Skeletal System Flashcards
Lec 16
What are the fxns of the skeletal system?
- structural support 2. protection of vital organs 3. attaches mms to allow for mvmt 4. red marrow produces all blood cells 5. stores Ca2+
When does bone ossification begin?
begins at around 8th week –> around 20 yrs
What is a skeleton of an embryo formed of in first 8 weeks?
constructed of fibrous membranes and hyaline cartilage. add minerals to these to ossify.
What are the two types of bone ossification?
- intramembranous ossification 2. endochondral ossification
What happens during intramembranous ossification and in what bones?
in flat bones ie some skull bones, clavicle, and mandible. develop form fibrous connective tissue membrane where a mineral component is added. process; osteoblasts produce spongy bone along the connective tissue fibres, and cells at the periphery form the periosteum (surrounds/covers bones) and the osteoblasts underneath it lay down compact bone on the outside of the spongy bone. so building of bone goes from inside to outside.
What are fontanels?
unossified membranes in the skull that remain at birth to allow for mvmt.
What happens during endochondral ossification and in what bones?
most bones below skull. hyaline cartilage acts as a model for bone construction, then ossifies to form spongy bone. periosteum forms and the osteoblasts beneath it lay down compact bone. the articular cartilage and epiphyseal plates are the cartilage that has not ossified.
What are the different types of bone growth postnatal?
- growth in length - endochondral growth 2. growth in diameter - appositional growth
How does growth in length happen?
endochondral growth at epiphyseal plates using the cartilage template. process; cartilage grows and the matrix near the diaphysis becomes bone. growth in length stops when epiphyseal plate ossifies into epiphyseal line.
How does growth in diameter happen?
appositional growth happens by adding to outside of compact bone while th. inside is broken down. process; osteoblasts beneath the periosteum secrete bone matrix and then osteoclasts resorb bone on the endosteal surface therefore the size of the cavity keeps pace with growing bone.
What are the factors that affect bone growth/remodeling?
- mechanical stress 2. nutrition 3. hormones
How does mechanical stress affect bone?
happens usu due to mm action where stress on bones make them grow and get thicker. ex; moderate exercise; increases osteoblast activity in areas of stress (more building of bone then breaking down). injury that restricts mvmt; decreases osteoblast activity and no change in osteoclast activity causing a reduction on bone mass. weights or electric currents; may speed healing by increasing osteoblast activity.
How does nutrition affect bone?
a. Ca2+, PO4- - required for bone matrix production. b. vitamin C - required for collagen production c. vitamin D -increases absorption of Ca from intestine
What does a lack of vitamin D cause?
Rickets - soft bones in kids.
How do hormones affect bone?
a. growth hormone, thyroid both stimulate bone growth b. E and T - increase osteoblast activity, E causes ossification of epi plate c. calcitonin - inhibits osteoclast activity which increases Ca mvmt from blood into bone and promotes bone growth (decreases bl Ca). d. parathyroid hormone - increases osteoclast activity and decreases osteoblast activity. breakdown of bone release Ca into the blood
What is osteoperosis?
a bine disease characterized by a reduction in bone density and bone mass that leads to more fragile bones and increased risk of fracture.
What are the risk factors of osteoperosis?
- increasing age (decreased production of sex hormones ie T E and P) 2. post-menopuase - decreased E production 3. inadequate diet - decreased vit D, Ca 4. illness, excess PTH 5. too little/excessive exercise - stress, cortisol 6. drugs - cortisone and alcohol reduce osteoblast activity, smoking decreases E.
What is the process of bone repair?
- begins with formation of bl clot 2. replaced by callus - consists of fibrous network and fibrocartilage islets laid down 3. callus ossifies - intramembranous and endochondral ossification 4. takes 4-6 wks so cast required since mvmt can re-fracture new matrix.
