CHAPTER 6- BONES AND SKELETAL TISSUE PT 2

Question 1

2 types of ossification (bone formation)

Answer 1

1. Intramembranous ossification (within fibrous membrane)
2. Endochondral ossification (“bone chases cartilage”)

Question 2

Intramembranous ossification

Answer 2

• growth within fibrous membrane, bone will start growing
• bone develops from fibrous membrane
• forms most flat bones (cranial bones, for example)

Question 3

Endochondral ossification

Answer 3

*within cartilage, bone chases cartilage
- cartilage (endochondral) bone forms by replacing hyaline cartilage model
- forms most of the rest of the skeleton
- requires breakdown of hyaline cartilage PRIOR to ossification

Question 4

Endochondral ossification steps

Answer 4

1. Bone collar starts to form around diaphysis
2. Medullary cavity starts to form inside bone collar
3. Blood vessels move into medullary cavity
4. Diaphysis elongates then the secondary ossification centers form in epiphyses (both ends of bones)
5. The epiphyses ossify (turn into bone)

Question 5

postnatal bone growth

Answer 5

1. interstitial growth
   - length of long bones (growth between cartilage lacuna)
2. appositional growth
   - thickness and remodeling of all bones by osteoblasts and osteoclasts on bone surfaces

Question 6

Bone resorption

Answer 6

*Taking away bone
osteoclasts secrete:
1. lysosomal enzymes (digest organic (osteoids and proteins) matrix)
2. acids (convert calcium salt into soluble forms)
- dissolved matrix is transcytoses across osteoclast, enters interstitial fluid and then blood

Question 7

Bone remodelling

Answer 7

1. resorption (removal) and deposit occur together
2. occurs at the surface of periosteum and endosteum
   
   • performed by osteoclasts (resorption) and osteoblasts (deposit)

Question 8

Bone remodeling

Answer 8

• resorption (removal) and deposit occurring together
• occurs at bone surface of periosteum and endosteum
  *performed by osteoclasts (resorption) and osteoblasts (deposit)

Question 9

Bone remodeling doesn’t…

Answer 9

happen equally throughout the skeleton
- areas of high stress (like neck of femur) remodel more to prevent becoming too brittle

Question 10

osteocytes are like the…

Answer 10

bosses of osteoclasts and osteoblasts, telling them to remodel

Question 11

Control of remodeling

Answer 11

1. hormonal mechanisms that maintain calcium homeostasis in the blood (for ions)
2. Mechanical and gravitational forces sensed by osteocytes:
   
   • communicate over large distances to stimulate remodeling

Question 12

removal of osteocytes causes…

Answer 12

loss of remodeling activities

Question 13

hormonal control of blood Ca2+

Answer 13

since most of the calcium in the body is stored in bone, calcium is necessary for:
- transmission of nerve impulses
- muscle contraction (in heart!)
- primarily controlled by parathyroid hormone (PTH)

Question 14

PTH process

Answer 14

1. Blood calcium levels drop (due to lots of exercise, for example)
2. Parathyroid glands increase release of PTH
3. PTH stimulates osteoclasts to resorb bone matrix and release calcium
4. Blood calcium levels increase
5. Parathyroid gland turns of influx of PTH
   ***NEGATIVE FEEDBACK LOOP (GOING BACK TO HOMEOSTASIS)

Question 15

Response to mechanical stress:

Answer 15

• Wolff’s Law: a bone grows/remodels in response to forces or demands placed upon it
• observations supporting Wolff’s Law:
  
  • handedness results in that hand’s bone being stronger and thicker
  • curved bones are thickest where they are most likely to buckle
  • trabeculae form along lines of stress
  • large, bone (tubercles and trochanters) projections occur where heavy, active muscles attach

Question 16

statistics

Answer 16

1. fractures of extremities are most common
2. more common in men up to 45 years of age
3. more common in women over 45 years of age
4. up to 75 years, wrist fractures most common
5. after 75 years, hip fractures most common

Question 17

Classification of bone fractures:

Answer 17

1. position of bone ends after fracture
   
   • nondisplaced: ends retain normal position
   • displaced: ends out of normal position
2. completion of the break (self explanatory)
3. orientation of the break to the long axis of the bone
   
   • linear: parallel to long axis of the bone
   • transverse: perpendicular to long axis of the bone
   • spiral or oblique: on an oblique angle (paper towel roll)
4. whether or not the bone ends penetrate the skin
   
   • compound (open): bone penetrates skin
   • simple (closed): bone ends don’t penetrate skin

Question 18

Common types of fractures:

Answer 18

1. Comminuted fracture
2. Compression fractures
3. Spiral or oblique
4. Epiphyseal fracture
5. Depression fracture
6. Greenstick
7. Transverse

Question 19

Comminuted fracture

Answer 19

3 or more bone pieces broken
High energy trauma

Question 20

Compression fracture

Answer 20

AKA Crush fracture (mostly vertabrae)
Fracture in spongy bone (result of compression- osteoporosis)

Question 21

Spiral or oblique

Answer 21

Caused by violence transmitted through limb from a distance (twisting movements)

Like twisting arm from wrist

Question 22

Epiphyseal fracture

Answer 22

Breakage at the growth plate

Question 23

Depression fracture

Answer 23

Broken bone portion is pressed inward (most common on the skull)

Question 24

Greenstick fracture

Answer 24

*mostly younger kids
Bone is broken incompletely (bone is bent without being completely broken)

Question 25

Transverse fracture

Answer 25

perpendicular to the fracture

Question 26

Functions of the x-ray

Answer 26

1. localizes fracture and possible fragments 2. indicates degree of displacement 3. evidence of pre-existing bone disease 4. foreign bodies or air in tissues, show other fractures * need MRI, CT or ultrasound to reveal soft tissue damage

Question 27

How to handle a fracture

Answer 27

1. Reduction: putting bone ends in right position - closed reduction: manipulation (cracking bone back into place w/o surgery) - open reduction (surgery): allows accurate reduction, risk of infection 2. manipulation: usually with anesthesia 3. traction fractures or dislocation requiring slow pulling resistance

Question 28

Steps in bone repair: Step 1

Answer 28

Hematoma (blood clot) forms: - torn blood vessels hemorrhage (because breaking bone tears blood vessels) - clot forms - inflammation site lasts 6-8 hours after surgery

Question 29

Steps in bone repair: Step 2

Answer 29

Fibrocartilaginous (soft) callus forms: *bone has to be fixed first - phagocytic cells clear debris - osteoblasts begin forming spongy bone within 1 week - fibroblasts secrete collagen fibers to connect bone ends - most of repair tissue now called soft callus (because it's not strong, just spongy bone) - lasts about 3 weeks

Question 30

Steps in bone repair: Step 3

Answer 30

Bony (hard) callus formation: - new trabecular form a bone (hard) callus - bony callus formation continues until firm union is formed in about 2 months *important to start using the bone

Question 31

Steps in bone repair: Step 4

Answer 31

Bone remodeling: - replacing trabeculae with osteons, compact bone

Question 32

Osteoporosis

Answer 32

* in vertebrae and neck of femur - loss of bone mass- bone resorption outpaces deposit - due to lack of estrogen, calcium or vitamin D