Bone resorption is a natural process in the body where specialized cells break down bone tissue. This breakdown releases minerals from the bone into the bloodstream. It is a continuous and regulated process that is important for maintaining both bone health and the balance of calcium levels in the body.
The Mechanics of Bone Resorption
Bone resorption is carried out by specific cells called osteoclasts. These are large, multinucleated cells that attach to the bone surface. Once attached, the osteoclast creates a sealed compartment between its membrane and the bone surface.
Within this sealed area, the osteoclast releases hydrogen ions, creating an acidic environment. This acidity dissolves the inorganic mineral components of bone, primarily calcium and phosphate. Simultaneously, the osteoclast secretes enzymes into this acidic space. These enzymes break down the organic components of the bone matrix, including collagen. As bone is dissolved, its constituents are released into the bloodstream.
The Essential Role of Bone Resorption
Bone resorption plays a role in two functions: bone remodeling and calcium homeostasis. Bone remodeling is a continuous process where old or damaged bone tissue is removed and replaced with new bone. This constant renewal maintains the strength, integrity, and structure of the skeleton. Through this process, the body repairs micro-damage and adapts bone architecture to changing mechanical demands.
Bone resorption also helps maintain calcium homeostasis, the body’s ability to regulate calcium levels in the blood. Bones serve as a large reservoir for calcium, storing about 99% of the body’s total calcium. When blood calcium levels decrease, bone resorption is stimulated, causing osteoclasts to break down bone and release stored calcium into the bloodstream. This calcium is then available for various bodily functions, including nerve impulse transmission, muscle contraction, and blood clotting. Hormones like parathyroid hormone (PTH) regulate this release, ensuring blood calcium levels remain within a healthy range.
When Resorption Becomes Problematic
While bone resorption is a necessary process, problems arise when it becomes excessive or unbalanced compared to bone formation. When bone breakdown outpaces new bone formation, it leads to a net loss of bone mass. This imbalance can result in weakened and fragile bones, increasing fracture risk.
Osteoporosis is a common condition resulting from this imbalance, characterized by decreased bone density and deterioration of bone structure. Factors contributing to excessive bone resorption include aging, hormonal changes like reduced estrogen levels after menopause, and certain medical conditions or medications. Estrogen normally inhibits osteoclast activity, so its decline can lead to increased bone breakdown. Other conditions where abnormal bone resorption can occur include hyperparathyroidism, certain cancers like multiple myeloma, and periodontitis, which can lead to bone loss in the jaw.