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

• 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.

• 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.

• Action of Thyroid Hormones

• Bone and Calcium Homeostasis

  • The process of bone resorption by the osteoclasts releases stored calcium into systemic circulation and is an important process for regulating calcium balance.

• Parathyroid Hormone

  • Parathyroid hormone acts on a bone to increase its blood calcium levels by stimulating osteoclasts to break down bone and release calcium into the bloodstream.

• Female Athlete Triad: Disordered Eating, Amenorrhea, and Premature Osteoporosis

  • With estrogen deficiency, the osteoclasts live longer and are therefore able to resorb more bone.
  • As osteoclasts break down bone, patients see a loss of bone mineral density.

• Paget's Disease

  • Initially, in Paget's disease there is a marked increase in the rate of bone resorption at localized areas caused by large and numerous osteoclasts.