Bone formation & Repair 20

Question 1

What are the 4 principal situations ossification occurs in?

Answer 1

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

Question 2

What are the 2 bone formation mechanisms?

Answer 2

1) Intramembranous ossification (simplest)
2) Endochondral ossification.

Question 3

Explain intramembranous ossification.

Answer 3

Simplest. Bone forms directly in mesenchyme layers ( membrane like). Mesenchyme (one of embryonic tissue layers) model is replaced with bone.

Question 4

Explain endochondral ossification.

Answer 4

Forms within hyaline cartilage developed from mesenchyme.

Question 5

Name & describe stage 1 of Intramembranous Ossification.

Answer 5

‘Development of ossification centre’. Where mesenchyme cells differentiate becoming osteogenic, further becoming osteoblasts which secrete organic matrix.

Question 6

Name & describe stage 2 of intramembranous ossification.

Answer 6

‘Calcification- cells become osteocytes’ In lacunae they extend cytoplasmic processes to each other. Deposits calcium & other minerals.

Question 7

Name & describe stage 3 of intramembranous ossification.

Answer 7

‘Formation of Trabeculae’ - spongy bone tissue. Blood vessels grow in & red marrow is formed.

Question 8

Name & describe stage 4 of intramembranous ossification.

Answer 8

‘Development of the periosteum’, Mesenchyme condenses at periphery’ - becoming periosteum. EG flat bones of skull and mandible.

Question 9

Name & describe stage 1 of endochondral ossification.

Answer 9

Develop a cartilage model - mesenchyme cells crowd together in shape of bone, called chondroblasts.

Question 10

What is the name of mesenchyme cells crowded together in the shape of a bone?

Answer 10

Chondroblasts.

Question 11

Name & describe stage 2 of endochondral ossification.

Answer 11

‘Growth” - chondroblasts secrete cartilage.
Perichondrium forms on surface of chondrobasts.
Internal chondrocytes in lacunae die and form small cavities.

Question 12

Name & describe stage 3 of endochondral ossification. (long answer, take notes)

Answer 12

‘Development of primary ossification centre’ - Ossification proceeds inwards with nutrient artery from surface perichondrium.
In disintegrating cartilage osteogenic cells = osteoblasts creating a ‘primary ossification centre’.
As bone forms perichondrium = periosteum.
First spongy bone is formed.

Question 13

Name & describe stage 4 of endochondral ossification.

Answer 13

‘Development of the medullary (marrow) cavity’.
osteoblasts break some bone down, developing a medullary cavity in centre of bone.
Outer wall of diaphysis = compact bone.

Question 14

Describe stage 5 of endochondral ossification.

Answer 14

Near birth, blood vessels enter epiphysis, developing secondary ossification centre. Hyaline cartilage at end of bone > articular cartilage. Prior to adulthood, hyaline remains in epiphyseal plates to allow bones to grow.

Question 15

What happens to hyaline cartilage before adulthood?

Answer 15

It remains in the epiphyseal plates to allow growth in bone length.

Question 16

Explain growth of bones before adulthood.

Answer 16

Chondrocytes in the epiphyseal plate divide and increase the cartilage layer. Later dying on the diaphysial side being replaced by bone.
Periosteum supports surface growth for thickness.

Question 17

Name the 4 zones of the epiphyseal plate.

Answer 17

Proliferation zone
Hypertrophic zone
Calcification zone
Ossification zone

Question 18

What happens at the proliferation zone in the epiphyseal plate?

Answer 18

Chondrocytes divide rapidly (mitosis) forming columns of stacked cells parallel to the axis of the bone.

Question 19

What happens at the hypertrophic zone in the epiphyseal plate?

Answer 19

Older chondrocytes and their lacunae enlarge.

Question 20

What happens at the calcification zone in the epiphyseal plate?

Answer 20

Matrix becomes calcified, begins deteriorating, chondrocytes die, leaving behind large empty holes.

Question 21

What happens at the ossification zone in the epiphyseal plate?

Answer 21

The bone matrix is formed.

Question 22

When bones are remodelled, they are reabsorbed by what cell?

Answer 22

Osteoclasts.

Question 23

When bones are remodelled, they are dispositioned by what cell?

Answer 23

Osteoblasts.

Question 24

What are the steps to repair a fracture?

Answer 24

1) Dead tissue is removed
2) Chondroblasts become fibrocartilage…
3) > spongy bone by osteoblasts
4) >remodelled to compact bone

Question 25

What are the types of fractures?

Answer 25

Partial/greenstick -incomplete break, children (crack)
Complete- bone in two or more pieces
Closed (simple)- not through skin
Open (compound)- broken ends break skin
Transverse, spiral, comminuted, vertebral, compression- elderly

Question 26

Describe osteoporosis.

Answer 26

Bones become brittle and lose calcium. Mainly occurs after menopause & men after 60.