Bone

Question 1

-Osteology:
-Osteogenesis:
-Osteomyelitis:
-Osteopathy:
-Osteoporosis:
-Osteosarcoma:

Answer 1

-The study of bone
-The formation of bone
-An infection within the bone
-A disease of the bone
-Weak bone
-A cancer originating from bone-forming cells

Question 2

2 categories of the skeletal system and number of bones in them

Answer 2

Axial : 80 (skull, thoracic cage, vertebral column)
Appendicular: 126 (shoulder, upper limbs, pelvic, lower limbs)

Question 3

3 functions of bone

Answer 3

Mechanical
Synthetic
Metabolic

Question 4

Mechanical function of bone (3)

Answer 4

Protect important and delicate tissues and organs
Framework for shape and support
Form basis of levers for movement

Question 5

Synthetic bone function

Answer 5

Haemopoiesis (holds and protects red bone marrow)

Question 6

Metabolic function of bone

Answer 6

Mineral storage for calcium and phosphorous
Fat storage (yellow bone marrow)
Acid base homeostasis (absorbs or releases alkaline salt to help regulate blood pH)

Question 7

How does the bone help with acid base homeostasis

Answer 7

Absorbs or releases alkaline salts to help regulate blood pH

Question 8

2 types of bone

Answer 8

Cancellous
Compact (cortical)

Question 9

What is cancellous bone?

Answer 9

Spongy or trabecular bone - made up of plates called trabeculae with bone marrow in gaps
Cancellous bone forms a network of fine bony columns or plates called trabeculae to combine strength with lightness. The spaces are filled by bone marrow

Question 10

What is cortical/compact bone?

Answer 10

Dense outer layer of bone - 80% of body’s skeletal mass
Compact bone forms the external surfaces of ‘named bones’ and comprises ca. 80% of the body’s skeletal mass

Question 11

Describe the two ways bones are formed

Answer 11

Endochondral ossification: long bones from a CARTILAGE TEMPLATE - continue to lengthen by ossification of epiphyseal end plates

Intra-membranous ossification: bone from clusters of mesenchymal stem cells in the centre of the bone (interstitial growth) - forms cancellous bone

Question 12

What is the primary ossification centre in a foetus?

Answer 12

Where bone grows out from

Question 13

What are osteoblasts?

Answer 13

Bone forming cells - lay down osteoid which is converted to bone once mineralised

Question 14

What is the periosteum?

Answer 14

Membrane containing fibroblasts and mesenchymal stem cells (differentiate into osteoprogenerative cells) that surrounds the bone for bone deposition

Question 15

What are osteoclasts?

Answer 15

Multinucleated cells that secrete enzymes and acid to destroy bone

Question 16

What are osteocytes?

Answer 16

Bone cells found within the bone - can be broken down to give osteoblasts

Question 17

How is an osteocyte formed?

Answer 17

When an osteoblast becomes embedded in the matrix (osteoid) it has secreted and the matrix turns to bone

Question 18

In histology, how can you differentiate an osteoclast?

Answer 18

Always lying in a depression from reabsorbing/breaking down bone

Question 19

How is cancellous bone converted to cortical bone? (5)

Answer 19

1. MSC produce osteoblasts that bind to surface of cavity inside trabeculae
2. Osteoblasts lay down osteoid that turns to bone after mineralised - osteocytes are formed
3. Layer is then coated with osteoblasts again and the process repeats, creating lamellae (different layers in different directions) until small canal formed
4. Central MSC converted to blood vessels, lymph vessels, and nerves

Question 20

What is the central canal called within an osteon?

Answer 20

Haversion canal - food and information sent to osteocytes

Question 21

How are osteons connected?

Answer 21

Volkmanns canals - connects to haversion canal of other osteons

Question 22

What is an osteon?

Answer 22

Structural unit of compact bone consisting of lamellae - column structure going up length of cortical with a canal in the middle

Question 23

How do osteocytes communicate to eachother in an osteon?

Answer 23

Through cytoplasm projections

Question 24

Why can a bone resist fracture? How does it do this?

Answer 24

Great tensile and compressive strength -
Lamellae in osteon can slide across eachother to resist a fracture (no cells… water can resist compression)

Question 25

How is force distributed in bone?

Answer 25

Passed through cancellous bone to cortical, then distributed through cancellous bone at distal end so force is spread out

Question 26

Why does a bone remodel itself?

Answer 26

Fills in the weak spots of the cortical bone if the osteon is weak - haversion system is remodelled

Question 27

What is the key determinant of bone strength?

