skeletal system

Question 1

functions

Answer 1

1. support
2. protection of vital organs
3. attaches muscle + allows movement
4. red marrow produces rbc, wbc
5. stores Ca++

Question 2

bones ossification

Answer 2

• before week 8, skeleton of embryo constructed of fibrous membranes + hyaline cartilage
• bone formation begins at ~8th week - 20 years

Question 3

what are the types of bone ossification

Answer 3

1. intramembranous ossification
   - flat bones
   - develop from fibrous CT
2. endochondral ossification (most bones)
   - hyaline cartilage used as a model for bone construction - then ossifies to form spongy bone.
   - periosteum forms and the osteoblasts beneath lay down compact bone

Question 4

what is the process of intramembranous ossification

Answer 4

• osteoblasts produce spongy bone along CT fibres
• periosteum forms and then osteoblasts under it lay down compact bone
• frontanels = unossified membranes in the skull that remain at birth

Question 5

bone growth (postnatal)

Answer 5

1. growth in length
   - endochondral growth at epiphyseal plate
2. growth in diameter
   - appositional growth

Question 6

what is the process of growth in length

Answer 6

• cartilage grows - matrix near diaphysis becomes bone

- growth in length stops when epiphyseal plate ossifies into epiphyseal line

Question 7

what is the process of growth in diameter

Answer 7

• osteoblasts beneath periosteum secrete bone matrix (external bone surface)
• osteoclasts resorb bone on the endoseal surface

Question 8

factors affecting bone growth/remodelling

Answer 8

1. mechanical stress
   - due to muscle action
2. nutrition
   - Ca, PO4 for production of bond matrix
   - lacking vitamin D, rickets in children
3. hormones
   - growth hormone, thyroid hormone stim. bone growth
   - estrogen + testosterone increases osteoblast activity

Question 9

osteoporosis

Answer 9

• lowers bone mass
• risk factors:
  1. increasing age
  2. post-menopause
  3. inadequate diet
  4. illness, excess PTH
  5. too little/excessive exercise (stress-cortisol)
  6. drugs e.g. cortisone, alcohol which lowers osteoblast activity

Question 10

bone repair process

Answer 10

1. begins with formation of a blood clot
2. clot replaced by a callus - consists of fibrous network + fibrocartilage islets
3. callus ossifies - intramembranous +endochondral ossification
4. takes 4-6 weeks - cast required since movement can re-fracture new matrix.