Osseous Tissue (Bone Tissue)

1. Cells• Osteocytes— mature bone cells• Osteoblasts— bone-forming cells (germ cells or “bud” cells)• Osteoclasts —bone-destroying cells (“breakers”)

A. primarily collagen fibersflexibility tensile strength (the strength to endure stretching

forces) B. calcium salts (hardness)

contain calcium and phosphorus great compressional strength (the strength to endure

squeezing forces)

2. Matrix

Bone Remodeling• constant balance of bone

deposit and removal that occurs throughout your life

• bone deposit occurs at a greater rate when bone is injured

• bone reabsorption allows calcium of degraded bone matrix to move into the blood. About 10% of bone is

replaced every year in an adult skeleton

boneformation

bonereabsorption

osteoblasts osteoclasts

Maintenance of Bone

Calcium Negative Feedback Cycle

Control of Remodeling

Hormonal                                                       

–  Rising blood Ca2+ levels trigger the thyroid to release calcitonin 

–  Calcitonin stimulates calcium salt deposit in bone 

–  Falling blood Ca2+ levels signal the parathyroid glands to release Parathyroid hormone (PTH) 

–  PTH signals osteoclasts to degrade bone matrix and release Ca2+ into the blood 

boneformation

bonereabsorption

osteoblasts osteoclastsCalcitonin (CT)

from thyroidParathyroidhormone (PTH)

from parathyroid

Hormonal effects

bone

formation

bone

reabsorption

osteoblasts osteoclasts

Before age 25

Increase bone mass

boneformation

bonereabsorption

osteoblasts osteoclasts

Age 25-50

boneformation

bonereabsorption

osteoblasts osteoclasts

Age 50-on

Decrease bone mass

Bone Loss with Age

bone

formation

bone

reabsorption

osteoblasts osteoclasts

Stress effects

Stress increases bone density

http://www.youtube.com/watch?v=yFJ4iswRiu4&feature=related