Types of bone @(Model.HeadingTag)>
Bones may be described by their shape.
Long bones act as levers and help us move. The long bones are the humerus, ulna and radius in each arm and the femur, tibia and fibula in each leg.
Short bones provide support and help with movement. The bones in the wrists and ankles are short bones.
Flat bones shield and protect important organs. They are the bones of the skull, the breast bone (also called the sternum) and the ribs.
Irregular bones don’t fit into the other categories. The bones of the spine (called vertebrae) and the pelvis are irregular bones.
Cellular makeup of a bone @(Model.HeadingTag)>
Bones are made up of bone matrix and different types of cells.
Bone matrix @(Model.HeadingTag)>
Bone matrix (osteoid) is the tissue that surrounds bone cells. It contains minerals such as calcium and strong fibres called collagen. Together the minerals and collagen help make bones strong and stiff.
Bone cells @(Model.HeadingTag)>
There are 3 main types of bone cells.
Osteocytes are mature bone cells. They help control the amount of protein and minerals in the bone matrix.
Osteoblasts are immature bone cells. They make bone matrix, which can harden into bone. Osteoblasts are found on the outer and inner surfaces of bone. When an osteoblast is surrounded by bone matrix, it matures into an osteocyte.
Osteoclasts are bone cells that break down and remodel bones as they grow or if there is stress on the skeleton. Osteoclasts also help control blood calcium levels because they release calcium into the blood as they break down bone.
When osteoclasts work faster than osteoblasts, bone becomes weak. When osteoblasts work faster than osteoclasts, bone gets bigger and stronger.
Bone growth @(Model.HeadingTag)>
The growth of bone is controlled by
Long bones in the arms and legs, as well as the pelvis, develop from cartilage. These bones have growth plates that allow them to grow longer. The growth plates are made up of multiplying cartilage cells. Osteoblasts gradually replace cartilage with bone. Because girls mature at an earlier age than boys, their growth plates change into bone at an earlier age.
Some bones, including bones in the skull, the lower jaw (called the mandible) and the collarbone (called the clavicle), develop differently than the pelvis and the long bones in the arms and legs. These bones develop from a type of cell found in developing embryos, called a mesenchymal cell. Mesenchymal cells can change into the cells that make bone (called osteoblasts).
Abha Gupta, MD, MSc, FRCPC
Raveena Ramphal, MBChB, FRACP
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