Remodeling and Osteoporosis

Bone Remodeling

Once your bones hit maximum length, osteoblasts don’t just stop their job, like going on strike.  They continue to lay down bone throughout your lifetime.  Your skeleton, today, is not the skeleton you were born with.  Throughout your lifetime, osteoclasts break down bone using osteolysis in a process officially called resorption.  At the same time, osteoblasts are continuing to replace or recycle that bone in a process called depositionThe process of bone matrix formation by osteoblasts..  Is this ossification?  Not really.  We are not replacing a cartilageA flexible connective tissue found in joints, the ear, nose, and rib cage. Cartilage can be of three model here, so, no, it’s not officially ossification.  This is just deposition.

You can see the statistics here about the rate at which your bone tissue turns over.  You could say that if you are 50 years old, you’ve had about 5 skeletons in your lifetime.  Deposition is only part of the process of what is referred to as bone remodeling.  OsteoclastsBone-resorbing cells that break down bone matrix. breakdown the bone, so that it can be turned over or replaced with new bone.  Their use of lysosomes to lyse bone tissue is called osteolysis. The overall process of breaking down bone in your adult life is called resorption.  I once had a student ask why it was REsorption and not Absorption…which is kinda a good question.  I had to think about it for a minute.  Absorption occurs in your small intestine.  This word officially refers to the process of taking in things from the external environment. The collagenA structural protein in the dermis that provides strength and elasticity. and calcium released from bone by osteoclasts enter the blood again. This makes it resorption.  Yes, I, too, feel like it should reabsorptionThe process of fluid moving back into capillaries from surrounding tissues due to colloid osmotic p. 

If you gain or lose weight, the osteoblasts and osteoclasts will adjust to the demands of the muscle actions.  If you break a bone, as I mention in another mini-lecture, you remodel that bone repeatedly. This process continues until it gets back to normal.  This can take months, years sometimes.  

Osteoporosis

Many of us are familiar with the word osteoporosis. We have a vague definition of it as a bone disease for older women.  Osteoporosis results from too little osteoblast Bone-forming cells that secrete osteoid. activity.  The balance of remodeling gets out of whack.  Remodeling is a calculated replacement of the bone.  Osteoporosis is just the breakdown, not the deposition.  Estrogen is a big influence on the ability to deposit calcium in remodeling.  Without that estrogen, osteoblasts kinda lay back and do like 50% of their job.  The osteoclasts are working as usually, but the osteoblasts are not matching that pace.  If you have osteoporosis, just take calcium, right? No, without the estrogen to encourage the work ethic of the osteoblasts, that excess calcium consumed doesn’t matter.  The osteoblasts refuse to use it. 

What can you do?  Get your calcium in before menopauseThe natural cessation of menstruation and ovarian function..  Your body refuses to take up calcium without vitamin D.  Vitamin D is like an usher for calcium.  Vitamin D opens the door for calcium to enter.  You can take all the Vitamin D you want. Without sunlight exposure onto your skinThe body’s largest organ, providing protection and regulation., the vitamin D won’t get activated. It needs to be absorbed from your small intestine to activate.  Let’s recap, calcium, vitamin D, and sunlight.  All three or don’t bother. Before COVID, there was a group of old ladies in my town. They had an exercise group called Bone Builders. I don’t know if they still do it.  The idea is that you have lost estrogen, which encourages your osteoblasts to work. Without it, you could encourage them through influencing remodeling.  Perform exercises that increase muscle strength at key areas of weakness, such as the hips. The applied forces will encourage bone deposition. This is similar to what happens when you gain weight.