Growth in the length of long bones.

• Interstitial Growth: Lengthens
• Appositional Growth - changes thickness

• Growth in length: Cartilage continually grows and is replaced by bone
• Modeling: Modeling occurs as bone grows into its mature form, it is the change in shape of the bone. Bone is resorbed and added by appositional growth. 
• Remodeling: The constant turnover of bone, shape does not change (unless resorbtion to point of fracture like crush factures in vertebrae). This is done by osteoblassts and osteoclasts throughout life in response to changes in the bone microenvironment.

• Growth zones: Where cartilage cells undergo mitosis, pushing the epiphysis away from the diaphysis
• Transformation Zone: Where older cells enlarge, the matrix becomes calcified, cartilage cells die, and the matrix begisn to deteriorate.
• Osteogenic zone: Where new bone formation occurs

• Zone of resting (quiescent) cartilage: Chondrocytes anchor epiphyseal plate to the epiphysis of the bone.
• Zone of growth/Proliferation Zone: Chondrocytes are arranged in stacks of coins, slightly enlarged.
• Zone of hypertrophic cartilage - Much larger maturing chondrocytes
• Zone of calcification - Calcification occurs in surrroundign matrix so chondrocytes are dead. Osteoclasts dissolve calcified cartilage and osteoblasts lay down.
• Zone of ossification - New bone is mineralized
• Once longitudeinal growth stops and the bone fuses, the area is referred to as an epiphyseal line.