blood vessel grows into the tunnel that is being created.
how is the new endosteum formed in the 2ndary osteon?
After the tunnel has been created osteogenic cells move in, which differentiate into osteoblasts-> forms new Endosteum-> new lamellae are laid from inside of the tunnel towards the centre.
blood vessel grows in to supply the cells
what is the part of the new 2ndary osteon that grows lamellae inwards?
closing zone
what happens after the 2ndary osteon tunnel is reduced to the typical harvesian canal size?
osteoblasts can either die or become bone lining cells ( osteogenic cells) and contribute to the resting endosteum
where does most of the appositional growth happen when forming osteons?
at endosteum
are there osteons in spongy bone?
no
what is the “cement line”?
a line at the junction between the outermost lamella of the new osteon and the preexisting older bone
what bone is this?(spongy or compact)
spongy bone
no osteons
what bone is this?(spongy or compact)
compact
osteons present
what is this part of the bone?
circumferential lamellae
what happens to osteon with age?
harden
