Osteoporosis is accelerated bone loss. Normally, there is loss of bone mass with aging, perhaps 0.7% per year in adults. However, bone loss is greater in women past menopause than in men of the same age. The process of bone remodeling from resorption to matrix synthesis to mineralization normally takes about 8 months--a slow but constant process. Bone in older persons just isnt as efficient as bone in younger persons at maintaining itself--there is decreased activity of osteoblasts and decreased production of growth factors and bone matrix. (Sambrook and Cooper, 2006)This diagram illustrates changes in bone density with aging in women. The normal curve (A) steepens followingmenopause, but even by old age the risk for fracture is still low. A woman who begins with diminished bonedensity (B) even before menopause is at great risk, particularly with a more accelerated rate of bone loss.Interventions such as postmenopausal estrogen (with progesterone) therapy, the use of drugs such as the non-hormonal compound alendronate that diminishes osteoclast activity, and the use of diet and exercise regimenscan help to slow bone loss (C) but will not stop bone loss completely or restore prior bone density. Diet andexercise have a great benefit in younger women to help build up bone density and provide a greater reserveagainst bone loss with aging. (Winslow et al, 2009)
Bone is made of mineral + organic (mainly collagen) components Treated with hydrochloric acid to dissolve mineral leaves collagen component intactTreated with bleach (hypochlorite) to digest collagen leaves mineral component intact Collagen shrinkage on drying
Scanning electron microscopy image of the bone-cotton after immersion in simulated bodyfluid showing the formation of hydroxyapatite on the surface of the fibers.
A bat skeleton at day 80 ofembryonic development. Boneappears in red and cartilage inblue.
Skeleton of a 16 week old human fetus.Hardened bone appears yellow here. Gapsbetween the ends of bones, such as the ribsand spinal column, are filled with cartilage (notseen) that forms a matrix upon which hardbone forms. The pelvis (lower centre) and rightleg (lower right) are seen. At this stage ofdevelopment the foetus weighs 200 grams andhas a crown-rump length of up to 14centimetres. Stained with Alizarin red dye.
Lateral view Medial viewThese are 2 views of the same 12 week 92 mm CRL human fetus head, double stained to showboth cartilage (blue) and newly-formed bone (red). The head undergoes two different forms ofossification (endochondral and intramembranous) in separate regions of the skull.
Point-to-Ponder1. The tensile strength of bone (resists pulling forces) is due to: a. Osteoblasts b. Mineral salts c. Collagenous fibers2. The compressional strength (resist crushing) of bone is due to: a. Osteoblasts b. Mineral salts c. Collagenous fibers3. In aging, less collagen is deposited in bone tissue, so that more of the bone is composed of mineral salts. Predict the effect of these changes on a bone’s ability to resist the forces that cause a bone to break.3. The bone to the right… a. Has been demineralized. b. Has had its organic components removed.
Point-to-PonderPredict the flow of a nutrient from circulation to an osteocyte. List 5 structures.
Point-to-PonderA 15-year old football player is tackled during a game and the distal epiphyseal plate of the left femur is damaged.a. His left lower limb will not grow.b. His left thigh will not grow.c. His left thigh will be shorter than his right thigh.d. Recovery will be difficult.