Bones: The Living Framework of the Human Body

1. Bones: The Living Framework of the Human Body Eva L. Murdoch, PhD Assistant Professor Department of Natural Sciences Joliet Junior College http://www.youtube.com/watch?v=FufL80hJsP8

2. The Skeleton • Provides structural support for the entire body • Stores minerals • Protects soft tissues • Houses red and yellow bone marrow • Serves as levers, on which skeletal muscles pull to generate motion

3. Bone Formation and Growth • Bone formation • 6 weeks (embryo 0.5”) • Bone growth • Continues during development in utero • Continues through childhood • Stops at about age 25 • Hormonal regulation • Growth hormone & Thyroxin – stimulate bone cells to produce bone matrix  growth • Sex hormones (estrogen & testosterone) speed up bone synthesis at puberty  growth stops within few years

4. The Human Body • The human body: collection of cells and cell products • Cells: smallest living unit performing vital functions • Cell products: non-living, often proteins, also perform vital functions

5. Bone Tissue • Living tissue composed of: • Several cell types – osteocytes, osteoblasts, osteoclasts • Matrix - cell products (collagen fibers) and inorganic salts (calcium phosphate)

7. Bone Tissue Matrix: Protein-Crystal Combination: Bone Cells: Osteocytes: maintain protein and mineral content of bone matrix Osteoblasts: produce bone matrix Osteoclasts: remove and recycle bone matrix • Collagen fibers: exceptionally strong protein, when subjected to tension – stronger than steel • Calcium phosphate crystals: very hard, withstanding compression, but brittle when exposed to twisting Ca3(PO4)2

8. Bone Tissue Ca2+ • Bone: • Strong, somewhat flexible and highly resistant to shattering. • On par with the best steel-reinforced concrete • Even better, bone undergoes changes (remodeling), and can repair itself after injury Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+

9. Bone Remodeling • Maintaining bone mass is a balance between bone cells creating bone matrix and bone cells dissolving bone matrix. • Recycle & renewal of bone matrix • Maintenance of mineral reserve, supply of minerals in body fluids (blood) • Involves osteocytes, osteoblasts, and osteoclasts • Turnover rate: varies • Deposition > removal, bone stronger • Deposition < removal, bone  weaker • Heavy-metal ion deposition into bone matrix • Lead (Pb), cobalt (Co), uranium (U), plutonium (Pu)

10. Bone: Calcium Homeostasis Calcium – essential ion for all cells Bones: calcium reserve Calcium homeostasis: maintenance of sufficient calcium ion level in blood Calcium: high in blood Calcitonin: decrease of calcium in blood, resulting in increased bone production Calcium: low in blood Parathyroid Hormone: increase of calcium in blood, due to an increase in bone breakdown

11. The Effects of Exercise on Bone • Bone adapts to physical stress: • Mineral crystals in bone matrix create small electrical currents • Osteoblasts: produce bone matrix • Electrical currents: repair of severe fractures • Bone surfaces change • Thicker, larger bumps & ridges: muscle attachment

12. Bone and Aging • Bone: thinner & weaker • Osteopenia– b/n ages 30 & 40 women lose 8% of bone mass/decade, men 3% • Mainly at ends of long bones, vertebrae& jaws • Causing fragile limbs, reduction in height, and tooth loss • Osteoporosis– age > 45, severe bone loss, affects: 29% women & 18% man • Fractures due to normal physical activity (standing) • Accelerated in women: loss of estrogen • Cancer (bone marrow, breast and other) – risk factor for osteoporosis • osteoclast activating factors

13. Normal spongy bone • Things I can do to slow down the effects of aging and assure optimum bone mass. • Adequate diet • Weight bearing exercise (daily) • Monitor hormone levels associated with bone mass Spongy bone in osteoporosis