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Osteoblasts, Osteoclasts, Calcium, and Bone Remodeling

Linda Crampton is an experienced teacher with a first-class honors degree in biology. She writes about the scientific basis of disease.

Our skeleton performs many vital jobs.

Our skeleton performs many vital jobs.

Impressive Structures With Multiple Functions

Bones are impressive structures that do vital jobs for us. They provide attachment sites for muscles and enable us to move. Some, such as the skull and ribs, protect organs. They also make our blood cells, store minerals such as calcium and release them when necessary, and store lipids, which are an energy reserve.

One very important function of bone is to send calcium into the bloodstream when the body needs it. Calcium is a vital chemical in our bodies. It's necessary for muscle contraction, blood clotting, nerve conduction, and other functions. It also provides strength to bones and teeth.

Specialized cells called osteoclasts break down bone to free the calcium. Cells known as osteoblasts deposit calcium into bone, remaking it. The process of replacing old bone with new bone is known as remodeling.

Types of Bone Tissue and Marrow

Two types of bone tissue exist. The outer layer of a bone is composed of compact or cortical tissue. This is a dense material with low porosity. Spongy tissue (also called cancellous or trabecular tissue) forms the inner part of bones. It's made of a network of solid bone enclosing many pores. Marrow is located in these pores.

Bone marrow is red or yellow in color. The red type makes blood cells and the yellow type stores lipids (fats). Bones in different areas of the body have different proportions of compact and spongy tissue as well as different types of marrow.

A complete osteon is located on the left and two incomplete ones are shown on the right.

A complete osteon is located on the left and two incomplete ones are shown on the right.

Compact or Cortical Bone

The unit or building block of compact bone is a cylindrical structure called an osteon. The name comes from the Greek word for bone.

  • An osteon contains a central canal called the Haversian canal. Blood vessels and nerves run through this structure.
  • A Haversian canal is surrounded by circular, concentric layers of tissue called lamellae. The lamellae are made of a material called bone matrix.
  • Bone matrix is made of a mineral called hydroxyapatite. This mineral contains calcium and phosphorus as well as a protein called collagen.
  • Extending from the Haversian canal and through the lamellae are small horizontal canals called canaliculi.
  • Lacunae are small cavities or chambers located between one lamella and the next. (The dark purple structures in the diagram above are the lacunae.) The osteocytes or mature bone cells are located in the lacunae.
  • Osteocytes are star-shaped cells. They have long extensions that project into the canaliculi.
  • The membrane that covers the outer surface of the bone is called the periosteum.

The word “Haversian” in the term “Haversian canal” is generally capitalized because it’s named after Clopton Havers. Havers was a physician who lived in England in the seventeenth century. He was the first person to describe the canal and may also have been its discoverer.

Spongy, Cancellous, or Trabecular Bone

Spongy bone looks like a honeycomb or latticework, as shown in the centre of the illustration below. Each rod of bone is called a trabecula or a spicule. Trabeculae don't contain osteons or Haversian canals. They do contain lamellae, or layers of bone matrix, but the lamellae are parallel to each other. The matrix contains lacunae and canaliculi, as well as osteocytes, osteoblasts, and osteoclasts. Nutrients move from the marrow in the pores of the lattice into the trabeculae. The nutrients nourish the cells in the bone.

Volkmann's canals are horizontal channels in bone that contain blood vessels connecting the vessels in the Haversian canals to each other and to the periosteum. They are also known as perforating canals.

Volkmann's canals are horizontal channels in bone that contain blood vessels connecting the vessels in the Haversian canals to each other and to the periosteum. They are also known as perforating canals.

When the amount of bone manufacture equals the amount of disintegration, the mass of a bone remains the same. At certain stages of our lives or under certain conditions, the amounts are different. In these cases, a bone's mass will change.

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Functions of Osteoblasts and Osteoclasts

Osteoblasts build new bone matrix and osteoclasts break it down. (I remember the difference in the words' meanings by the fact that the letter b in "osteoblast" is also the first letter of the word "build".)

The creation and destruction of bone, the communication between its cells, and the signaling processes that occur are complex activities. Scientists have discovered that osteoblasts make a protein hormone, which is known as osteocalcin. The functions of this hormone and the activities that take place in bone are still being investigated.

