2.  Begins 6 weeks after fertilization  Continues throughout adolescence  Can continue until 25  Ossification—replacing tissue with bone

3.  Differentiate into bones  Flat bones form this way

5.  Most bones formed this way  Forms from hyaline cartilage models  Cartilage starts to calcify  Osteoblasts cover shaft  Blood vessels penetrate the cartilage  Bone of shaft thickens

7.  Women—stop by 18  Men—stop by 20

8.  Calcium  Comes from mom pre-birth  Mom loses bone mass while pregnant

9.  Vitamin D3  Through vitamins or UV rays  Processed by liver  Allows calcium and phosphate to be absorbed

10.  Rickets  Soft and bendable bones in kids  Result of vitamin D deficiency  Bowlegged appearance

12.  Vitamins A and C  Scurvy—lack of vitamin C  Decreased osteoblast activity  Weak and brittle bones