There are three types of cell in bone. Their functions are outlined below:

Osteoblasts

Osteoblasts line the inner (endosteal) and outer (periosteal) surfaces of the bone. Osteoblasts synthesize organic bone matrix (osteoid) and collagen. Osteoblasts also synthesize the enzyme alkaline phosphatase and initiate the process of mineralization. Osteoblasts represent the final stage of differentaition of pluripotential stem cell in the bone marrow. They typically live about three months before flattening to become metabolically inactive bone lining cells. About 10-15% of osteoblasts become osteocytes.

Osteocytes

The most abundant cell in bone is the osteocyte. The cells known as osteocytes are formed from metabolically inactive osteoblasts which have become entombed in a newly formed bone matrix during active bone formation. Osteocytes no longer secrete osteoid; however they do maintain their sensitivity to PTH and vitamin D and participate in calcium regulation. Osteocytes are interconnected by tiny channels called canaliculi.

Osteoclasts

Osteoclasts are multi-nucleated giant cells that resorb bone by enzymatic degradation. These cells are characterized by a ruffled border and lie in bone resorption pits called Howship's lacunae. Osteoclasts are related to hematopoietic cell lines (monocytes, macrophages). Osteoclasts are seen in increased numbers in diseases with increased bone turnover.

How many types of bone cells can you identify in this histological slide? What biological process does it illustrate? from the PEIR pathology library © Copyright UAB and the UAB Research Foundation, 1999-2000. All rights reserved. Check This is a high magnification view of bone remodeling during fracture healing; osteoclasts, osteocytes and osteoblasts are shown. adapted from from the PEIR pathology library © Copyright UAB and the UAB Research Foundation, 1999-2000. All rights reserved. Close