Facts About Osteoblasts

Osteoblasts are cuboidal cells that work as a group to form new bone. They contain a large quantity of rough endoplasmic reticulum, which makes and transports proteins. They also have a large Golgi complex, which acts as a packaging area for products manufactured by the cell.

The osteoblasts move over the matrix of a bone and deposit a protein mixture called osteoid. The osteoid contains a protein called collagen as its major component. Then the osteoblasts deposit minerals—including calcium—into the osteoid to make bone. The new material fills in the cavity formed by osteoclasts.

A group of osteoblasts making osteoid, which is shown at the center

A group of osteoblasts making osteoid, which is shown at the center


Some osteoblasts become trapped in the bone matrix and are transformed into osteocytes inside lacunae. Osteocytes are thought to be sensory cells that are involved in signaling processes inside the bone. They connect to other osteocytes through their projections, which extend through the canaliculi. They are the most abundant cells in bone and also appear to have the longest lifespan.

Some osteoblasts become flattened and turn into lining cells that cover the surface of the matrix instead of being transformed into osteocytes.

An osteoclast with multiple nuclei lying on top of bone. The cytosol (solution around the nuclei) has a typical "foamy" appearance.

An osteoclast with multiple nuclei lying on top of bone. The cytosol (solution around the nuclei) has a typical "foamy" appearance.

Facts About Osteoclasts

Unlike osteoblasts, osteoclasts contain more than one nucleus. They are large cells produced by the fusion of several smaller ones. Osteoclasts travel over the surface of the bone matrix and secrete acids and enzymes to disintegrate it, forming a little pit on the surface of the bone.

As an osteoclast becomes active, the surface that is contact with bone becomes ruffled. This increases the surface area for absorption of minerals. The minerals (in their ionic form) are absorbed into the osteoclast, which later releases them into the tissue fluid located between cells. From there, the ions enter the blood. The process of bone breakdown and mineral uptake by the osteoclasts is known as resorption.

Hormonal Control of Calcium Deposition and Release

Our thyroid gland is located in front of our trachea, or windpipe, and sometimes covers the base of the larynx, which leads to the trachea. The four parathyroid glands are located behind the larger thyroid gland, as shown in the illustration below.

The parathyroid glands make a hormone called parathyroid hormone (also known as PTH or parathormone), which stimulates the action of osteoclasts when the amount of calcium in the blood falls. The hormone causes the transfer of calcium from bone to blood. On the other hand, the thyroid gland makes a hormone called calcitonin that slows the activity of osteoclasts, decreasing bone breakdown. Parathyroid hormone seems to be the more significant of the two hormones.

Estrogen in females and testosterone in males help to maintain bone strength. Other hormones that have an influence on bone mass are growth hormone, which is made by the pituitary gland, and cortisol, which is made by the adrenal gland. Growth hormone increases bone mass while excess cortisol decreases it.

The thyroid and parathyroid glands play a role in bone remodeling.

The thyroid and parathyroid glands play a role in bone remodeling.

Bone Production and Resorption

In general, when someone performs regular weight-bearing exercise, the amount of bone production exceeds the amount of resorption and bones increase in size. On the other hand, if someone is bedridden, production falls and the net effect is bone loss.

Our stage of life also influences the behavior of our bones. Bone production predominates during growth while resorption tends to predominate as we age. Researchers have found that the amount of resorption becomes larger than the amount of production in our mid thirties, although the difference doesn't become significant until our forties or fifties. A nutritious diet, moderate exercise of the correct type, and a healthy lifestyle can slow resorption and stimulate the production of new bone as we age.

A green smoothie can a great drink to boost the calcium level in the body.

A green smoothie can a great drink to boost the calcium level in the body.

Worldwide, osteoporosis causes more than 8.9 million fractures annually, resulting in an osteoporotic fracture every 3 seconds

— International Osteoporosis Foundation

What Is Osteoporosis?

Osteoporosis is a disorder in which the bones become unusually porous and brittle and bone density decreases. The condition generally appears in older people, although it occurs in young ones as well. In osteoporosis, the amount of bone resorption is much higher than the amount of bone production.

Osteoporosis can occur in both males and females, but it's most common in post-menopausal women. After menopause, the amount of estrogen in a women's body decreases significantly. This increases the risk of weakened bones.

