osteoclast

Examples of osteoclast in the following topics:

• Bone Tissue and the Effects of Aging

  • The osteoclasts are multi-nucleated cells that contain numerous mitochondria and lysosomes .
  • Osteoclasts are generally present on the outer layer of bone, just beneath the periosteum.
  • Attachment of the osteoclast to the osteon begins the process.
  • This decreases the number and activity of osteoclasts, resulting in less bone resorption.
  • Osteoclast, displaying many nuclei within its "foamy" cytoplasm, above a bone's surface

• Cell Types in Bones

  • The osteoblast, osteoclast, osteocyte, and osteoprogenitor bone cells are responsible for the growing, shaping, and maintenance of bones.
  • Bone consists of four types of cells: osteoblasts, osteoclasts, osteocytes, and osteoprogenitor (or osteogenic) cells .
  • Osteoclasts continually break down old bone while osteoblasts continually form new bone.
  • The ongoing balance between osteoblasts and osteoclasts is responsible for the constant, but subtle, reshaping of bone.
  • Osteoclasts develop from monocytes and macrophages and differ in appearance from other bone cells.

• Stages of Bone Development

  • This occurs with the synchronized action of osteoclasts and osteoblasts, cells that resorb and deposit bone, respectively.
  • Osteoblasts and osteoclasts, coupled together via paracrine cell signalling, are referred to as bone remodeling unit.
  • The bone remodeling period consists of the duration of the resorption, the osteoclastic reversal (the phase marked by shifting of resorption processes into formative processes), and the formation periods of bone growth and development.
  • Bone tissue is removed by osteoclasts, and then new bone tissue is formed by osteoblasts.

• Bone Remodeling

  • Osteoblasts and osteoclasts, coupled together via paracrine cell signaling, are referred to as bone remodeling units.
  • The action of osteoblasts and osteoclasts are controlled by a number of chemical factors that either promote or inhibit the activity of the bone remodeling cells, controlling the rate at which bone is made, destroyed, or changed in shape.
  • Fibroblast growth factor activates various cells of the bone marrow including osteoclasts and osteoblasts.
  • Clinical Note: Osteoporosis means porous bone, which is caused by an over-reaction to osteoclastic bone resorption, and makes bones quite fragile for the elderly.
  • Bone tissue is removed by osteoclasts, and then new bone tissue is formed by osteoblasts.

• Postnatal Bone Growth

  • Bone is a dynamic tissue that is constantly being reshaped by osteoblasts and osteoclasts.
  • Osteoblasts produce bone matrix and mineral, and osteoclasts break down the tissue.
  • Osteoblasts begin depositing concentric lamellae of matrix, while osteoclasts dissolve the temporarily calcified cartilage.
  • Osteoclasts in the interior cavity continue to degrade bone until its ultimate thickness is achieved.
  • Pictured is part of a longitudinal section of a rabbit's developing femur, with parts including: a) Flattened cartilage cells; b) Enlarged cartilage cells; c), d) Newly formed bone; e) Osteoblasts; f) Giant cells or osteoclasts; g), h) Shrunken cartilage cells.

• Bone Remodeling and Repair

  • It involves the processes of bone deposition or bone production done by osteoblasts and bone resorption done by osteoclasts, which break down old bone.
  • This is similar to the endochondral formation of bone when cartilage becomes ossified; osteoblasts, osteoclasts, and bone matrix are present.
  • Bone remodeling: The bony callus is then remodelled by osteoclasts and osteoblasts, with excess material on the exterior of the bone and within the medullary cavity being removed.

• Bone Development

  • Blood vessels invade the cavities, while osteoblasts and osteoclasts modify the calcified cartilage matrix into spongy bone.
  • Osteoclasts then break down some of the spongy bone to create a marrow, or medullary cavity, in the center of the diaphysis.

• Hormonal Control of Blood Calcium Levels

  • In the skeleton, PTH stimulates osteoclasts, which are cells that cause bone to be reabsorbed, releasing calcium from bone into the blood.
  • Calcitonin decreases blood calcium levels by inhibiting osteoclasts, stimulating osteoblasts, and stimulating calcium excretion by the kidneys.

• Connective Tissues: Bone, Adipose, and Blood

  • There are three types of cells in bone: osteoblasts, osteocytes, and osteoclasts.
  • Osteoclasts are active in breaking down bone for bone remodeling, providing access to calcium stored in tissues in order to release it into the blood.
  • Osteoclasts are usually found on the surface of the tissue.
  • Osteoclasts bore tunnels into the bone and osteocytes are found in the lacunae.

• Overview of the Parathyroid Glands

  • PTH has effects antagonistic to those of calcitonin by increasing blood calcium levels by stimulating osteoclasts to break down bone and release calcium.