7.3 Flashcards
ossification
process by which bones form
what happens at 6 weeks of ossification
skeletal framework is laid out
What happens at 8 weeks of ossification
bone cells begin to form bone tissue in the embryo
What do the two types of ossification have in common
*Both mechanisms involve the replacement of pre-existing connective tissue w/ bone
*Both kinds do not lead to differences in the gross structure of bones
Intramembrane ossification
*Bones originate w/ sheet-like layers of fibrous connective tissues
*Brood, flat bones (skull bones except mandible)
*Called intramembranous bones
Endochondral ossification
*Bones begin as hyaline cartilage and form models for future bones
*Called endochondral bones
*most bones of the skeleton
What is the process of intramembranous ossification?
*Layers of unspecialized fibrous connective tissues appear at sites of future bones
*Connective tissue forms around dense laters of blood vessels
*connective tissues cells differentiate into osteoblasts
-deposit bone matrix around themselves
-spongy bone forms in all directions around blood vessels
-can become compact bone later
*once completely surrounded by matrix osteoblasts become osteocytes
*cells outside of the developing bone give rise to periosteum
*Osteoblasts on the inside of the periosteum begin to develop into a layer of compact bone
Endochondral ossification
*Masses of hyaline cartilage form a model of future bone
-Cartilage matrix begins to break down and cartilage cells (chondrocytes) begin to die
*connective tissue encircling structure begins to form periosteum as cartilage decomposes
*Blood vessels and osteoblasts invade decomposing tissue from the periosteum
*Osteoblasts begin to form spongy bone in the spaces occupied by cartilage
-once completely surrounded become osteocytes
*Osteoblasts beneath the periosteum deposit compact bone around the spongy bone
Long bones formation
*Bony tissue begins to replace hyaline cartilage in the middle of the diaphysis= primary ossification center
*Epiphyses remain cartilage and continue to grow while diaphysis becomes bone
-compact bone forms around the periosteum
*secondary ossification centers develop in the epiphysis
-spongy bone forms in all directions
*As these two centers develop, a band of cartilage remains between these two centers called the epiphyseal plates
Epiphyseal Plate
*made of 4 layers of cartilage cells
First layer of epiphyseal Plate
-closest to ephiphyses
-resting cells closest to the ephipyses
-anchors epiphyseal plate to bony tissue in epiphyses
Second layer of epiphyseal Plate
-many rows of younger cells undergoing mitosis
-Thickens the cartilage plate
Third layer of epiphyseal Plate
-old cells left behind when new cells form
-enlarge the plate even more, causing bone lengthening
-also beginning to calcify ,cartilage cells die
Interstitial growth
hpattern of growth resulting in an increase in length -> cartilage cells (16-25)
Appositional growth
osteoblasts deposit layers of matrix on the surface of bone -> growth in diameter (45-50)