In the video below, a doctor describes osteoporosis. If you are concerned about the disorder, a visit to your own doctor would be a good idea. He or she will be able to diagnose the condition. The doctor will also be able to give you suggestions for dealing with the disorder, reducing the chance that osteoporosis will develop, and decreasing its damage if it does appear.

How to Help Keep Bones Strong

Some common tips for keeping bones strong are described below. They are also common suggestions for helping us to stay healthy in other respects. If you already have osteoporosis, however, don't do any exercises without consulting your doctor.

In order to strengthen bones and reduce the chance of osteoporosis development, good nutrition and sufficient (but not extreme) exercise are important. An adequate intake of both calcium and vitamin D is necessary. Vitamin D is needed for calcium absorption through the lining of the small intestine. Other nutrients are also needed for bone health, so a varied diet with lots of nutritious foods should be followed. Smoking should be avoided, since plenty of research shows that it weakens bones. Excessive alcohol intake does the same thing.

Someone who wants to use exercise as a tactic to prevent osteoporosis should do some research. Some types of exercise are great for maintaining general health but don't stimulate bone growth significantly. It's also important to do exercises that strengthen the high-risk bones for osteoporosis, which are the hips, spine, and wrists.

With care and effort, we can fight our body's tendency to reduce bone mass as we age. We can also reduce the chance of developing osteoporosis and slow its progression if it's already developed. Medications that can treat osteoporosis exist and may be helpful, but prevention is better than treatment.


This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

Questions & Answers

Question: What are your thoughts on Xgeva?

Answer: I'm not the right person to ask, since I'm not a doctor. There are many factors involved in choosing a prescribed medication. The likelihood of a benefit for the patient's particular condition, the potential side effects, the potential for harm, the patient's other ailments, and their general state of health all play a role in the choice. Your family doctor or a specialist who is familiar with your case would be the best person to consult.

Question: What nutritional foods stimulate the production of osteocalcin in osteoblasts?

Answer: Vitamin K is required for osteocalcin production. Leafy, dark green vegetables are a good source of the vitamin. It’s fat-soluble, so eating a small quantity of a healthy oil with the greens will help the vitamin to be absorbed.

© 2013 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on April 17, 2020:

Hi. I think you are referring to biophosphonates. I’m a science writer, not a doctor, however. Your physician will be able to advise you about the effects of biophosphonates in your specific medical situation.

pog57 on April 17, 2020:

I am told I need biosphomates for my osteoporosis. I do not want to take any drugs but my spine is at -3.1 and neck -3.0, my hip -2.4. My question is do biosphomates block osteoblasts?

Linda Crampton (author) from British Columbia, Canada on May 09, 2017:

Thank you for sharing your experience, Una. I hope your bone problems are solved. I would make sure that you check with your doctor about the time that should be spent in the sun without protection in order to make vitamin D and stay safe at the same time. There are several variables involved, including skin type and the UV index.

Una on May 09, 2017:

Thank you for this very informative article. My mother had severe osteoporosis and despite me being aware and spending years in the gym doing weight bearing exercises and eating healthy, I had a wrist fracture very recently (I am 61). A DEXA scan now revealed I have osteoporosis in my spine, osteopenia in my hip and severe osteoporosis in my arms.

I am now taking ADCAL-D3 daily and alendronic acid once a week The latter sounds horrible but I will take for 2 years and see what happens.

My problem, it turns out is, severe lack of vitamin D. I was always told to stay out of the sun because I have fair skin. From now on, I am getting out in the sun as much as I can. They say 20 mins a day sunbathing throughout the summer, gets us our Vitamin D. So it's not as if we have to be out all day every day. This article has helped a lot to fully understand how our bones work. thank you.

una on May 09, 2017:

thank you

Linda Crampton (author) from British Columbia, Canada on March 20, 2017:

I'm sorry that you have osteoporosis, Nadine. I hope you are able to manage it successfully. Your lifestyle certainly sounds healthy!

Nadine May from Cape Town, Western Cape, South Africa on March 20, 2017:

Wow this was very informative, especially me having Osteoporosis. I do my Yoga each morning and live a healthy lifestyle. Do not smoke or hardly drink any alcohol, but I must amid that I do not take and vitamins or other supplement for that matter.You have reminded me to get some.

Linda Crampton (author) from British Columbia, Canada on February 02, 2016:

Thank you so much, Taranwanderer. I appreciate all your comments a great deal.

