Osteology Summary — Bones for Beginners
Dr. AJ Petto Bones tissue is characterized by a matrix that is 35% organic and 65% inorganic or mineral; the mineral component of the matrix is hydroxyapatite; the organic component is collagen. Hydroxyapatite gives strength and collagen gives flexibility to the tissue. Ossification: The production of bone (ossification) occurs by two processes and the bones of the skeleton are often classified as endochondral or intramembranous based on the mode of ossification. Intramembranous - this bone originates as osteoprogenitor cells that are embedded in c.t. membranes; these cells migrate to be near the blood supply in the membrane, differentiating into osteoblasts, and produce bone within the membrane. Some skull bones and the clavicle are intramembranous. Endochondral- begins with a “model” of the bone in hyaline cartilage; chondrocytes hypertrophy (greatly enlarge); the matrix begins to mineralize and the chondrocytes dies leaving the large lacunae empty; blood vessels and osteoblasts invade from periosteum and turn mineralized cartilage into bone. Gross Morphology: To the unaided eye, bone has two types of appearances. Compact bone looks dense and solid. Trabecular (also spongy or cancellous) bone has a “honeycombed” appearance with many spaces between “branches” of bone. When a bone contains both types, there is usually a layer of compact bone forming a sort of “shell” around the bone, with trabecular bone filling some or all of the inner portion. Compact bone gives strength, shape and protection to the bone; trabecular bone gives strategic support while saving weight. In many bones, the trabecular bone is the location of the red marrow where blood cells and some immune cells are formed.
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