Bone formation
osteoclasts
a large multinucleate bone cell that absorbs bone tissue during growth and healing
growth in thickness
cooperative action of osteoblasts and osteoclasts
Zone of proliferating cartilage
-slightly larger chondrocytes are arranges in coins - interstitial growth as they divide and secrete extracellular matrix -chondrocytes in this zone divide to replace those that die at the diaphyseal side of the epiphyseal plate
step 3 growth in thickness
-Osteoblasts in the endosteum deposit bone extracellular matrix, forming new concentric lamellae. - -The formation of additional concentric lamellae proceeds inward toward the periosteal blood vessel. -In this way, the tunnel fills in, and a new osteon is created.
2 Hormones that Control Calcium
-Parathyroid Hormone (PTH) - when blood Ca to low, stimulates increase in osteocalsts and increases Ca uptake in small intestines -Calcitonin - secreated from thyroid when Ca levels to high which decreases osteoclast activity
benefits of remodeling bone
-Provides bone with continued strength -Regenerates Ca and P levels in blood -New bone is more resistant to fracture
step 3 Intramembranous Ossification
-bone extracellular matrix forms -develops into trabeculae that fuse to form spongy bone around network of blood vessels in tissue -
step 5 Endochondral Ossification
-branches of epiphyseal artery enter epiphyseal -spongy bone remains in the interior of the epiphyseal -proceeds outward from center of epiphysis -develop around time of birth
Zone of calcified cartilage
-cells thick and consists mostly of chondrocytes that are dead because the extracellular matrix around them has calcified osteoclasts dissolve the calcified cartilage -osteoblasts and capillaries from the diaphysis invade the area -osteoblast replaces the extracellular matrix with calcified cartilage -as a result the zone of calcified cartilage becomes new diaphysis that is firmly cemented to the rest of the diaphysis of the bone
step 2 Intramembranous Ossification
-secretion of osteoid stops -cells are called osteocytes -calcium and mineral salts deposited -> extrecellular matrix hardens/ calcifies
bone growth in length
-interstitial growth of cartilage on the epiphyseal side of the epiphyseal plate -replacement of cartilage on the diaphyseal side of the epiphyseal plate with bone by endochondral ossification
step 1 Intramembranous Ossification
-mesenchymal cells differentiate ->osteoblasts -osteoblasts secrete osteoid (bone matrix) -forming ossification center
step 4 growth in thickness
-osteon is forming -osteoblasts under the periosteum deposit new circumferential lamellae -further increasing the thickness of the bone -As additional periosteal blood vessels become enclosed as in step the growth process continues.
step 1 growth in thickness
-periosteal cells differentiate into osteoblasts, which secrete the collagen fibers that form bone extracellular matrix. -The osteoblasts develop into osteocytes -This process forms bone ridges on either side of a periosteal blood vessel. - The ridges slowly enlarge and create a groove for the periosteal blood vessel.
step 4 Endochondral Ossification
-primary center ossification grows toward ends of bone -osteoclasts break down spongy bone trabeculae -cavity forms in diaphysis - most of wall is replaced by compact bone
remodeling bone
-resorption:removal of minerals and collagen fibers by osteoclasts. -deposition: Addition of minerals and collagen fibers by osteoblasts
situations for bone growth
1. initial formation 2. growth 3. remodeling 4. repair fractures
Intramembranous Ossification
1. ossification center 2. classification 3. formation of trabeculae 4. development of periosteum
Calcium homeostasis
Calcium Homeostasis PTH indirectly stimulates osteoclasts ad releases Ca into blood. Calcitonin inhibits osteoclasts. Osteoblasts remove Ca from blood to make bone. In kidneys, PTH increases CA reabsorption from urine. In kidnesy, PTH also promotes formation of active Vit D which increases CA absorption from small intestines
repair of fracture
breaks in bones throughout life
step 2 Endochondral Ossification
chondroblasts-> chondrocytes growth occurs by cell division of chondrocytes
Zone of hypertrophic cartilage
consists of large, maturing chondrocytes arranged in columns
no stress weakens bones through
demineralization and collagen reduction
initial formation
formation of bones during embryology and fetal development
Second factor which controls bone growth and remodeling
gravity
growth
growth of bones during infancy, childhood and adolescence until adult size are reached
step 6 Endochondral Ossification
hyaline cartilage covering epiphysis -> articular cartilage length of bone grows
step 1 Endochondral Ossification
mesenchymal cells develop into chondroblasts -forming hyaline catrilage
step 4 Intramembranous Ossification
mesenchyme condenses at the periphery of bone and develops into periosteum -thin layer of compact bone replaces surface layer of spongy bone -spongy bone remains in center -newly formed bone is remodeled
zone of resting cartilage
nearest to epiphysis -small scattered chondrocytes -cells don't function in bone growth -anchor the epiphyseal plate to the epiphysis of the bone
Ecersise increases calcitonin which inhibits
osteoclasts and bone resorption
step 3 Endochondral Ossification
primary ossification inward from the external surface of bone -nutrient artery penetrates the perichondrium and the calcifying cartilage model through a nutrient foramen in the midregion of the cartilage model -bone tissue has replaced most of cartilage
Endochondral Ossification
replacement of cartilage by bone 1. development of cartilage model 2. growth of cartilage model 3. development of primary ossification center 4. development of the medullary cavity (marrow) 5. development of second ossification center 6. formation of articular cartilage and epiphyseal plate
remodeling
replacement of old bone by new tissue throughout life
step 2 growth in thickness
ridges fold together and fuse, and the groove becomes a tunnel that encloses the blood vessel -The former periosteum now becomes the endosteum that lines the tunnel.