V. Bone Growth and Remodeling

A. The epiphyseal plate 1. Consists of 4 zones a. Zone of resting cartilage- small scattered chondrocytes that don’t participate in growth but anchor the plate to the bone b. Zone of proliferating cartilage- larger stacked chondrocytes that replace dieing ones at the diaphyseal face

c. Zone of hypertrophic cartilage- chondrocytes that cause a lengthening of the epiphyseal plate d. Zone of calcified cartilage- dead cells that have been surrounded by calcified cartilage and bone cells develop

2. Because of the activity in the epiphyseal plate, the diaphysis of a bone increases in length by interstitial growth 3. Bone grows in diameter by adding new bone tissue by the periosteal osteoblasts around the outer surface of bone

B. Remodeling 1. Remodeling is the ongoing process of replacing old bone tissue by new bone tissue 2. Old bone is constantly destroyed by osteoclasts where new bone is constructed b osteoblasts

a. Normal bone growth and remodeling are dependent on the presence of minerals 1. Calcium and phosphate are involved in bone matrix 2. Mg deficiency inhibits osteoblasts 3. Mn deficiency inhibits the laying of new bone 4. B keeps CA loss down and estrogen up

b. Vitamins D (holds Ca), C (matrix), A, and B12 (osteoblasts) are also important c. Hormones help bone activity 1. Human growth hormone 2. Sex hormones lay new bone