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How do Bones Grow?

Alexandrea Dillon, Betsy Chesnutt
  • Author
    Alexandrea Dillon

    Alexandrea has taught secondary science for over six years. She has a bachelors degree in Teaching Secondary Science and a Masters of Education in Instructional Design. She's TESOL certified and a National Geographic Certified Educator. In addition, she was the spotlight educator for National Geographic in late 2019.

  • Instructor
    Betsy Chesnutt

    Betsy has a Ph.D. in biomedical engineering from the University of Memphis, M.S. from the University of Virginia, and B.S. from Mississippi State University. She has over 10 years of experience developing STEM curriculum and teaching physics, engineering, and biology.

Understand the bone growth process. Discover more about the hormones regulating bone growth, the bone formation process at various stages, and bone growth disorders. Updated: 02/24/2022

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Bone Growth and Development

Bone is responsible for providing the body with its structure, protecting important organs like the heart, lungs, and brain, and calcium storage. This important biological material must grow and change as humans grow and change. How do bones grow in length? Bones grow in length at the epiphyseal plate throughout childhood and adolescence, usually ending in the early or mid-20s. Cartilage is formed in a matrix near the epiphyseal plate by cells called chondrocytes, which multiply through mitosis. Once these cells have died, new cells called osteoblasts move into the matrix and transform it into bone through a process called ossification. Ossification is the transformation of cartilage into bone, stemming out from an ossification center.

Many factors impact the speed and amount of bone growth. Age and genetic makeup usually dictate how much bone is created at any given time. The bone growth itself is managed by hormones, which will be covered in greater detail later in this lesson. This process is a long one, usually beginning at three months of age and continuing until the early or mid-20s.

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  • 0:00 Overview of Bone Growth
  • 0:33 Early Bone Formation…
  • 1:43 Bone Growth in Childhood
  • 2:34 Hormones Regulating…
  • 3:59 Nutrition, Exercise,…
  • 5:38 Lesson Summary
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What Hormones Affect Bone Growth?

Bone growth is impacted and regulated by hormones from several places in the body. What hormones affect bone growth? Here is an incomplete list of some hormones that influence bone growth:

  • Estrogen is produced by both males and females, but females produce considerably more. The role of estrogen in bone growth is still being studied, but it regulates bone resorption in both men and women. It is also important for maintaining bone formation.
  • Testosterone is produced by both males and females, but males produce considerably more. It is important in maintaining bone formation.
  • Growth Hormone (GH) is the most important hormone for bone growth in children. It is secreted by the anterior pituitary gland. It increases bone turnover by increasing the number of osteoblasts, and how hard those osteoblasts are working.
  • Calcitonin inhibits the breakdown of bone and helps protect the body from calcium levels becoming too high in the blood.
  • Parathyroid hormone (PTH) maintains the level of bone calcium and stimulates bone formation.

Early Bone Formation

Ossification is the transformation of cartilage into bone, stemming out from an ossification center. Short bones usually have just one ossification center, but long bones like the femur can have as many as three ossification centers. These are sometimes called growth plates. Bones like the femur have a growth plate near each end.

In early bone formation, the primary ossification center appears first and begins to ossify cartilage. Secondary ossification centers appear afterward if more than one ossification center is required in that bone. Most primary ossification centers appear in utero before a baby is born. Most secondary ossification centers appear after birth.

Once the body is done growing, the epiphyseal plate itself is ossified and only appears as a line in the bone. Damage to the growth plate can result in malformed bones that grow improperly or not at all. The lines left behind by growth plates are detailed in the following diagram.


Lines formed by ossified growth plates are highlighted in this diagram. Ossified growth plates indicate that this body is done lengthening bone at this site.

Femur diagram


Bone Growth in Childhood

Bones are usually developed by the early or mid-20s. Before that time, bone growth is continually happening, from even before the child is born. To fit through the pelvis, the skull of the baby isn't complete. Fontanels, which are soft spots on the baby's skull, allow the flexible plates of the neonatal skull to overlap and become small enough to fit through the pelvis. Over time, the soft spots close and ossify, creating a mature skull, pictured here:


A mature human skull is completely ossified, providing a protective bony casing for the brain, but fissures, where fontanels were previously present, are visible.

Mature skull


As many as 40% of girl children and more than 50% of boy children break a bone at some time in their childhood. This is partly due to roughhousing, vigorous play, and accidents. However, there is a biological component as well. Bone growth isn't complete in childhood.

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Frequently Asked Questions

What disease affects bone growth?

There are many diseases that impact bone growth. Osteoporosis, which is the most common metabolic bone growth disorder, commonly afflicts older adults.

How do bones grow in length?

Bones grow in length at the epiphyseal plate. Cartilage is formed in a matrix near the epiphyseal plate by cells called chondrocytes. Once these cells have died, new cells called osteoblasts move into the matrix and transform it into bone through a process called ossification. Ossification is the transformation of cartilage into bone.

What can cause extra bone growth?

Extra bone growth can be caused by hormonal imbalances, particularly an overage of Growth Hormone (GH) secreted by the pituitary gland. There are genetic disorders that can result in extra bone growth as well.

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