My Orthopaedic Surgeon

The primary responsibility of the skeleton is to withstand loadbearing. Bone is strong, it is stiff, it is tough. Bone can withstand extremely high loads, and will remain strong even following several million cycles of load.

There are two categories of bone cells. Osteoclasts are in the first category. They resorb (dissolve) the bone. The other category is the osteoblast family, which consists of osteoblasts that form bone, osteocytes that help maintain bone, and lining cells that cover the surface of the bone.
Educational resource materials by the American Society for Bone and Mineral Research ASBMR

During childhood, the long bones (in the arms, legs, and back) grow at the ends of the bones, whereas the flat bones (such as the skull) have a different pattern of growth. Adult bone actually continues to expand, although very slowly. Bone also continually undergoes remodeling, replacing old bone with new bone. Ordinary activity causes microscopic cracks in the bone, and these are dissolved and replaced with new bone. Remodeling also allows bone to respond to changes in mechanical forces. Thus, living bone is totally different from the skeleton in the closet.

Bone, the material that makes vertebrates distinct from other animals, has evolved over several hundred million years to become a remarkable tissue. Bone is a material that has the same strength as cast iron, but achieves this while remaining as light as wood.

Mature bone is composed of proteins and minerals. Approximately 60% the weight of the bone is mineral, mainly calcium and phosphate. The rest is water and matrix, which is formed before the mineral is deposited, and can be considered the scaffolding for the bone. About 90% of the matrix proteins are collagen, which is the most abundant protein in the body. Collagen is very strong and forms bone, cartilage, skin, and tendons.

Hormones are either small proteins (peptide hormones) or organic chemicals. The "classic" hormones are made in glands and travel to target organs via the bloodstream. Many other local hormones are made by one kind of cell, secreted into the surrounding fluid, to affect another kind of cell - - - or even to affect other cells of the same type. This page concentrates on the classic hormones made in the endocrine glands (parathyroid, thyroid, ovaries, testes, adrenal glands, and pituitary gland).

Flash Movie display explaining the pathophysiology of hypercalcuria, osteopenia and the effect of thiazides

Topics in the OrthoBullets Basic Science Section are displayed in the left hand panel. The initial topic is Types of Bone

Overview of bone structure, physiology, and function. Project of the Education Committee of the American Society for Bone and Mineral Research (ASBMR).