Osseous Tissue and Bone Structure

6.1I. Intro to the skeletal system

A. includes the bones, cartilages, ligamentsB. Functions: five primary

1. support- provide framework for muscle attachment 2. Stores minerals & lipids

-bones store calcium and phosphate ions -store lipids in yellow marrow

3. produce blood cells- red marrow produces red and white blood cells4. protection

-protect soft tissues and organs- ribs protect heart and lungs

5. leverage-can change direction and amount of

force produced by muscles- allow for precise motion

6.2II. Bone classifications

A. Shapes-typical adult skeleton has 206 bones- divided into 6 shape based categories

1. long bones- long and slender- found in arm, forearm, thigh, leg,

fingers & toes -femur is the largest &heaviest bone in the body 2. flat bones- thin parallel surfaces

- form the roof of the skull, sternum, ribs-protect underlying soft tissues - attachment site for muscles

3. sutural bones- (Wormian bones)- small, flat, irregular shaped- in skull- jigsaw borders

4. irregular bones-complex shapes-short, flat, ridged surfaces- spinal vertebrae, some skull bones

5. short bones-small & boxy-wrist & ankle bones

6. sesamoid bones (shaped like sesame seed)- generally small, flat-develop inside tendons -located near joints-kneecap

B. Bone markings PAGE 187 -surface features

-grouped as projections, depressions, openings- can provide info like age, sex, size

1. elevations/projections-form where tendons and ligaments

attach -where bones join (joints)

2. depressions/grooves-form sites where blood vessels or nerves

lie along surface or go through bone

C. Bone structure1. parts of long bone

a. diaphysis- shaft, made of compact boneb. metaphyses- area between shaft and end

(epiphyses)c. epiphyses- expanded area at end of shaftd. medullary cavity- space in shaft for red or

yellow bone marrow2. bone tissue

a. compact tissue -relatively solid, dense -forms protective layer around medullary

cavityb. spongy bone (cancellous) -open network, porous -covered by thin covering of compact bone

(cortex)

6.3III. Bone Matrix and Cell types

Osseus tissue is a supporting connective tissue

Why? –specialized cells-matrix of extracellular protein

fibers & ground substance A. bone matrix

1. bone weight 2/3 from calcium phosphate 1/3 from collagen fibers 2% of mass contributed by cells

2. Calcium phosphate interacts w/ calcium hydroxide-forms hydroxyapatite crystals

3. Calcium crystals are hard but brittle-can tolerate compression-can’t tolerate twisting or sudden impact

4. Collagen fibers are very strong -provide framework for crystals to form on-are flexible, can bend-don’t resist compression

5. fibers &crystal combination allows bone to be strong, somewhat flexible, resistant to shattering

B. Cells in bone1. osteocytes-mature bone cells

- make up most of cell population-each occupies a lacuna, a pocket in layers

of matrix(lamellae)- can’t divide- rely on canaliculi (passageways through

lamellae) to connect lacunae w/ one another & nutrient source

- Functions: *create chemicals that dissolve matrix

& rebuild the matrix, stimulating deposition of crystals*can convert to other cell types in case

of bone injury (released from lacunae)

2. osteoblasts- produce new bone (process of osteogenesis)- make & release proteins for matrix- organic component of matrix is called osteoid- elevate calcium phosphate levels to trigger the deposit of salts- turn into osteocytes once surrounded by matrix3. osteoprogenitor cells- stem cells-divide to produce cells that become osteoblasts- maintain osteoblast populations- important in repairing fractures- located on outer surface of bone (periosteum) & inner layer lining medullary cavity (endosteum)

4. osteoclasts- remove recycle bone matrix- giant cells- 50+ nuclei-not related to other bone cells, but

come from stem cells that produce macrophages

-secrete enzymes that dissolve matrix and release stored minerals (osteolysis)

-helps to regulate calcium & phosphate concentrations in body fluids

5. balance bwtn osteoblasts & osteoclasts is important in maintaining bone health---too much osteoclast activity will weaken bones