How osteoclast destroy bone?

Osteoclasts destroy bone through a process of resorption, which involves several steps:

1. Cell adhesion and sealing zone formation:

- Osteoclasts adhere to the bone surface and form a specialized attachment structure called the sealing zone.

- The sealing zone prevents the leakage of enzymes and acid into the surrounding tissue.

2. Acid secretion:

- Osteoclasts secrete hydrochloric acid (HCl) and protons (H+) into the sealed space between the cell and the bone surface.

- This acidic environment lowers the pH and dissolves the mineral component of the bone, primarily hydroxyapatite.

3. Proteolytic enzyme secretion:

- Osteoclasts release proteolytic enzymes such as cathepsin K, matrix metallopeptidases (MMPs), and collagenases.

- These enzymes break down the organic components of the bone, including collagen, proteoglycans, and non-collagenous proteins.

4. Phagocytosis and degradation:

- The dissolved minerals and degraded organic matrix are taken up by the osteoclasts through phagocytosis.

- Phagosomes containing the bone debris fuse with lysosomes, forming phagolysosomes, where further degradation occurs.

5. Bone resorption:

- As a result of acid secretion, enzyme activity, and phagocytosis, the mineralized bone matrix is gradually resorbed, creating cavities or resorption pits on the bone surface.

- The bone fragments removed by the osteoclasts are released into the extracellular space.

It's important to note that osteoclasts' activity is essential for bone remodeling and is tightly regulated to maintain bone balance. Hormonal factors (such as parathyroid hormone and calcitonin), cytokines, and growth factors control osteoclastic activity. Dysregulation of osteoclastic resorption can lead to bone diseases such as osteoporosis, where excessive bone resorption occurs, or osteopetrosis, where bone formation exceeds bone resorption.