1. Skeletal and Muscular System

2. Functions of Skeletal System
1) Support - keep body upright, support organs, tissues
2) Protection - delicate organs surrounded or cradled by bony parts
3) Storage of minerals (calcium, phosphates) and lipids
98% of body’s calcium found in bones
yellow marrow contains fat, is in shafts of bones
4) Blood cell production - blood cells made here, in red marrow in the ends of bones
5) Leverage - produces movements with skeletal muscles

3. Skeleton 206 bones in human body 6 are middle ear bones
Axial Skeleton – Skull, vertebral column, rib cage
is found in center or axis of body
Appendicular Skeleton – bones of shoulders and arms
and bones of pelvis and legs
appendix- add-on, extra

4. Composition of Bone Non-living: 2/3 mass of bones is minerals
Calcium and phosphate mainly
protein fiber
But also fluoride, Na+, magnesium, calcium carbonate
these crystals are strong but brittle
cell
crystal
Living: 1/3 bone mass is protein fibers (collagen) and bone cells
Protein fibers are produced first and crystals are packed around the fibers, cells found in between strands
The combination (fibers + crystals) gives the bone both strength and some flexibility

5. Bone cells – 4 types
1) Bone stem cells – can make new bone cells
2) Osteocytes – mature bone cells, maintain bone matrix
3) Osteoblasts – make new bone
4) Osteoclasts - destroy bone
Osteoblasts and osteoclasts together remodel bones

6. Femur Two types of bone, both found in most bones Red marrow
Periosteum
shaft
Yellow marrow

7. Red and yellow bone marrow
Spongy bone under microscope

8. Compact bone still has cells in it
They need nutrients (name 2) from the blood
So compact bone has tubes called Haversian canals that run through the bone

9. These canals contain blood vessels and sensory neurons
So if you break a bone –
it bleeds!
it hurts!

10. Exercise Bones remodel in response to stress (weight/ pressure)
Weight-bearing exercise stresses bones, they respond by building more mass
Conversely, absence of stress causes loss of bone mass
especially a problem in space - no gravity
long term astronauts may pass point of no return - bones too weak to live on Earth again