Osteoblast

Although bone looks like a hard, unchanging material, it is actually living tissue. Osteoblasts form a single layer along bone surfaces, such as the inner side of the periosteum—the membrane covering the outside of bone—or the surfaces lining spaces within bone. This is because bone formation takes place at the surface.

Osteoblasts do their work in three main stages.

1. Building the framework for bone — First, they secrete a soft bone matrix called osteoid, made primarily of collagen. This is similar to assembling a framework of reinforcing steel bars. 2. Filling it with minerals — Minerals made of calcium and phosphorus accumulate in this framework, making it hard. Osteoblasts release enzymes and other substances that help this process take place. 3. Becoming trapped and transforming — Some osteoblasts, once their work is done, become trapped in the bone they have made and turn into osteocytes. Osteocytes connect in a network within bone and act as sensors that detect the forces placed on it. The others remain flattened and resting on the bone surface or disappear.

Osteoblasts develop from stem cells within bone. These stem cells share a common origin with, and can also differentiate into, other connective tissue cells, such as cartilage cells and fibroblasts. In other words, bone, fascia, and cartilage are not distant relatives: they belong to the same connective tissue family.

Osteoblasts always work in partnership with osteoclasts, the cells that break down bone. When osteoclasts remove old areas with microscopic cracks, osteoblasts fill those sites with new bone. This cycle is called bone remodeling. A substantial portion of adult bone is understood to be replaced with new bone over a period ranging from a few years to a little over ten years. In childhood, formation greatly outpaces breakdown, allowing children to grow taller and their bones to become thicker. With age, the balance tends to shift toward breakdown. Osteoporosis is a typical condition in which bone mineral density decreases as a result.

Integrative Manual Therapy (IMT) views bone as connective tissue in its most hardened form. The book explains that, although bone was once regarded mainly as a support for muscles and ligaments, it is now considered one of the body's most metabolically active structures. Osteoblasts are introduced as the cells that build the framework of this living bone.

This approach considers connective tissue to form an uninterrupted continuum, from the fascia beneath the skin to the periosteum surrounding bone. It therefore views manual work on fascia as potentially extending to nearby bone tissue. The perspective is that cells need to receive appropriate stimulation for the body in order to do their work.

We cannot feel osteoblasts at work in our bodies. Their work does, however, show up in what we call bone health. The idea that people who ran around and played a lot as children have strong bones, or that prolonged bed rest weakens bones, is connected to osteoblast responses. This is because bone tends to grow stronger in the direction of the forces placed on it and to diminish when little force is applied. This is explained by Wolff's law.

A broken bone also joins back together over time because osteoblasts gather at the fracture site and make new bone. This usually takes place over several weeks to several months.

• Weight-bearing exercise — Movements that involve bearing weight through the ground, such as walking, climbing stairs, and light jogging, stimulate bone. Swimming and cycling are good for the heart but provide relatively less stimulation to bone.
• Strength training — The pull of muscles on bone also provides beneficial stimulation for bone.
• Calcium, protein, and vitamin D — These are the building materials for bone. Get calcium from milk, tofu, anchovies, and leafy vegetables, and get some sunlight for vitamin D.
• Cutting back on smoking and heavy drinking — Both are known to be habits that are harmful to bone health.

A bone mineral density test can check whether your bones have weakened. Have this checked regularly after menopause or in older age.