Bone formation, known as ossification, begins after eight weeks of fetal development, primarily through endochondral ossification of hyaline cartilage. Long bone growth occurs through the activities of osteoblasts and osteoclasts, with epiphyseal plates facilitating length increase. Several factors, including genetics, minerals, vitamins, hormones, and mechanical stresses, influence normal bone growth and health.

1. Unit 4: The Skeleton System
Section 3: Bone Formation & Growth
Anatomy & Physiology
Mrs. DeFord

2. Ossification is the process of bone formation. It
occurs after the 8th week of fetal development.
• Most bones of the skeleton are formed through
endochondral ossification of existing hyaline
cartilage.
– Long bones: three ossification centers (at each
end and in the middle); ossification occurs from
each end toward the center and from the center
towards each end
– Short bones: one ossification center in middle
and proceeds towards ends of bone
Ossification

3. Long Bone Development

4. Two growth processes are responsible for long bone development.
First Process:
• OSTEOBLASTS (bone builders) – add bone to the outside surface,
enlarging and elongating the bone.
• OSTEOCLASTS (bone eaters) – tunnel out the marrow cavity and internal
spaces (these work at the same time as osteoblasts.)
Second Process (greatest growth):
• EPIPHYSEAL PLATES (growth plates) are found at either end of the bone
where the shaft (diaphysis) meets the head or base (epiphysis). These
growth plates are made of cartilage cells which multiply rapidly and the
outside cells ossify, increasing the length of the shaft.
Bone Growth of the Long Bone

5. Short Bone Growth

6. Human Body Bone Growth Pattern
• The human body changes length in the following pattern:
– Feet and hands develop first (increase in size)
– Lower legs and forearms grow rapidly
– Thighs and upper arms increase in length
– Finally, the trunk develops in length
• The width of the body develops next, as the shoulders and pelvis widen

7. • Minerals:
– Calcium and Phosphate (increases bone density)
• Vitamins:
– Vitamin D3 (promotes bone resorption)
– Vitamin C (required for collagen synthesis and stimulation of osteoblast
differentiation)
– Vitamin A (stimulates osteoblast activity)
• Hormones:
– Growth Hormone (stimulate bone growth)
– Sex Hormones (stimulate osteoblasts, responsible for gender differences in
skeleton)
– Thyroid Hormones (stimulates replacement of cartilage by bone)
Requirements for Normal Bone Growth

8. • Basic control of growth is genetic.
• Bones change in shape throughout life. This remodelling occurs in
response to:
– Hormones (mentioned previously)
– Mechanical stresses acting on the skeleton:
• Starvation and malnutrition can delay growth spurt.
• Major illness slow down growth.
• Regular exercise has many growth benefits.
• Aerobic exercise also increases the size and efficiency of the heart,
blood and lungs. However, repetitive long distance training for
marathons or triathlons may damage epiphyseal plates.
Factors Affecting Growth