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Bone Growth and Development a Complete Guide

Two human femur bones
Contents

Photo by MAKY.OREL, CC0, via Wikimedia Commons

Bones are an important part of our body that support all the tissues of the body. Bone growth and development are regulated by hormones, mainly growth hormone from the pituitary gland and the sex hormones made by the ovaries and testes.

Parathyroid hormone (from the parathyroid glands), calcitonin (from the thyroid) and vitamin D also help control how calcium moves into and out of bone.

PHYSIOLOGY OF BONES

  • Bones allow our body to move from one place to another along with the movement of the attached muscles.
  • Bones make our body shape, produce many types of blood cells, and protect our internal organs.
  • Bones also determine your body height.
  • Disorders of bone growth can cause short stature. Bone growth begins before you are born and continues throughout childhood and adolescence. The adult body has 206 bones, some of them long bones and some short.

BONES & JOINTS

Bones meet each other at JOINTS, also called articulations. Bones are held together at joints by ligaments, cartilage or fibrous tissue.

In the movable (synovial) joints, a membrane makes synovial fluid that lubricates the joint, and cartilage covers the bone ends so they glide smoothly. Joints differ in structure and function.

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The structural classification divides the joints into three types depending on the composition of the joint and the presence or absence of a cavity in the joint. These may be

  • fibrous
  • cartilaginous
  • synovial joints.

The functional classification divides the joints into three categories according to their functions:

  • synarthroses
  • amphiarthroses
  • diarthrosis

Bone growth and development is a critical process influenced by vitamins, minerals and hormones, including vitamin D, parathyroid hormone, calcitonin, growth hormone, estrogen and testosterone. These hormones need to be in balance to keep bone growth normal.

Bone Growth Factors

Our body produces many growth factors that are responsible for bone growth and development. Hormonal factors are insulin-like growth factor 1, insulin-like growth factor 2, fibroblast growth factors, transforming growth factors, parathyroid hormones, etc. Vitamins for bone growth are vitamin D and minerals for bone density are phosphorus, magnesium, calcium, etc. These factors work very harmoniously to control the proper procedure of bone formation i.e bone proliferation, bone maturation, and mineralization.

TYPES OF BONE

Bones are divided into two types that are different in structure and functions. Many bones have both types of bone tissues.

1- COMPACT BONE

This also called cortical bone. It is a thick and dense part of the bone. This is the site where ligaments and tendons are attached. Therefore, it works as a mechanical part.

2- Trabecular bone

It also is known as spongy bone or cancellous bone. This bone has trabeculae (meshwork) in the bone marrow and located within the layers of compact bone. This type of bone is involved in metabolic functions.

What Are The Types Of Bones Cells And What They Do?

There are four main types of bone cells. The SEER training module on bone development describes the three that build and remodel bone: osteoblasts, osteocytes and osteoclasts.

Osteoblasts

Involved in bone formation. Therefore, also known as bone forming cells.

Osteocytes

Mature bone cells. They come from osteoblasts that have become trapped in the bone matrix they made.

Osteoclasts

Cells that break down and reabsorb bone. The balance between osteoblasts and osteoclasts keeps bone tissue healthy.

Lining cells

These cells come from osteoblasts that are flattened. They cover resting bone surfaces.

How Bone Formation Process Occurs?

Bone formation occurs during your fetal life, childhood life until adolescence. Ossification is the process of bone formation and bone growth from fetal life to childhood. This ossification comprises of two parts i.e

Intramembranous ossification

This is the direct laying down of bone into the primitive mesenchymal connective tissue.

Endochondral ossification.

In this process, a cartilage model is gradually replaced by bone. Most bones of the skeleton form this way. Two ossifications occur during complete bone growth and development. They are

  • Primary Ossification
  • Secondary Ossification

Three Stages of Bone Growth

There are three stages of bone growth and development, during which the whole bone is formed. These stages are

  • Bone formation during fetal life
  • Bone formation during childhood
  • Bone formation during adolescence

1- Bone Formation during Fetal Life

Parts of the skeleton start to form in the first few weeks after conception. By the end of the eighth week, the skeletal pattern is laid down in cartilage and membranes, and ossification begins.

In long bones, cartilage forms a model of the future bone. Osteoblasts then invade this cartilage and begin to produce osteoid.

Osteoid is the unmineralized bone matrix, made mostly of collagen. It then hardens as calcium phosphate minerals are deposited in it. This process starts in the center of the bone, at the primary ossification center.

Bone formation then moves outward from the center toward the ends. As the process continues, new blood vessels grow into the bone. The ends of the bones are still covered by cartilage.

2- Bone Growth at Childhood

As you grow older, your bones need to grow longer, especially at the ends of the bones. Bones grow in length at the growth plates (epiphyseal plates), where new cartilage keeps forming and is then replaced by bone.

Bones keep growing longer until the growth plates close, usually between the late teens and early twenties.

3- Bone Growth at Adolescence

Bones keep growing during adolescence by the same endochondral process, until the epiphyseal plate (the growth plate near each end of the bone) turns to bone and the end of the bone fuses with the shaft (diaphysis). After that, bones can no longer grow in length.

THE FIRST BONE TO BE OSSIFIED

The clavicle is the first bone that is ossified in fetal life but the last to complete epiphyseal union. Every bone takes a different time to complete its ossification.

Ossification is the process of bone formation and bone growth from fetal life to childhood. This ossification comprises two parts i.e intramembranous ossification and Endochondral ossification.

If you are worried about a child's growth, talk with a pediatrician. They can check growth over time and look for medical causes.

HP Thoughts: Ossification during youth but osteoporosis during advanced age. What causes the latter? Read our post to find out: Osteoporosis.

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