Skeletal and Muscular System

Functions of Skeletal System

5) Leverage - produces movements with skeletal muscles

4) Blood cell production - blood cells made here, in red marrow in the ends of bones

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

2) Protection - delicate organs surrounded or cradled by bony parts

1) Support - keep body upright, support organs, tissues

Skeleton

206 bones in human body6 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 legsappendix- add-on, extra

Composition of Bone

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 strandsThe combination (fibers + crystals) gives the bone both strength and some flexibility

Non-living: 2/3 mass of bones is mineralsCalcium and phosphate mainly

But also fluoride, Na+, magnesium, calcium carbonatethese crystals are strong but brittle

cell

protein fiber

crystal

Bone cells – 4 types

2) Osteocytes – mature bone cells, maintain bone matrix

3) Osteoblasts – make new bone

4) Osteoclasts - destroy bone

1) Bone stem cells – can make new bone cells

Osteoblasts and osteoclasts together remodel bones

Two types of bone, both found in most bones

Femur

shaf

t

Yellow marrow

Red marrow

Periosteum

http://medlib.med.utah.edu/WebPath/BONEHTML/BONEIDX.html

Red and yellow bone marrow

Spongy bone under microscope

Compact bone still has cells in itThey need nutrients (name 2) from the blood

So compact bone has tubes called Haversian canals that run through the bone

http://instruct1.cit.cornell.edu/courses/biog105/images/105slides/Unit10/index10.htm

http://instruct1.cit.cornell.edu/courses/biog105/images/105slides/Unit10/index10.htm

So if you break a bone – it bleeds!

it hurts!

These canals contain blood vessels and sensory neurons

Exercise

especially a problem in space - no gravitylong term astronauts may pass point of no return

- bones too weak to live on Earth again

Conversely, absence of stress causes loss of bone mass

Weight-bearing exercise stresses bones, they respond by building more mass

Bones remodel in response to stress (weight/ pressure)