Bone Growth and Adaptation Flashcards
What is endochondral ossification?
- bone development from hyaline cartilage template
- forms most of the bones in the body
What is intramembranous ossification?
- bone development within fibrous connective tissue
- mesenchymal cells form osteoblasts and osteocytes
- forms mandible bones, flat bones of the skull
- also how endochondral bones increase thickness
- important in bone healing
What does physis and growth do?
- allows for continued longitudinal growth of bone
What are the layers of cartilage in endochonral ossification?
- reserve/ resting cartilage (normal cartilage)
- proliferating zones (cells dividing rapidly by mitosis)
- hypertrophic zone (alkaline phosphate section)
- calcification zone (cells dying)
- ossification zone ( invasion of vessels from medullary spaces bringing osteoblasts)
Describe the process of closing growth plates
- around puberty, new cartilage stops being made
- physis ossifies, uniting diaphysis and epiphysis
- no further longitudinal growth
- time of growth plate closure varies between physis, bone, species and breed
- the physis can sometimes still be visible as a line
What does endochondral ossification do?
- allows longitudinal growth in bones
What does intramembranous ossification do?
- allows circumferential growth of bone
- osteoblast in the periosteum deposit bone around periosteal vessels
- new layers of bone added on outer surface
what in combination creates an increase in bone circumference?
- periosteal new bone formation (osteoblasts)
- endosteal bone reabsorption (osteoclasts)
Bone can be classified by the arrangement of what?
- collagen fibres in the matrix
What is lamellar bone?
- collagen fibres organised in parallel layers
- dense (stronger)
- typical of normal adult skeletal structure
What is woven bone?
- irregular collagen fibres
- more cellular
- weaker
- seen in rapid growth such as growing animals, fracture healing
- usually later replaced by lamellar bone
How are calcium and phosphate acquired?
- through diet
How are calcium and phosphate filtered?
- filtered by the kidney and reabsorbed before lost in urine
Where are calcium and phosphate stored?
- stored in bone
- 99% of calcium
- 85% of phosphate
What is calcitriol?
- calcitriol is a hormone, and the active form of vitamin D
What does calcitriol act to do?
- increase calcium and phosphate absorption from the small intestine
- enhance reabsorption of calcium and phosphate by kidney
- stimulates release of calcium from bones
What does parathyroid hormone (PTH) do?
- increases reabsorption of of calcium from kidney
- reduce reabsorption of phosphate from kidney
- increases conversion of vitamin D to calcitriol
When is PTH released?
- when blood calcium levels fall
When is calcitonin released?
- when blood calcium levels rise
What does calcitonin do?
- inhibits reabsorption of calcium from bone (osteoclasts)
- inhibits reabsorption of calcium and phosphate from kidney
What does growth hormone do?
- stimulates bone turnover
What does sex hormones oestrogen and testosterone do in bones?
- inhibits bone reabsorption
- affect physis closure
What does Glucocorticoids do?
- inhibit osteoblasts (bone loss)
What does TH (thyroid hormone) do?
- increased reabsorption of bone
