Changes

==Endochondrial Ossification==

==Endochondrial Ossification==

*''Bone formation via cartilage.''

*''[[Bones and Cartilage - Anatomy & Physiology#Types of Bone|Bone]] formation via [[Bones and Cartilage - Anatomy & Physiology#Structure and Function of Cartilage|cartilage]].''

#Proliferating limb mesenchyme condenses.

#Proliferating limb mesenchyme condenses.

#The increased cell density triggers mesenchymal cells to differentiate into chondrocytes. Proliferation continues.

#The increased cell density triggers mesenchymal cells to differentiate into chondrocytes. Proliferation continues.

#The bone shape is formed, with a diaphysis (shaft) and epiphysis (bulbous ends).

#The bone shape is formed, with a diaphysis (shaft) and epiphysis (bulbous ends).

#Chondrocytes in the middle of the diaphysis stop proliferating and undergo '''hypertrophy'''.

#Chondrocytes in the middle of the diaphysis stop proliferating and undergo '''hypertrophy'''.

#*''The shaft is surrounded by the '''perichondrium''', a restrictive membrane. This means that the bone can only grow in length, not width. The epiphysis are pushed away from each other.''

#*''The shaft is surrounded by the '''perichondrium''', a restrictive membrane. This means that the bone can only grow in length, not width. The epiphyses are pushed away from each other.''

#After chondrocytes have undergone hypertrophy, they die.

#After chondrocytes have undergone hypertrophy, they die.

#*'''Osteoblasts''' on the inner side of the perichondrium invade the cartilage matrix.

#*'''Osteoblasts''' on the inner side of the perichondrium invade the cartilage matrix.

#*They then secrete the extra - cellular matrix characteristic of bone.

#*They then secrete the extra - cellular matrix characteristic of bone.

#*''Ossification occurs from the outside - in. This is called primary ossification, or perichondrial ossification.''

#*''Ossification occurs from the outside - in. This is called primary ossification, or perichondrial ossification.''

#Blood vessels invade the central region of the diaphysis to transport bone marrow stem cells and osteoclasts.

#Blood vessels invade the central region of the diaphysis to transport [[Bone Marrow - Anatomy & Physiology|bone marrow]] stem cells and osteoclasts.

#*The osteoclasts break down the cartilage matrix to allow room for the bone marrow.

#*The osteoclasts break down the cartilage matrix to allow room for the bone marrow.

#There is no perichondrium surrounding the eiphysis.

#There is no perichondrium surrounding the eiphysis.