Linda Crampton (author) from British Columbia, Canada on January 08, 2013:

Thanks for the visit and the comment, Dianna! It is a good idea to build bone strength while young and to be beware of osteoporosis, as you say. It's better to prevent osteoporosis - if we can - than to treat it.

Dianna Mendez on January 08, 2013:

I know elderly people who suffer from bone loss and wish they had known how to prevent it using advice posted here. It is a good thing to take vitamin D to prevent this and to enhance your body while young. Very well done!

Linda Crampton (author) from British Columbia, Canada on January 08, 2013:

Thank you very much for the comment, Kathi! I appreciate it. I'm sorry about your husband's problems, but I'm glad that yours have been detected in the beginning stages.

Kathi Mirto from Fennville on January 08, 2013:

Excellent hub! Pulled out all the stops! Thank you for teaching us this important information. My husband actually suffered all his life from bone loss, but I have beginning stages and so take my calcium and vitamin D religiously!

Linda Crampton (author) from British Columbia, Canada on January 07, 2013:

Thank you for the visit, Prasetio. I appreciate your kind comment and vote very much!

prasetio30 from malang-indonesia on January 07, 2013:

Very informative hub. Very well written and I learn many things about Osteoblasts and Osteoclasts. I had never heard about this before reading this hub. Good job, Alicia. You deserve to get my vote. Take care!


Linda Crampton (author) from British Columbia, Canada on January 07, 2013:

I'm sorry about your son's problems, leahlefler, especially when he's so young. I hope the situation is resolved sooIn and has a good outcome. Thank you for the comment and for sharing your son's experience.

Leah Lefler from Western New York on January 07, 2013:

This is a great article, Alicia. My son (age 5) was on high-dose proton pump inhibitors (PPIs) and we had to monitor his bone density because these drugs can cause osteoporosis and increase the risk of fractures. He's had an anti-reflux surgery now, but may end up on the drugs again if his next pH probe study shows continued reflux. Bone health is important!

Linda Crampton (author) from British Columbia, Canada on January 07, 2013:

Thank you very much for the comment and the interesting information, mperrottet. What an unpleasant experience for your friend! It's very sad when someone takes a medication with the expectation that it will help their condition and then finds that the medication actually makes the condition worse. Thanks for the votes.

Margaret Perrottet from San Antonio, FL on January 07, 2013:

I've been wondering about how biophosphates such as Fosimax effect the bone. They're finding out that more and more people are getting spontaneous femur fractures from taking these drugs, and they seem to be making bones brittle if taken for too long. I have a friend who is recovering from such a fracture, so I've been very interested in learning more about the remodeling process. Great hub - very informative. Voted up, interesting and useful.

Linda Crampton (author) from British Columbia, Canada on January 06, 2013:

Hi, Peggy. Thank you for the comment, which contains great information. I appreciate the votes and the share, too.

Peggy Woods from Houston, Texas on January 06, 2013:

While I studied all of this in nursing has been a while. The main reason that people should know and pay attention to this is to ward off things like osteoporosis which makes bones weak and much more susceptible to breaking. Weight bearing exercises even for people in nursing homes has proved it is never too late to adopt a healthy lifestyle with regard to our bones which after all have the job of supporting our bodies. Up votes and sharing.

Linda Crampton (author) from British Columbia, Canada on January 06, 2013:

Thank you very much for the comment, the vote and the share, Bill. I appreciate them all!

Bill De Giulio from Massachusetts on January 06, 2013:

Alicia. This is great information. We should all be aware of this as we age. Preventing Osteoporosis is key as we get older. Well done. Voting up, sharing, etc...

Linda Crampton (author) from British Columbia, Canada on January 05, 2013:

Thank you so much for the lovely comment and the votes, Tom. I hope that you had a great Christmas, too, and that this year is a wonderful one for you!

Thomas Silvia from Massachusetts on January 05, 2013:

Hi Alicia great hub and very informative and interesting and loaded with great information .

Vote up and more !!!

Hope you had a wonderful Christmas ! Wishing you all the best this New Year !

Linda Crampton (author) from British Columbia, Canada on January 05, 2013:

Thank you very much for the comment and for sharing the hub with your friends, drbj. I appreciate your visit.

drbj and sherry from south Florida on January 05, 2013:

Another excellent medical treatise, Alicia. This one on bones and calcium should be saved by all your readers and shared with those we know. So I shall.

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