An osteoclast is a type of bone cell that breaks down bone tissue. This function is critical in the maintenance, repair, and remodeling of bones of the vertebral skeleton. The osteoclast disassembles and digests the composite of hydrated protein and mineral at a molecular level by secreting acid and a collagenase, a process known as bone resorption. This process also helps regulate the level of blood calcium.
Light micrograph of an osteoclast displaying typical distinguishing characteristics: a large cell with multiple nuclei and a "foamy" cytosol.
Tartrate resistant acid phosphatase positive osteoclast in cell culture
Illustrated cross-section of an activated osteoclast
Osteoblasts are cells with a single nucleus that synthesize bone. However, in the process of bone formation, osteoblasts function in groups of connected cells. Individual cells cannot make bone. A group of organized osteoblasts together with the bone made by a unit of cells is usually called the osteon.
Osteoblasts (purple) rimming a bony spicule (pink - on diagonal of image). In this routinely fixed and decalcified (bone mineral removed) tissue, the osteoblasts have retracted and are separated from each other and from their underlying matrix. In living bone, the cells are linked by tight junctions and gap junctions, and integrated with underlying osteocytes and matrix H&E stain.
Major features of the bone-forming complex, the osteon, composed of osteoblasts and osteocytes.
Osteoblast (Wright Giemsa stain, 100x)
Light micrograph of decalcified cancellous bone displaying osteoblasts actively synthesizing osteoid, containing two osteocytes.
