Bone II Flashcards
Which parts of cortical bone have osteoprogenitor cells?
Periosteum and endosteum
What connects the periosteum to bone?
Sharpey’s fibers
What are canaliculi and what functions do they perform
They are channels that connect the lacunae in osteons essentially allowing exchanges
between osteocytes and blood capillaries. Cellular processes go through the canaliculi
and there’s diffusion of nutrients and O2 within them.
In compact bone, where do external circumferential and inner circumferential lamellae
reside?
Inner are located around the marrow cavity and external are located immediately
beneath the periosteum
Describe bone remodeling in cortical bone.
Osteoclasts remove old bone in tunnel-like cavities having the approximate diameter
of new osteons. Such tunnels are quickly invaded by many osteoprogenitor cells and
sprouting loops of blood capillaries. Osteoblasts develop, line the walls of the tunnels,
and begin to secrete osteoid in a cyclic manner, forming concentric lamellae of bone with
trapped osteocytes. They use the blood vessel as a guide.
What are interstitial lamellae? How do they form?
When new generations of Haversion systems form they form progressively, and the remodeled remains (fragments) left over become interstitial lamellae.
What is the newest lamella of each Haversian system?
The newest is the innermost layer of the Haversion system because successive
deposition of lamellae start from the periphery and proceed inward. As osteoclasts drill
open the old bone, osteoprogenitor cells in the reversal zone differentiate into osteoblasts
that form onion-like layers from the outside in.
What cells are found in lacunae?
osteocytes
Compare/contrast periosteum and endosteum
Periosteum covers the external surface of bone; it’s dense irregular connective tissue.
The innermost cellular layer contains stem cells called osteoprogenitor cells that have the
potential to differentiate into osteoblasts. Endosteum lines the marrow cavity, lumen of
Haversion/Volkmann’s canals, outer layer of trabecular bones and also contains
osteoprogenitor cells and osteoblasts. Endosteum is loose irregular connective tissue.
The principle functions of periosteum and endosteum are nutrition of osseous tissue and
continuous supply of new osteoblasts for repair or growth of bone.
Do osteoclasts have one or several nuclei
they have several
What type of ossification occurs in flat bones?
intramembranous—evolves from a mesenchymal membrane
What type of ossification occurs in long bones?
A: endochondral ossification. The matrix of preexisting hyaline cartilage is eroded and
replaced by osteoblasts producing osteoid.
Discuss intramembraneous ossification. What type of bone does it occur in?
A: Occurs in most flat bones like frontal, parietal, occipital, maxilla, and mandible. It is
initiated in a membrane of mesenchyme where the cells condense and come together and
differentiate to osteoprogenitor cells and then osteoblasts. Osteoblasts produce osteoid
matrix and calcification follows, resulting in the encapsulation of some osteoblasts which
then become osteocytes. “Islands” of developing bone emerge and are termed primary
ossification centers or “bone blastema”. Several centers develop simultaneously and then
fuse together. When they fuse together they form a spongy network called “primary
spongiosa”. These thicken via appositional growth. So essentially, intramembranous
ossification is a process that initiates in a membrane that contains mesenchyme cells.
Discuss endochondral ossification. Where does it predominantly occur? What are the
two basic phases? Where do secondary ossification centers take place?
Takes place within a piece of hyaline cartilage whose shape resembles a small version
of the bone to be formed. It’s the type of ossification responsible for the formation of
short and long bones. Initially the first bone tissue appears as a collar surrounding the
diaphysis of the cartilage model (called the bone collar)—this collar is produced by
osteoblast activity within the surrounding perichondrium. The collar impedes diffusion
of oxygen and nutrients into the underlying cartilage, promoting degeneration. The
chondrocytes begin to swell up (hypertrophy). These changes compress the matrix into
narrower trabeculae and lead to ossification. Death of the chondrocytes results in a
porous 3D structure formed by the remnants of the calcified cartilage matrix. There’s
now an invasion of the open chamber by osteogrogenitor cells which then become
osteoblasts allow new bone (primary) to be laid down on top of the calcified cartilage
matrix. In other words, an “osteogenic bud” composed of osteoprogenitor cells and a
developing blood vessel drill through the boney collar and invade the open spaces and
thus form a “primary ossification center” midshaft. Osteoprogenitor cells are now in
place on top of calcified cartilage and they synthesize and lay down new (woven,
primary) bone by appositional growth on top of the calcified cartilage. A secondary
ossification center happens (same) in the epiphysis regions
What type of cartilage is responsible for the growth in length of the bone and
disappears in adults?
epiphyseal cartilage
