Bone tissue part 3

What are the 2 types of ossification

intramembranous ossification and endochondral ossification

Intramembranous ossification and what does it form

membrane bones develop from fibrous membrane

forms flat bones (clavicle/ cranial)

What are the 4 steps of intramembranous ossification

1. ossification center appears in fibrous connective tissue

2. osteoblasts secrete osteoids and calficifies

3. trabeculae forms (woven bone)

4. compact bone and red marrow appears

Endochondral ossification and what bones does it form

cartilage (endochondral) bones form by replacing hyaline cartilage (breakdown)

forms most of rest of skeletons (not clavicles and skulls)

What are the 5 stages of endochondral ossifcation

1. Bone collar forms on hyaline cartilage model & cartilage calcifies

2. Periosteal bud enters → primary ossification center

3. diaphysis (shaft) ossifies and medullary cavity

4. second ossification center

5. epiphyses ossifies

where are the hyaline cartilage at the end of endochondral ossifcation

hyaline cartilage only in epiphyseal plate and articular cartilage

interstitial bone growth & what important structure is associated with it

grows length of long bone at epiphyseal plate (growth plate)

Appositional bone growth → how & what important structure

Grows width of all bones

thickness and remodeling by osteoblast and osteoclasts on bone surface

bone matrix secreted under periosteum

what bones grow only by interstitual growth

long bones → length

What do growth hormones do

stimulate epiphyseal plate from pituitary glands

Thyroid hormones

regulate growth hormone activity

What does testosterone and estrogen do and how does it end growth

Promote adolescent growth

Ends growth by causing the epiphyseal plate to close (18 and 21)

calcium and phosphate regulation - intestines

absorb Ca and Po4 from food → rate of absorbtion regulated by hormones

calcium and phosphate regulation - bones

osteoblasts store Ca2+ when secrete osteoid and osteoclasts release Ca2+ and PO4 3- into blood when resorbing osteoid

their activity is regulated by hormones

calcium and phosphate regulation - kidney

hormones regulate amount of ca2+ and PO4 3- lost by urine

When Blood Ca2+ level is low in blood

Parathyroid gland release parathyroid hormone → stimulate osteoclasts to degrade bone and release Ca2+ into blood

Wolff’s law

bones grow and remodel based on stress and mechanical tension on it

Displaced fracture

2 seperate bones

non displaced fracture

crack but don’t seperate

open fracture

breaks skin

closed

bone doesnt break skin

comminuted fracture

multiple fragments - shattered

spiral fracture

twsiting force

compression fracture

bones crushed - common in osteoporosis

depressed fracture

pushed inward

greenstick fracture

incomplete - one side breaks other side bends

traverse fracture

horizontal

linear fracture

vertical

oblique fracture

diagonal

What are the four stages of bone fractures

Hematoma, fibrocartilaginous callus, bony callus, remodeling

Hematoma stage of bone fracture healing

First stage - blood clot forms (hematoma) → site is swollen painful inflamed

Fibrocartilaginous callus stage of fracture healing

2nd stage

fibroblast secrete collage to connect bones

osteoblasts form spongy bones (1 week)

Bony callus stage of bone fracture healing

3rd stage → firm union (8 weeks)

Bone remodeling stage of fracture healing

4th stage - based on wolff’s law

Osteoporosis (osteopenia)

loss of bone mass because bone resorption is faster than bone deposit (building)

Most vulnerable bones to fracture because of osteoporosis

spongy bones of spine and femur

Risk factors of osteoporosis

Low calcium and vitamin d, low estrogen, immobility

diabetes low tsh

treatments for osteoporosis (osteopenia)

supplements, hormone replacement therapy, exercise, drugs for bone mineral density