Anatomy Lecture 7 Bone Formation

Front 1

What is intramembranous ossification?

Back 1

Bone forms directly from embryonic membranes. Forms non-weight-bearing bones. (Flatbones of skull)

Front 2

What is endochondral bone formation?

Back 2

Bone forms indirectly from cartilaginous templates. Most bones in the body are formed by endochondral ossification. (Long bones). Bone forms from hyaline cartilage.

Front 3

Steps of intramembranous ossification

Back 3

1.)Embryonic mesenchymal cells condense into a connective tissue membrane with increased vascularization 2.) Osteoblasts differentiate from the mesenchymal cells. Osteoid secretion forms spicules of pre-bone. Cells become attached by cytoplasmic processes. 3.) Calcium phosphate salts are deposited into the osteoid matrix. Osteoblasts become trapped in own matrix becoming osteocytes. 4.)Bone spicules continue to develop forming spaces with bone marrow and vessels. Inner and outer table is formed through compaction. 5.)Spongy bone core of flat bone retains trabecular appearance and remodeling is continual by osteoclasts and osteoblasts.

Front 4

Steps of endochondral ossification

Back 4

1.) Hyaline cartilage forms tiny template of future bone. 2.) Calcification of perichondrium precedes destruction of cartilaginous tissue. Bone collar forms on cartilaginous template in the region of the diaphysis (shaft of bone). 3.)Mineralization of hyaline cartilage template. Chondrocytes enlarge and are vacuolated. Lacunae enlarge, loss of matrix. Remaining cartilage is calicified through deposition of calcium phosphate. Chondrocytes begin to die, perichondrium becomes periosteum. 4.) Invasion of blood vessels. Chondrocytes die, osteogenic cells invade. periosteal bud invades internal calcified cartilage. 5.)Formation of primary center of ossification. Osteoblasts form new bone. New osteoid is deposited. Primary immature bone lacks osteons.6.)Formation of secondary centers of ossification-develop in epiphysis(ends of bone) postnatally. Similar to primary center but develops slower. Growth occurs in all directions forming an epiphyseal plate between primary and secondary centers. Eventually plate erodes and centers fuse. the epiphyseal line on the bone surface is the only remaining evidence of the plate.

Front 5

Bone Growth: Long Bones

Back 5

Endochondral ossification. Continued production of cartilage at the epiphyseal plate in metaphysis causes elongation. Growth by appositional growth(width) under periosteum. Bone collar grows in thickness due to layer-by-layer deposition of new bone.

Front 6

Bone remodeling

Back 6

Removal of osteoclasts(resorption) and redeposition by osteoblasts is required for eventual formation of size and shape of adult bone. Spongy bone: every 2 to 4 years. Compact Bone: every 10 years.

Front 7

Growth of Long Bones

Back 7

Occurs in metaphysis(lower end of epiphyseal plate).

Front 8

Zone of quiescence(reserve cartilage)

Back 8

Furthest from ossification center. Little growth

Front 9

Zone of proliferation

Back 9

Chondroblasts proliferate here causing active growth in length towards quiescent zone.

Front 10

Zone of maturation

Back 10

Cell division stops. Cells and lacunae enlarge. Further growth in length

Front 11

Zone of hypertrophy and calcification

Back 11

Chondrocytes greatly enlarge. Matrix becomes calcified

Front 12

Zone of degeneration

Back 12

Chondrocytes regenerate, matrix dissolves, lacunae breakdown, blood vessels invade with osteogenic cells

Front 13

Zone of resorption

Back 13

Osteoblasts surround calcified cartilage. Osteoid material is deposited on surface forming spongy bone trabecule with calcified cartilage center. Osteoclasts resorb bone. Marrow cavity enlarges.

Front 14

Termination of Bone growth

Back 14

Hormonal control of cartilage production at epiphyseal plate stops. Once plate stops producing new cartilage cells by proliferation, mineralization from primary center moves up plate and calcifies it. Once cartilaginous plate is calcified, it in turn is resorbed by osteoclasts. Erosion of both plates result in fusion of 3 centers of ossification into a confluent marrow cavity. growth stops at this point

Front 15

Gonadal (sex) hormones

Back 15

precocious sexual development causes accelerated skeletal maturation and results in short stature.

Front 16

Growth hormones

Back 16

Growth of bone is regulated by anterior pituitary.

Front 17

Hypersecretion

Back 17

Results in accelerated bone growth.

Front 18

Hyposecretion

Back 18

Causes shortness of stature

Front 19

Bone repair

Back 19

Repair after a fracture follows a similar pattern as to when it was formed.

Front 20

Callus Formation

Back 20

At fracture site, composed of clotted blood. Replaced by connective tissue and cartilage. The cartilaginous plug is replaced by bone via endochondral ossification. Takes 6-8 for process and healing. Repair leaves external callus.