Bone 2 Flashcards
Intramembranous bone formation- when does it begin
When mesenchymal cells condense to
form a primary ossification center, from which
osteoblasts differentiate and begin secreting
osteoid
Intramembranous bone formation-Development of ossification center:
osteoblasts secrete organic extracellular
matrix
Intramembranous bone formation-Calcification:
calcium and other mineral salts
are deposited and extracellular matrix
calcifies (hardens)
intramembranous bone formation-Bone trabeculae (fused spicules)
Ossification centers expand into spicules as more
osteoblasts aggregate
and Bone trabeculae (fused spicules) is the name given to the
bone developing at these sites
Intramembranous bone formation-flat bones of the skull formation
-Blood vessels invade the area at the same time that undifferentiated
mesenchymal cells give rise to bone marrow cells
• Periosteum forms from surrounding mesenchymal cells
• Numerous ossification centers fuse together forming bone
the formation of trabeculae
Primary bone is initially produced. It is later replaced by mature secondary bone. As the spicules continue to grow, they fuse with adjacent spicules
10 steps of Endochondral bone formation
1) Outline of bone in hyaline cartilage
2) Formation of periosteum and subperiosteal bone
collar for support in diaphyseal region
3) Cartilage matrix is calcified
4) Blood vessels erode into calcified cartilage
5) Formation of periosteal bud consisting of osteogenic cells
and blood vessels (primary ossification center)
6) The subperiosteal collar becomes thicker and bone forms
on the calcified cartilage complexes
7,8) Secondary ossification centers (in a similar manner)
form in the epiphyses. Epiphyseal cartilage (epiphyseal
growth plate) is formed between the primary and
secondary ossification centers
9) Epiphyseal plate disappearance occurs at different times
10) Fusion of diaphyseal and epiphyseal marrow cavities
Endochondral bone formation – epiphyseal
plate;Zone of reserve cartilage:
cartilage with small,
randomly arranged inactive
chondrocytes. Serves as
stem cell line.
Endochondral bone formation – epiphyseal
plate;Zone of cell proliferation:
rapid mitotic divisions give
rise to rows of cartilage
cells
Endochondral bone formation – epiphyseal
plate;Zone of hypertrophy
the chondrocytes are greatly enlarged and the cartilage matrix between neighboring cells becomes thin.
Endochondral bone formation – epiphyseal
plate;Zone of calcified cartilage:
lacunae coalesce and the interlacunar
matrices become calcified, causing apoptosis of chondrocytes
Endochondral bone formation – epiphyseal
plate;Zone of resorption:
bone is beginning to be elaborated upon the
calcified cartilage, and osteolytic activity begins to resorb the calcified
bone-cartilage complex
Development of osteons
Longitudinal ridges form along the bone and osteogenic cells
in the periosteum transform into osteoblasts
• Osteoblast start producing bone matrix which form ridges
that close off periosteal capillaries as they meet
• Periosteum lining the newly formed canal becomes the
endosteum and starts forming concentric lamellae to form
the osteon
Bone repair
-Fractured bone results in damage to bone matrix -macrophages remove much of the debris via phagocytosis -Fibroblasts proliferate in the periosteum and endosteum and surround the area internally and externally to isolate it
Bone repair -Callus formation
-formed both internally and
externally
-Bone is elaborated in the fracture zone via
intramembranous bone formation by osteoblasts
Bone repair -Callus formation
-formed both internally and
externally
-Bone is elaborated in the fracture zone via
intramembranous bone formation by osteoblasts
Bone repair- how is bony callus composed of primary bone formed
-Chondrocytes also differentiate from this connective
tissue and elaborate cartilage, which will be replaced by
bone via endochondral bone formation, thus forming a
bony callus composed of primary bone
-Bony callus is eventually resorbed and replaced with
secondary bone as the repair process continues
Histophysiology- Bone
- Supports the body
- sites of attachment
- Protects the CNS and vital organs
- Dynamic tissue
Histophysiology-Calcium reserve
-Bone contains about 99% of the body’s calcium
-Decalcification of bone results from diet inadequate in
calcium
-remodeling-calcium is
transferred from the bone into the blood stream
bone development- Diets low in protein
result in
eficiency of amino acids essential for
collagen synthesis by osteoblasts
bone development-Lack of calcium
results in poorly calcified bone, which leads
to rickets in children and osteomalacia in adults
bone-Vitamin D is necessary for ?
ossification (excess
may actually cause bone resorption)
Bone -Vitamin A deficiency ?
inhibits proper bone formation and
growth (excess accelerates osteoclast activity and makes
bone fragile)
function of Parathyroid hormone (PTH) in bones and calcium
-indirectly stimulates osteoclasts to resorb and
release calcium, thus elevating blood calcium levels
-May activate osteocytes to initiate osteolysis ,
whereby they liberate calcium from the walls of their
lacunae, thus elevating blood calcium levels
function of Calcitonin in bones
Inhibits matrix resorption by osteoclast
and thus prevents the release of calcium
- lowers blood calcium levels
function of Pituitary growth hormone (GH) in in bones
Stimulates epiphyseal cartilage growth, so that an excess in childhood produces a giant, while a lack produces a dwarf • In adulthood excess GH results in acromegaly
Osteoporosis
Means ‘porous bone’ and result from progressive loss of
bone density leading to increased risk of fracture
Osteoporosis-Primary Type 1
In post-menopausal women estrogen levels decrease with menopause
Estrogen normally limits activity of osteoclasts
1/3 postmenopausal women affected (hormone therapy, selective estrogen
receptor modulators therapy available)
Osteoporosis-Primary Type 2
In elderly in their 70-80’s
Secondary osteoporosis
Develops as a consequence of drug therapy (corticosteroids) or other disease process (malnutrition, weightlessness, metastatic cancer, radiation)
Intramembranous ossification
- within condensation of
mesenchymal tissue.
Endochondral ossification
within a piece of hyaline
cartilage whose shape resembles a small model of
bone to be formed
