bone formation and repair Flashcards
ossification occurs in what 4 principle situations
- Initially in embryo & foetus
- Growth
- Remodelling
- Repair of fractures
name the 2 bone formation mechanisms
Intramembranous ossification
Endochondral ossification
describe the bone formation mechanism Intramembranous ossification
This process forms a flat bone
simplest
Bone forms directly in mesenchyme layers (membrane like)
- Mesenchyme (one of embryonic tissue layers) model - replaced with bone
what does ossification basically mean
laying down of bone tissue
describe the bone formation mechanism endochondral ossification
forms within hyaline cartilage developed from mesenchyme
This process forms a long bone or cube shaped bone
Calcium starts to move in as the bone matures
describe step 1 of intramembranous ossification
Development of ossification centre:
- Mesenchyme cells differentiate=> osteogenic=> osteoblasts
- Osteoblasts can secrete organic matrix
describe step 2 of intramembranous ossification
Calcification- cells become osteocytes:
- In lacunae they extend cytoplasmic processes to each other
- Deposit calcium & other mineral salts
describe step 3 of intramembranous ossification
Formation of trabeculae- spongy bone:
- Blood vessels grow in and red marrow is formed (as this is found in flat bones mostly)
describe step 4 of intramembranous ossification
Mesenchyme condenses at periphery => periosteum
E.g. flat bones of skull and mandible
describe step 1 of endochondral ossification
Develop a cartilage model – where mesenchyme cells crowd together in shape of bone -> chondroblasts
describe step 2 of endochondral ossification
Growth: - chondroblasts secrete cartilage
- Perichondrium forms on surface
- Internal chondrocytes in lacunae die (as cartilage isn’t needed anymore) and form small cavities
describe step 3 of endochondral ossification
Ossification proceeds inward with nutrient artery from surface perichondrium
- In disintegrating cartilage osteogenic cells=> osteoblasts and create a primary ossification centre
- As bone forms perichondrium => periosteum (more fibrous layer of tissue)
- First spongy bone is formed
describe step 4 of endochondral ossification
Osteoblasts break some of bone down =>
- Centre develops a medullary cavity (where the matric will fill up with yellow fat)
- wall of diaphysis => compact bone
More compact structure start to form here
describe step 5 of endochondral ossification
Once Near birth, blood vessels enter epiphysis:
- Secondary centre is developed:
- Hyaline cartilage at end of bone => articular cartilage
- Prior to adulthood hyaline cartilage remains in the epiphyseal plates -> growth in bone length
explain bone growth in terms of length, ageing, etc
Length - chondrocytes in the epiphyseal plate divide and increase cartilage layer
On diaphyseal side (closer to inside of bone) they die and are replaced by bone
Stops during adolescence as we no longer grow
Periosteum supports surface growth for thickness
name the zones of the epiphyseal plate
proliferative zone
hypertrophic cartilage zone
zone of calcification,
zone of ossification
what do the zones of the epiphyseal plate do together
These zones work together to increase the length of the bones
explain the proliferative zone of the Epiphyseal Plate
chondrocytes divide rapidly and form columns of stacked cells parallel to the axis of the bone.
explain the hypertrophic cartilage zone of the Epiphyseal Plate
contains chondrocytes (and their lacunae) that have enlarged.
explain the zone of calcification, of the Epiphyseal Plate
chondrocytes die leaving large empty holes.
As they die, Osteoblasts and blood vessels invade the area and begin secreting bone matrix.
explain the zone of ossification of the Epiphyseal Plate
In the zone of ossification, bone matrix, is formed.
bone remodelling occurs in response to use……
resorption by osteoclasts and deposition by osteoblasts
describe the process of repair of bone after a fracture
- Dead tissue removed
- Chondroblasts => fibrocartilage (strongest extracellular material in the body)
- => spongy bone formed by osteoblasts
- => this will be remodelled to compact bone
name and describe the types of fracture
Partial- incomplete break (crack) - greenstick - common in children
Complete - bone in two or more pieces, these breaks can appear in different appearances:
- Transverse, spiral, comminuted, vertebral compression - common in elderly (Dowager’s hump)
Closed (simple)- not through skin
Open (compound)- broken ends break skin
explain the factors affecting bone growth in terms of food consumption
Adequate minerals (Ca, Mg, P)
Vitamins A, C, D
- Vitamin A – Yellow and orange fruits and vegetables, dark green leafy vegetables, whole eggs, whole milk, and liver
- Vitamin C – Citrus fruits, tomatoes, broccoli, green peppers, cantaloupe, and strawberries
- Vitamin D – Only a few foods naturally contain significant amounts of vitamin D, including fatty fish and fish oils. Milk is usually fortified with Vitamin D.
Exposure to sunlight is another source of vitamin D, but exposure to sun should be limited.
what disease in the body can occur due to a lack of vitamin D
rickets
name 2 other factors affecting growth apart from nutrition
hormones
weight bearing exercise
explain how hormones can impact on growth
Before puberty: human growth hormone (hGH) + insulin-like growth factors
Thyroid hormone & insulin also required
Sex steroids help adolescent growth spurt and cause closure of epiphyseal plate.
explain the effects of exercise on bone tissue
Bone is strengthened in response to use
It is reabsorbed during disuse
- e.g. Bone loss during bed rest, fractures in cast, astronauts with no gravity.
explain how ageing (from birth to elderly) affects bone development
Birth through adolescence more bone formed than lost
Young adults - gain & loss about equal amounts
As levels of sex steroids decline with age: bone resorption exceeds bone formation
Bones become brittle and lose calcium -> osteoporosis
Occurs after the menopause in women and in men from late sixties onwards.