Answer 27

Exercise - increased osteon Inactivity increases bone reabsorption

Question 28

Describe in detail the process of bone re-modelling

Answer 28

1. Osteoclasts degrade bone and make tunnel called CUTTING CONE 2. As they do this, convert bone back to osteoid and release osteocytes- become osteoblasts 3. Osteoblasts fill in edges of cutting cone with osteoid, reshaping haversion system towards the weakness 4. Continues until original haversion canal is reached and cant build new bone on top of that 5. Osteoblasts make a smaller tunnel of cortical bone called the closing cone

Question 29

3 factors affecting bone stability

Answer 29

Activity of osteocytes (osteoid recycling) Activity of osteoblasts (bone deposition) Activity of osteoclasts (bone reabsorption)

Question 30

What is the activity of osteoblasts stimulated by?

Answer 30

Calcitonin, vitamin A, thyroid hormone, oestrogen, testosterone, GH

Question 31

What is the activity of osteoclasts stimulated and inhibited by?

Answer 31

Stimulated by parathyroid hormone - osteoclasts release calcium ions into blood Inhibited by calcitonin - block PTH receptors on osteoclasts

Question 32

How do osteocytes recycle osteoid?

Answer 32

Can act like osteoblasts and lay down scavenged osteoid into their lacunae (depression where they sit) Increased by oestrogen and thyroid hormone

Question 33

4 vitamins that can affect bone stability and why

Answer 33

Vitamin D3 - produces calcitriol for calcium absorption Vitamin C - synthesis of collagen which forms the matrix Vitamin K and B12 - synthesis of bone proteins

Question 34

Which vitamin is involved in the synthesis of collagen?

Answer 34

Vitamin C

Question 35

What characterises bone disease?

Answer 35

Depletion of bone mass

Question 36

What is brittle bone disease also known as?

Answer 36

Osteogenesis imperfecta

Question 37

Causes of osteogenesis imperfecta and the clinical consequences of this

Answer 37

Mutation in COL1A gene leading to incorrect production of collagen 1 fibres Weakened bones and increases fracture risk

Question 38

Why do sufferers of osteogenesis imperfecta often have shortened height and stature?

Answer 38

Bones are breaking constantly, but are unable to repair themselves properly

Question 39

What is rickets caused by?

Answer 39

Vitamin D deficiency Poor calcium mobilisation so collagen one cant be mineralised leading to weakened bone development

Question 40

Clinical features of rickets

Answer 40

Bowed legs - bones too soft so no strength to hold body Painful to walk Shortened height and stature

Question 41

What is osteomalacia?

Answer 41

rickets in adults Vitamin D deficiency

Question 42

What does osteomalacia cause? Why?

Answer 42

Softening of bones Lower mineralisation but osteoblasts are still making osteoid so weakened structure

Question 43

Who is affected mainly by osteomalacia?

Answer 43

Kidney disease - activates vitamin D Protected from sunlight - produced vitamin D e.g. XP, Muslim women Surgery - stomach and intestine where vitamin D absorbed Drugs - phenytoin prevents absorption

Question 44

What is osteoporosis?

Answer 44

Primary and secondary Loss of bone mass from holes in trabecular resulting in brittle and weak bones

Question 45

Describe the types of primary osteoporosis

Answer 45

Type 1: post menopausal women due to loss of oestrogen - stimulates osteoblast so osteoclast number increases and breaks down bone Type 2: older men and women - loss of osteoblast function (senile osteoporosis) due to low of both oestrogen and testosterone

Question 46

Describe secondary osteoporosis

Answer 46

Result of drug therapy e.g corticosteroids) Processes affecting bone remodelling e.g. malnutrition, immobilisation, weightlessness (space travel) Metabolic bone diseases

Question 47

3 modifiable risk factors for osteoporosis

Answer 47

1. Calcium intake 2. Exercises - needed to maintain bone mass 3. Cigarette smoking in women - effect oestrogen

Question 48

What is achondroplasia?

Answer 48

Form of dwarfism caused by mutation of FGF3 receptor gene An inherited mutation in the FGF3 receptor gene * FGF promotes collagen formation from cartilage (endochondral ossification affected; intra- membranous ossification unaffected) * Results in short stature, but normal-sized head and torso * Long bones cannot lengthen properly

Question 49

What type of ossification is affected by achondroplasia? What happens?

Answer 49

Endochondrial ossification affected - results in short stature but normal sized head as only the long bones cannot lengthen properly