Bones and their Growth Study Guide

Bone formation discusses the process of ossification and how bone is formed.

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  • Normal bone formation and growth is dependent on an adequate intake of nutrients. Bone development starts from conception and continues until early adulthood or in the early 20s.
  • The growth of the bones stops but continues increasing in density and mass by mineralization to build strength and flexibility.
  • The formation of new bone cells repairs the old bones until old age through the slow process of new bone formation.

Process of Bone Growth:

The formation of bone is often referred to as either ossification or osteogenesis. There are two types of ossification: intramembranous and endochondral ossification.

- Intramembranous ossification is the formation of bones in place of connective tissues.

  • Flat bones and irregular bones are formed through this process of bone formation.
  • When hyaline cartilage is replaced with bone tissue, this process of bone formation is called endochondral ossification.
  • Almost all of the bones in the skeletal system are formed through this process, and this is when the first bones are formed during baby formation.
  • The formation of endochondral bones happens in five stages.

- Endochondral ossification begins with forming a primary ossification center at the hyaline cartilage, where the hyaline cartilage serves as the template for the formation of the bone.

  • The blood vessels penetrate and flourish these cells that grow, resulting in secondary ossification centers.

Bone growth is either longitudinal or appositional.

  • Longitudinal bone growth is the ossification of the bone that grows lengthwise until they stop growing.

  • Appositional bone growth continues till death and is the growth of the bones in diameter or thickness. In appositional bone growth, the bones are formed in the outer external surface while the old inner bones break down.

The process of ossification results in the formation of three types of bone cells: osteoblasts, osteocytes, and osteoclasts.

  • Osteoblasts help in the formation of the bones
  • Osteocytes are the mature bone cells
  • Osteoclasts are the cells that help in the repair or remodeling of the bone cells and bone resorption.


  • Adequate intake of vitamin D and calcium-rich foods are needed for healthy and strong bone formation.
  • Bones also need other minerals like phosphorus and magnesium. Bone formation is a replacement process.


1. What are the 5 stages of bone growth?

  • Mesenchymal cells differentiate to form the chondrocytes resulting in a cartilage model, which is then flushed with blood vessels.
  • The blood vessels enter the cartilage deeper as capillaries to form the primary ossification center.
  • The cartilage and chondrocytes expand to form the medullary cavity, thereby paving the way for remodeling.
  • Finally, the zones of ossification are formed, resulting in the development of bone.

2. What are the three types of bone growth?

Osteoblasts, osteocytes, and osteoclasts are the three types of bone cells formed during different bone growth stages.

3. Which bones grow the most?

Long bones keep growing since birth. During adolescence, when there is maximum bone growth, the long bones of the legs and arms and the nose grow the fastest.

4. How does bone grow and develop?

The bone grows and develops through the process of osteogenesis or ossification.

5. What are bones made of?

Bones are made of protein collagen that forms the skeleton of the bone, which gets strengthened and hardened with the deposition of the mineral calcium phosphate.

6. What are the two types of bone development?

The two types of bone development are intramembranous and endochondral ossification.

7. Why do bones stop growing?

Bones stop growing during early adulthood because of maturation, but the bone mass increases until the late twenties.

8. What is longitudinal bone growth?

The epiphyseal plate is the region where longitudinal growth occurs, increasing the length of the bone.

9. How do bones grow and change with age?

Bones keep growing with age until full growth is reached, after which the bone builds mass and density. The bone later keeps repairing itself to remain new and strong until old age, when this process slows down drastically.

10. What is the appositional growth of cartilage?

Appositional growth is the growth of the bone across the diameter, and the bones grow on their surface.

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  1. Osteogenesis: The Development of Bones. https://www.ncbi.nlm.nih.gov/books/NBK10056/#:~:text=There%20are%20two%20major%20modes,the%20bones%20of%20the%20skull. Accessed Nov 26, 2021.
  2. Bone Development & Growth. https://training.seer.cancer.gov/anatomy/skeletal/growth.html. Accessed Nov 26, 2021.
  3. Bone Growth. https://flexbooks.ck12.org/cbook/ck-12-biology-flexbook-2.0/section/13.5/primary/lesson/growth-and-development-of-bones-bio/. Accessed Nov 26, 2021.
  4. Bone Formation and Development. https://open.oregonstate.education/aandp/chapter/6-4-bone-formation-and-development/. Accessed Nov 26, 2021.