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.