1. 5. List and describe the function of the three major types of cells found in bones. (6)
Osteoblasts (bone-forming): cells that form new bone. They come from bone marrow and are related to
structural cells. Osteoblasts produce new bones called “osteoid” which is made of bone collagen and
other protein. Then they control calcium and mineral deposition and are found on the surface of the
new bone. When the team of osteoblasts has finished filling in a cavity, the cells become flat and look
like pancakes. They line the surface of the bone. These old osteoblasts are also called lining cells. They
regulate passage of calcium into and out of the bone, and they respond to hormones by making special
proteins that activate the osteoclasts.
Osteoclasts (bone-absorbing): cells that degrade bone to initiate normal bone remodeling and mediate
bone loss in pathologic conditions by increasing their resorptive activity. Osteoclasts regulate the
differentiation of osteoblast precursors and the movement of hematopoietic stem cells from the bone
marrow to the bloodstream. They also participate in immune responses and secrete cytokines that can
affect their own functions and those of other cells in inflammatory and neoplastic processes affecting
bone.
Osteocytes: descend from osteoblasts and are formed by the incorporation of osteoblasts into the bone
matrix. Osteocytes remain in contact with each other and with cells on the bone surface. Osteocytes are
actively involved in bone turnover, the osteocyte network is through its large cell-matrix contact surface
involved in ion exchange, and they are the mechanosensory cells of bone and play a pivotal role in
functional adaptation of bone.
6. List and discuss the five homeostatic functions of bones. (7)
Mechanical support of soft tissues
Levers for muscle action
Protection of the central nervous system
Release of calcium and other ions for the maintenance of a constant ionic environment in the
extracellular fluid
Housing and support of hemopoiesis