Bone Cells - Joliet Junior College

Bones: The Living Framework of
the Human Body
Eva L. Murdoch, PhD
Assistant Professor
Department of Natural Sciences
Joliet Junior College
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
- 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,
- Matrix - cell products (collagen fibers) and
inorganic salts (calcium phosphate)
Bone Tissue
• Matrix: Protein-Crystal
Collagen fibers: exceptionally
strong protein, when subjected to
tension – stronger than steel
Calcium phosphate crystals: very
hard, withstanding compression,
but brittle when exposed to
• Bone Cells:
Osteocytes: maintain protein and
mineral content of bone matrix
Osteoblasts: produce bone matrix
Osteoclasts: remove and recycle
bone matrix
Bone Tissue
• Bone:
– Strong, somewhat flexible and
highly resistant to shattering.
– On par with the best steelreinforced concrete
– Even better, bone undergoes
changes (remodeling), and can
repair itself after injury
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
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
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
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 &
• 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
• Accelerated in women: loss of estrogen
– Cancer (bone marrow, breast and other) –
risk factor for osteoporosis
• osteoclast activating factors
Normal spongy bone
 Things I can do to slow
down the effects of aging
and assure optimum
bone mass.
Spongy bone in osteoporosis
Adequate diet
Weight bearing exercise (daily)
Monitor hormone levels
associated with bone mass

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