Skeletal system Flashcards
Describe the 6 steps of endochondral ossification
- Cartilage
stem cells form chondrocytes -> make cartilage - Growth of cartilage
cells in centre burst causing pH shift, triggering calcification - primary ossification centre
nutrient artery penetrates centre of cartilage - medullary cavity
bone mineral is reshaped + remodelled to form medullary cavity - secondary ossification centre
blood vessels enter the epiphyses (around time of birth) - formation of cartilage on the joints
cartilage on ends of bone remain as articular cartilage
Describe how long bones get longer
- growth plate forms new cartilage which becomes bone in the metaphysis, making the bone longer
- cartilage cells are produced by mitosis on epiphyseal side of plate
- cartilage cells are destrpoyed and replaced by bone on diphyseal side of plate
State what the growth of flat bones is called and how it occurs
Intermembranous ossification
- occurs when bones form directly from osteoblasts and do not have a growth plate or cartilage stage
-> fibroblasts differentiate into the osteoblasts and mineralise
State the components of bone
Organic collagen matrix (10%) -> flexibility
Mineral (65%) -> hydroxyapatite = insoluble salt of calcium + phosphorus
Water (25%)
Trace amounts of magnesium, sodium + bicarbonate
List the characteristics of osteoblasts
- matrix formation
- secrete type 1 collagen
- regulates mineralisation
- positioned above osteoid matrix
Differentiates to become osteocyte or undergoes apoptosis
List the characteristics of osteoclasts
- digests bone
- large + multi nucleated
- high density of golgi stacks, mitochondria + lysosomal vesicles
- undergo apoptosis once finished
List the characteristics of osteocytes
- born from osteoblasts
- maintains bone matrix
- occupies lacunae
- extends filpodia through canaliculi
forms gap junctions w/ neighbouring cells
List the characteristics of bone lining cells
- flat, elongated cells
- generally inactive
- cover surfaces of inactive bone
- thought to be precursor cells to osteoblasts
What are the 4 reasons bone remodelling is necessary
- to repair micro fractures
- to heal major fractures
- to adapt the skeleton to the demands of the structure
- to supply mineral as required for maintaining homeostasis
Describe the process and function of calcium homeostasis
- calcium is reabsorbed when kidneys filter blood
-> enables bone turnover / takes calcium from blood to go to bone
regulated by endocrine system
Describe the function of parathyroid hormone (PTH)
- produced by parathoid glands
- released in response to low blood calcium levels
-> increases bone resorption
Describe the function of calcitriol (active vitamin D)
- produced from cholseterol derived precursors + enzymatic steps in liver + kidney
- synthesised in response to high PTH levels
->increases bone resorption - regulates osteoblast + osteoclast function
Describe the effects of osteoporosis
- holes in bone become larger + are filled w/ fat or bone marrow
-> decreases density of bone - caused by imbalance of bone resorption + formation
results in fewer or thinner trabeculae
low bone mass
thin cortical bone
State the hormone released when blood calcium levels increase and the effects of this hormone
Calcitonin
Increased excretion of calcium by kidneys
increased calcium deposition in bones
Name a drug that inhibits bone resorption
Bisphosphonates
