Osseous Tissue (Bone Tissue)
1. Cells
•
•
•
Osteocytes— mature bone cells
Osteoblasts— bone-forming cells (germ cells or “bud” cells)
Osteoclasts —bone-destroying cells (“breakers”)
2. Matrix
A. primarily collagen fibers
flexibility
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)
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
Maintenance of Bone
bone
formation
osteoblasts
bone
reabsorption
osteoclasts
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
Hormonal effects
bone
formation
bone
reabsorption
osteoblasts
osteoclasts
Calcitonin
Parathyroid
hormone (PTH)
(CT)
from thyroid
from parathyroid
Increase bone mass
osteoblasts
osteoclasts
Before age 25
bone
formation
bone
reabsorption
osteoblasts
Age 25-50
osteoclasts
Decrease bone mass
osteoblasts
Age 50-on
osteoclasts
Bone Loss with Age
Stress effects
osteoblasts
osteoclasts
Stress increases bone density
http://www.youtube.com/watch?v=yFJ4iswRiu4&feature=related