MS Systems: Bones and Bone Growth

Question 1

What are the functions of bones?

Answer 1

\+ Protection
\+ Support
\+ Movement
\+ Storage of minerals (Ca, P, Mg)
\+ Blood cell formation

Question 2

What are the structural features of a long bone?

Answer 2

+Epiphysis (head)

+ Diaphysis (shaft)

+ Periosteum

Question 3

What are features of the Epiphysis?

Answer 3

+ Articular surface

+ Covered by hyaline cartilage

Question 4

What are features of the diaphysis?

Answer 4

+ Hollow cylinder
+ Contains bone marrow
+ Nutrient foramen

Question 5

What are features of the periosteum?

Answer 5

Fibrous layer that covers external surfaces. Cells include:

• fibroblasts: synthesize collagen
• mesenchymal cells: can differentiate into osteoblasts and chondroblasts
• osteoclasts

Question 6

What are the functions/features of osteoclasts?

Answer 6

+ Resorb bone matrix by demineralization in response to mechanical stresses and physiological demands

+ Multinucleated

+ Derived from haematopoietic cells

+ Regulated by osteoblasts and hormones

Question 7

How to osteoclasts resorb bone?

Answer 7

+ Form a “sealing zone” on bone

+ Release H+ and hydrolytic enzymes to dissolve the mineral, liberate calcium and break down the extracellular matrix

+ Regulated by osteoblasts and hormones

Question 8

What are the functions/features of osteoblasts?

Answer 8

+ Responsible for bone formation

+ Cuboidal cells, derived from osteoprogenitor cells that line the surface of the bone

+ Deposit the organic matrix, then cause mineralisation

+ Some become entombed during this process, mature into osteocytes

Question 9

What are the features/functions of osteocytes?

Answer 9

+ Mature bone cells; embedded in lacunae, relatively inactive

+ Maintain bone matrix through cell-cell communication: via projections in canaliculi

+ Influence bone remodelling

+ Mechanosensing

Question 10

What is the structure/function of compact bone?

Answer 10

+ Osteons or Haversian systems
+ Very strong, light cylinder that resists compressive (grav.) forces
+ Osteocytes buried alive in the bone matrix

Question 11

What is the structure of cancellous/trabecular bone?

Answer 11

+ Spongy, porous, bone tissue that is filled with red bone marrow

+ Not as strong as cortical bone found in long bones, but very important for producing blood cells

+ Found in ends of long bones and the pelvis, ribs, vertebrae, and skull

Question 12

What effect does calcitonin have on osteoclast activity and blood calcium levels?

Answer 12

It decreases the activity of osteoclasts, therefore decreasing blood Ca++ levels

Favours bone resorption/atrophy

Question 13

What effect does parathyroid hormone (PTH) have on osteoclast activity and blood calcium levels?

Answer 13

It increases the activity of osteoclasts and releases Ca++

Favours bone formation/hypertrophy

Question 14

What are the steps in the bone remodelling cycle?

Answer 14

+ Resorption
+ Reversal
+ Formation
+ Quiescence

Question 15

How can bone mass and density increase?

Answer 15

Excessive mechanical stimulation

Question 16

How can bone mass and density decrease?

Answer 16

+ Non-weight bearing (immobilisation)

+ Sex-hormone deficiency (e.g menopause)

+ Endocrine/nutritional disorders

Question 17

What is Wolff’s law?

Answer 17

+ Bone adapts to the load under which it is placed e.g orthodontic braces, head binding

Question 18

How long do fractures of woven bone take to heal?

Answer 18

2-4 weeks

- dependent on the severity and position of the fracture and age of the patient

Question 19

What are the steps of bone fracture healing?

Answer 19

+ Callus formation

• osteoblasts quickly form woven bone to bridge the gap
• woven bone is weak as the collagen fibres are irregular

+ Lamellar bone laid down
- collagen organised in regular sheets to give strength and resilience

Remodelling by osteoclasts to restore original bone shape

Question 20

What is the foetus cartilage model is replaced by?

Answer 20

Bone (ossification)

• endochondrial (long bones)
• intremembranous (flat bones)

Bone growth begins in the shaft during foetal life

Question 21

What is the foetus cartilage model is replaced by?

Answer 21

Bone (ossification)

• endochondrial (long bones)
• intremembranous (flat bones)

Bone growth begins in the shaft during foetal life

Question 22

Where is does ossification begin/primary ossification?

Answer 22

Diaphysis

Question 23

Where is does ossification begin/primary ossification?

Answer 23

Diaphysis

Question 24

Where is the secondary centre of ossification?

Answer 24

Epiphysis (epiphyseal plate)

Question 25

What are the zones of the epiphyseal plate?

Answer 25

\+ Ossification (osteogenic) zone
\+ Calcification zone
\+ Hypertrophic zone
\+ Growth (proliferating) zone
\+ Resting zone

Question 26

When does fusion of the epiphyseal plate occur?

Answer 26

By the end of puberty

Question 27

What is the chemical composition of bone matrix?

Answer 27

Calcium hydoxyapatite: (Ca5 (PO4)OH)

Question 28

What are features of the medullary cavity?

Answer 28

+ Contains bone marrow supported by cancellous bone

- red bone marrow is one site of haematopoiesis

Question 29

What are features of the resting zone?

Answer 29

On the epiphyseal side of the plate (reserve cells)

Question 30

What occurs at the growth zone?

Answer 30

Cells undergo mitosis (proliferation)

Question 31

What occurs at the maturation zone?

Answer 31

Cartilage cells are transforming and enlarging and the matrix calcifies

Question 32

What occurs at the osteogenic zone?

Answer 32

+ Calcified cartilage removed by osteoclasts

+ Replaced by bone secreted by osteoblasts