Bones: The Living Framework of the Human Body

Eva L. Murdoch, PhDAssistant Professor

Department of Natural SciencesJoliet Junior College

http://www.youtube.com/watch?v=FufL80hJsP8

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

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

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

Bone Tissue

• Living tissue composed of: - Several cell types – osteocytes, osteoblasts,

osteoclasts

- Matrix - cell products (collagen fibers) and inorganic salts (calcium phosphate)

• Matrix: Protein-Crystal Combination:

- 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

• Bone Cells:

- Osteocytes: maintain protein and mineral content of bone matrix

- Osteoblasts: produce bone matrix- Osteoclasts: remove and recycle

bone matrix

Bone Tissue

Ca3(PO4)2

Ca2+

Ca2+

Ca2+

Ca2+

Ca2+

Ca2+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

Bone Tissue

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)

Bone: Calcium Homeostasis• Calcium – essential ion for all cells

− Bones: calcium reserve− Calcium homeostasis: maintenance of

sufficient calcium ion level in blood

1. Calcium: high in blood− Calcitonin: decrease of calcium in blood,

resulting in increased bone production

2. Calcium: low in blood− Parathyroid Hormone: increase of calcium in

blood, due to an increase in bone breakdown

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

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

Normal spongy bone

Spongy bone in osteoporosis

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