Osteoclasts are large cells that cause the breakdown of osseous tissue.
True
False
The correct answer and explanation is:
Correct Answer: True
Osteoclasts are large, multinucleated cells responsible for the breakdown of bone tissue, a process known as bone resorption. These cells originate from the monocyte-macrophage lineage, which means they are derived from the same progenitor cells that produce certain white blood cells. Osteoclasts play a critical role in bone remodeling, a continuous process where old or damaged bone is removed and replaced with new bone tissue.
The primary function of osteoclasts is to dissolve the mineral matrix of bone and degrade the collagen fibers within the bone’s extracellular matrix. They achieve this by attaching tightly to the bone surface and creating a sealed-off area called the resorption lacuna. Within this area, the osteoclast secretes hydrogen ions and lysosomal enzymes such as cathepsin K. The hydrogen ions lower the pH, which helps dissolve the mineral content, primarily calcium phosphate, while the enzymes break down the organic matrix, mainly type I collagen.
The activity of osteoclasts is essential for several physiological processes. These include maintaining calcium and phosphate levels in the blood, shaping bones during growth, and repairing micro-damage in the skeletal structure. An imbalance in osteoclast activity can lead to various bone disorders. For instance, overactive osteoclasts can result in conditions like osteoporosis, where bone mass is reduced, making bones more fragile. In contrast, underactive osteoclasts can lead to osteopetrosis, a condition characterized by overly dense bones due to reduced resorption.
Osteoclast activity is regulated by several hormones and signaling molecules, including parathyroid hormone (PTH), calcitonin, and receptor activator of nuclear factor kappa-Β ligand (RANKL). RANKL, in particular, plays a central role in osteoclast differentiation and activation. Understanding the function of osteoclasts is vital for developing treatments for metabolic bone diseases.