Bone and Ossification Flashcards
What are some characteristics of bone?
- can withstand compression, stress and deformation
- dynamic
- vascular (blood and lymph vessels supplied)
- sensitive to pain, especially in periosteum
What are the functions of bone?
Support, protection, mineral storage, haemopoiesis.
What is the composition of the bone matrix?
- It is 65% inorganic (calcium phosphate, calcium carbonate etc)
- it is 35% organic (collagen, water, 2% non collagen)
What causes bone to be hard?
Hardness and rigidity is due to interaction between inorganic salts and collagen. Flexibility is due to collagen.
Where are the calcium and phosphate stored?
Either in matrix or released into blood to maintain proper level
What is the effect of parathyroid hormone on bone?
Parathyroid hormone stimulates the osteoclasts to break down bone matrix leading to calcium in the blood. When blood calcium levels are higher than normal calcitonin is released, which inhibits osteoclast activity and decreases bone reabsorption.
Which type of cells do osteogenitor cells become?
Osteoblasts
What is the function of osteoblasts?
They synthesise organic components of cells making bone. They produce osteoid matrix.
What is the function of osteocytes and where are they found?
They’re found embedded within lacunae cavities. They are entombed osteoblasts. They maintain the bone matrix.
What are osteoclasts?
They are large multinucleated cells, formed from monocytes, that digest bone
What is the structure of compact bone?
Concentric Iamellae with central microvascular (haversian) canal, which communicate via Volkmann’s canals. The Haversian system is a system of interconnecting canals present in compact bone.
What is the structure of spongy bone?
It is a meshwork of trabeculae filled in with marrow.
What is the function of red bone marrow?
Red blood cell synthesis
What is the function of yellow bone marrow?
Contains adipose tissue
What is the marrow lined with?
Endosteum
What is the primary microstructure of bone?
It is woven/immature born that will eventually be replaced by mature bone. Collagen fibres arranged randomly. More cells and less minerals
What is the secondary microstructure of bone?
Series of Haversian systems consisting of concentric lamellae of bone laid around central canal containing blood vessels. Spaces between haversian systems are interstitial lamellae and whole bone surrounded by circumferential lamellae
Which types of bones are formed via endochondral ossification?
Long bones
Which types of bones are formed via intramembranous ossification?
Flat bones develop by intramembranous ossification, examples being:
- skull bones
- maxilla
- mandible
- pelvis
- clavicle
Describe the condition of Osteogenesis Imperfecta
- Autosomal Dominant disease resulting in type 1 collagen deformity/deficiency, major component in ground substance of bone.
- Brittle bone disease
- Most severe case leads to no conversion of feotal (hyaline) skeleton, incompatible with life. In most cases, repeated fractures lead to bowed long bones.
- Blue sclera due to unknown cause, possibly thinning of cornea due to issues with collagen that forms it.
Describe the condition of Rickets disease
- Deficiency in vitamin D
- less absorption of Ca2+ by small bowel -> less rigid bones. -bowed bones in children as they’re still growing.
- more common in dark skinned people as fair skin synthesises vit D better than dark skin.
Describe the condition of osteoporosis
Type 1 (menopausal) due to oestrogen no longer mediating osteoclast function – 2x more likely to fracture hip and 8x more likely to fracture vertebrae.
Type 2 (old age) due to loss of osteoblast function – no remodelling. Both due to clast > blast action.
Bone density decreases to the point of fracture risk. Medullar canals in centre of bone become enlarged and gaps develop in lamellae.
Describe the condition of osteomalasia
- Deficiency in vitamin D
- less absorption of Ca2+ by small bowel -> less rigid bones.
- bone/back ache, and can be secondary to impaired hepatic/renal function (less absorption).
- more common in dark skinned people as fair skin synthesises vit D better than dark skin.
What is the relavance of Vitamin D to bone development?
- precursor for calcitriol
- D3 absorbed from sunlight
- essential for calcium and phosphate absorption in small intestine
- in its absence, unclassified matrix is formed
- osteoblasts don’t become osteoclasts
