Bone Flashcards
what tissue does bone originate from
- mesenchyme
what is the first bone to ossify/when
- the clavicle
- 6 weeks gestation
define osteocyte
mature bone cell that turns over bone mineral and assists in repair
define osteoblast
- immature bone cell that secretes organic matrix
define osteoprogenitor cell
- stem cell that divides to produce osteoblasts
define osteoclast
- multinucleated cell that secretes acids/enzymes to dissolve bone matrix
outline the steps of intramembranous ossification
- cells unite in center of mesenchyme and form the blastemal
- osteogenic cells then become osteoblasts
osteoblasts lay down ossified tissue matrix - osteoblasts get caught in lacunae and become mature osteocytes
What types of bones grow intramembranously
- flate bones: bones of the skull, scapula
Describe the two ways in which the skull grows in childhood
- appositional/depositional growth via osteoblasts on the outer surface causes a lateral & outward expansion.
- Reabsorption by osteoclasts enlarges the internal cavity making room for the growing brain
What bone utilizes both endochondrial and intramembranous growth?
the jaw
What is the result of too much growth hormone before vs after puberty?
- before: Increase in height with normal proportions
- after: thickening of bone and overgrowth of connective tissue
what are the steps involved with endochondral ossification
- mesenchymal clump > cartilaginous model
- osteoblasts begin ossification from the center of the cartilaginous model and move outwards
- cartilage remains at articulating surfaces
give examples of endochondral ossification
- short bones: Carpals, tarsals
- Long bones: tibia, femur, humerus
Describe the 5 steps of long bone ossification
(a) Mesenchymal cells differentiate into chondrocytes. (b) The cartilage model of the future bony skeleton and the perichondrium form. (c) Capillaries penetrate cartilage. Perichondrium transforms into periosteum. Periosteal collar develops. Primary ossification center develops. (d) Cartilage and chondrocytes continue to grow at ends of the bone. (e) Secondary ossification centers develop. (f) Cartilage remains at epiphyseal (growth) plate and at joint surface as articular cartilage.
what is the functional unit of bone
- osteon
where are osteocytes housed
lacunae
through what structure do osteocytes communicate
- canaliculi
at how many weeks of gestation would we see endochondral ossification begin
- 9 weeks
What two methods were developed to determine skeletal age
- Atlas method by Greulich and Pyle (American)
- TW2 method by tanner and whitehouse (british) (better reliability)
- Atlas will give a lower rating than TW2 for a given individual
What body part is used to study skeletal age most often; why?
- The hands
- There are many bones present therefore many ossification centres to look at
What happens to bone development if there’s a decrease in HGH and gonadotrophins; give an example
- delayed & stunted growth; will not reach full potential
- turner syndrome, 45 X0; deficiency in HGH and estrogen result in stunted growth and lack of female qualities
How does the environment affect bone
- Exposure to different stressors and strain modifies the shape, size and strength of bones
- These modifications follow mathematical laws
Simplified Wolff’s Law
- Relates to exercise and the impact of movement on bone
What are the effects of exercise on bone growth
- increased bone density
