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Bone Building Cells

Bone can be defined as the rigid endoskeleton  of calcium phosphate and forms the endoskeleton of the body . The skeletal system formed by the bones  is the unit that is associated with the muscular system  that enables movement. It also is involved in supportingm protecting variopus organs in the body, is the site of synthesis of blood cells by haemopoeiesis and also as a storage of minerals like calcium. Bones have diverse structure in accordance with a diversity in function. ther e are  about 206 bones in the body (excluding the ossicles)  and the bone consists of  osseous tissue along with endosteium, periosteium ,nerve, blood vessels, lymph etc.  Bone building cells are cells  the osteoblasts  ,osteoclasts, osteocytes etc.

General structure of bone :
Bone is a type of connective tissue consisting of  a hard outer layer of compact bone tissue (dense bone.) with a 5% to 10% porosity producing the smooth white appreaance  and accounting of about 80% of adult bone mass.Internal to it lies the trabecular bone or the cancellus or spongy bonm with trabecular networks and porus in nature.It is basically a network of rod and plate like filaments that allows space for angiogenesis or growth of blood vessels
.Trabecular bone makes up about 20% of adult bone mass but has a surface area nearly 10 times  with a porosity of  aout even 90%.The cancellous bone consists of haversian sites and osteons .Besides , the blood is sourrounded by bone in the compact bone but it is reverse in cancellous bone.
                           bone building cells


Bone Building Cells

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In the bone , there are 5 types of bone building  cells:


  • These bone building cells arise from the osteoprogenitor cells in periosteum in bone marrow.
  • monomucleate cells, expressess all  receptors of the fibroblassts  in addition to genes for sialoprotein and  osteocalcin.
  • Consists of  high amount of   RER large Golgi apparatus with spherical nucleus.
  • Mesenchymal in origin


  • Produces osteoid, and type I collagen
  • mineralizes osteoid matrix,
  • Produces many minerals like zinc, copper ,sodium etc
  • Decreases with age
  • bone is constsantly replenished by osteoblasts.
  • Synthesizes alkalone phosphatase
  • Doesnot undergo cell division



  • Majority of the bone building cells.
  • Star shaped, most abundant in compact bone.
  • Cells with nucleus and thin ring of cytoplasm
  • Osteoblasts in   matrix   convert into  osteocyte
  • Interconnecting canaliculi are present  between osteocytes, space occupied by it is called lacuna
  • Mesenchymal in origin


  • Maintains daily metabolic exchange of nutrients and waste with blood
  • Involved in routine turnover of the matrix of the bone. through mechanosensory  means
  • Doenot secrete matrix
  • Performs osteocytic osteolysis


  • 40 ?m ijn diameter and  15 to 20 ,oval, closely placed nuclei.
  • Located in resorption bays or Howships lacunae.
  • Cytolasm homogenous and foamy due to many vesicles and vacuoles (lysosome with acid phosphatase)
  • Extensive Golgi and less RER
  • Has special cell membrane at site of bone resorption called  ruffled border  and is characteristic of osteoclast.
  • It increases surface area.
  • Develops form fusion of macrophage-monocyte cell line.


  • Removes bone tissue by  mineralizing the matrix  by bone resorption
  • Controls amount of bone tissue with osteoblasts
  •  Various cathepsins like B,C,D,E,G,L   are produced along with cathepsin K
  • cells attach to the resorbtion site by podosomes
  • Releases hydrogen ions through by action of carbonic anhydrase
  • regulated by several hormones like parathyroid


These are immaure cells that act as progenitors for  osteoblasts and may undergo division.

Osteoblast c ells in minimal activity ,almost inert , lining the bone .
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