bone formation and repair

Question 1

ossification occurs in what 4 principle situations

Answer 1

1. Initially in embryo & foetus
2. Growth
3. Remodelling
4. Repair of fractures

Question 2

name the 2 bone formation mechanisms

Answer 2

Intramembranous ossification

Endochondral ossification

Question 3

describe the bone formation mechanism Intramembranous ossification

Answer 3

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

Question 4

what does ossification basically mean

Answer 4

laying down of bone tissue

Question 5

describe the bone formation mechanism endochondral ossification

Answer 5

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

Question 6

describe step 1 of intramembranous ossification

Answer 6

Development of ossification centre:

• Mesenchyme cells differentiate=> osteogenic=> osteoblasts
• Osteoblasts can secrete organic matrix

Question 7

describe step 2 of intramembranous ossification

Answer 7

Calcification- cells become osteocytes:

• In lacunae they extend cytoplasmic processes to each other
• Deposit calcium & other mineral salts

Question 8

describe step 3 of intramembranous ossification

Answer 8

Formation of trabeculae- spongy bone:

• Blood vessels grow in and red marrow is formed (as this is found in flat bones mostly)

Question 9

describe step 4 of intramembranous ossification

Answer 9

Mesenchyme condenses at periphery => periosteum

E.g. flat bones of skull and mandible

Question 10

describe step 1 of endochondral ossification

Answer 10

Develop a cartilage model – where mesenchyme cells crowd together in shape of bone -> chondroblasts

Question 11

describe step 2 of endochondral ossification

Answer 11

Growth: - chondroblasts secrete cartilage

• Perichondrium forms on surface
• Internal chondrocytes in lacunae die (as cartilage isn’t needed anymore) and form small cavities

Question 12

describe step 3 of endochondral ossification

Answer 12

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

Question 13

describe step 4 of endochondral ossification

Answer 13

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

Question 14

describe step 5 of endochondral ossification

Answer 14

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

Question 15

explain bone growth in terms of length, ageing, etc

Answer 15

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

Question 16

name the zones of the epiphyseal plate

Answer 16

proliferative zone

hypertrophic cartilage zone

zone of calcification,

zone of ossification

Question 17

what do the zones of the epiphyseal plate do together

Answer 17

These zones work together to increase the length of the bones

Question 18

explain the proliferative zone of the Epiphyseal Plate

Answer 18

chondrocytes divide rapidly and form columns of stacked cells parallel to the axis of the bone.

Question 19

explain the hypertrophic cartilage zone of the Epiphyseal Plate

Answer 19

contains chondrocytes (and their lacunae) that have enlarged.

Question 20

explain the zone of calcification, of the Epiphyseal Plate

Answer 20

chondrocytes die leaving large empty holes.

As they die, Osteoblasts and blood vessels invade the area and begin secreting bone matrix.

Question 21

explain the zone of ossification of the Epiphyseal Plate

Answer 21

In the zone of ossification, bone matrix, is formed.

Question 22

bone remodelling occurs in response to use……

Answer 22

resorption by osteoclasts and deposition by osteoblasts

Question 23

describe the process of repair of bone after a fracture

Answer 23

1. Dead tissue removed
2. Chondroblasts => fibrocartilage (strongest extracellular material in the body)
3. => spongy bone formed by osteoblasts
4. => this will be remodelled to compact bone

Question 24

name and describe the types of fracture

Answer 24

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

Question 25

explain the factors affecting bone growth in terms of food consumption

Answer 25

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.

Question 26

what disease in the body can occur due to a lack of vitamin D

Answer 26

rickets

Question 27

name 2 other factors affecting growth apart from nutrition

Answer 27

hormones
weight bearing exercise

Question 28

explain how hormones can impact on growth

Answer 28

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.

Question 29

explain the effects of exercise on bone tissue

Answer 29

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.

Question 30

explain how ageing (from birth to elderly) affects bone development

Answer 30

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.